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The use of appropriate epidemiologic methods in experimental design and data analysis is recognized as an important aspect of generating sound scientific evidence. This chapter discusses methodologies relevant to epidemiologic, outcome, and intervention studies, as they are applied to problems of healthcare-associated infections. We stress common pitfalls and focus particularly on limitations of the published literature in hospital epidemiology. Although many of the basic ideas of hospital epidemiology can be traced back to Semmelweis (1), the formal application of epidemiologic methods in infection control received a substantial boost during the 1970s and 1980s, with the publication of a number of methodologically oriented articles that brought innovation to the field (2, 3, 4, 5, 6, 7). These influential, seminal articles covered topics such as the relationship between prevalence and incidence, matched cohort study design, confounding, and effect modification. Based on the assumption that nosocomial infections have causal and preventive factors that can be identified through systematic investigation, these articles demonstrated convincingly that epidemiologic methods add important knowledge to reduce the rates of hospital-acquired infections. Thus, the conceptual framework was laid for many interventional and observational studies in the field. This chapter elaborates on this seminal body of work and brings to the readers' attention newer methodologies and principles. Recent advances in the conceptual underpinnings of epidemiology and selection of statistical models that facilitate causal inference may not have garnered widespread attention by infection control professionals and hospital epidemiologists. Using selected articles as examples, the quality of methods in the infection control literature is discussed and opportunities for improvement are highlighted. By necessity, our review of articles and choice of topics is selective. The criticisms and suggestions, which complement the information presented in Chapters 1, 2, 3, 4, are intended to be constructive. Some of our arguments may even challenge conventional wisdom, and in the process stimulate a fresh perspective on the literature in infection control and hospital epidemiology. The chapter is organized into five sections, based on specific recommendations for improving the quality of observational research in infection control and translating that research into action: Use terminology clearly and precisely. Search for and destroy confounding (as much as possible). Recognize selection bias in all of its guises. Account for timing of exposures and time at risk. Develop guidelines according to explicit rules. RECOMMENDATION 1: USE TERMINOLOGY CLEARLY AND PRECISELY Fundamental to scientific reasoning is the correct use of terminology. Several expressions used in hospital epidemiology are misnomers, well embedded in everyday use. Table 93.1 summarizes several commonly misused terms and suggests more accurate terms. TABLE 93.1. TERMINOLOGY: COMMONLY USED PROBLEMATIC AND AMBIGUOUS TERMS Commonly Used Name More Appropriate Term Explanation Prevalence rate Prevalence or prevalence proportion Prevalence is the proportion of a specified population with a condition or disease at a defined point in time. A rate is the magnitude of change of one entity divided by another entity. Rates have different units in the numerator and denominator. Prevalence rate is an example of a term in which the word rate is used inappropriately to mean proportion. Matched case-control study Matched cohort study Retrospective studies assessing the impact of nosocomial infections are comparing outcomes (deaths, costs) as the principal study measurement. Since the exposure is known (presence or absence of an infection) and the outcome unknown, it's a cohort study by definition. Mortality rate Case-fatality proportion or fraction Mortality rate is often used as a synonym for the incidence proportion of deaths in a study cohort due to the disease of interest. Similar to the term prevalence rate, it would be more accurate to use the terms case-fatality proportion or case-fatality fraction. Attributable fraction Excess fraction If the term attributable fraction is taken to mean the fraction of disease (or deaths) in which exposure was a contributory cause of disease, strong biologic assumptions are required. To avoid this problem, the term excess fraction is preferred. Confusion in Classification of Study Design and Use of Terms Case and Control Misnomers regarding terminology appear to be particularly common in conjunction with studies that examine outcomes of infections and other adverse events. If patients with a nosocomial infection are being compared to patients without nosocomial infection with respect to an outcome such as length of stay, mortality, or medical costs, a cohort study is being conducted, assuming that patients are selected on the basis of the presence or absence of infection. The infection constitutes the exposure. Similarly, studies in which outcomes of patients with a resistant microorganism are compared to outcomes of patients with the susceptible form of the microorganism are following a cohort design. If exposed and nonexposed subjects are matched on other criteria, such as age and severity of illness, the study is a matched cohort study. The distinction between matched cohort and P.1646 matched case-control studies is not just a semantic one. In a matched case-control study, it is necessary to perform a matched analysis if the matching factors are associated with exposure, even if they are not associated with the outcome, whereas in a matched cohort study this requirement does not exist (8). Abundant examples exist in which the terms case and control are used in the context of a matched cohort study, leading to confusion about the study design (9, 10). For instance, a recent study (10) about the “attributable mortality rate” of bacteremia due to methicillin-resistant Staphylococcus aureus (MRSA) claimed to perform a “retrospective cohort analysis and two independent case-control analyses.” As outlined above, this terminology is incorrect, since in all three analyses outcomes were compared and thus the term matched cohort studies would have been more appropriate. Multiple Meanings of the Term Attributable Perhaps nowhere is terminology in hospital epidemiology more confusing than in the use of the word attributable (11, 12, 13). This word is included in a myriad of epidemiologic terms with meanings that vary widely. The dictionary definition of attributable is “ascribed to” and, in epidemiology, it is frequently taken to be synonymous with “caused by.” However, there are two types of causation that often are not distinguished. During a defined follow-up period, an exposure may either shorten the interval to occurrence of disease or cause a disease case to occur that otherwise would not have occurred (14). The former is an accelerated disease case, whereas the latter is an excess case. If exposure prevents disease, this may be restated to indicate that exposure either lengthens the interval to occurrence of disease or averts a case from happening that otherwise would have occurred. The rationale for constructing formulas to measure the attributable fraction is that not all disease in exposed patients is necessarily due to exposure: some exposed individuals would have developed disease, even at the same time, if they had not been exposed. It is also evident that the ratio of exposed patients belonging to these two causal types, accelerated or excess cases, depends on the duration of the follow-up. It can be shown that, compared to the enumeration of excess cases, deriving an estimate of the number of accelerated cases relies on additional, more tenuous assumptions about the form of the causal relationship between exposure and disease. Hence, rather than attempting to estimate the fraction of exposed cases that are caused by exposure, it is generally preferred to restrict attention to excess cases. The occurrence of excess cases can be estimated by simply comparing the incidence proportion in exposed individuals to the incidence proportion in nonexposed individuals, assuming that confounding is absent. Due to these considerations, Greenland and Robins (15, 16) recommend use of the term excess fraction in place of attributable fraction when the objective is to quantify the fraction of exposed cases that are excess cases caused by exposure (15, 16). They reserve the term etiologic fraction to indicate the proportion of exposed cases caused by exposure, including both types of causation. The population excess fraction is an estimate of the fraction of all cases in the population that are excess cases due to exposure. The set of terms that cover these concepts are referred to as the family of attributable fractions (15, 17). RECOMMENDATION 2: SEARCH FOR AND DESTROY CONFOUNDING This section discusses the central challenge in epidemiology, namely, how to reduce confounding. Informative examples from the published literature that have relevance to key aspects of the problem of confounding have been selected for pedagogic purposes. Prior to evaluating the quality of the methods used in these investigations, we provide an in-depth explanation of why confounding is important and how it arises. There are four research questions covered by the articles, reworded here to be as explicit as possible: Does prolonged postoperative antimicrobial use increase the risk of nosocomial bloodstream infection compared to short postoperative antimicrobial prophylaxis? P.1647 How much does inadequate antimicrobial treatment of bloodstream infection in critically ill patients heighten the risk of death compared to adequate antimicrobial treatment? Among patients with bloodstream infections due to Staphylococcus aureus, does methicillin-resistance increase the risk of mortality compared to methicillin-susceptible infection? Does perioperative antimicrobial prophylaxis decrease the risk of wound infection after clean surgery compared to no prophylaxis? Background The surgeon who explains that the reason her patients have a higher infection rate is that she operates on sicker patients demonstrates an informal grasp of the concept of confounding. However, when it is necessary to conduct and analyze an epidemiologic investigation, this intuitive understanding of confounding reveals its limitations. We begin by offering two core principles that may run somewhat counter to conventional wisdom: It is not possible to use statistical criteria alone to recognize confounding, or determine whether it has been removed. Confounding is identifiable only in the context of a causal model (18, 19, 20). Confounding is present when there is discordance between the true causal effect of an exposure on disease or other outcome in a target population and the measured association between exposure and disease (21). Thus, an exploration of confounding starts with an exposition on causation. What is meant by true causal effect? Causation is best understood in terms of the question, What would have happened if the exposure had not occurred? Stated another way, the causal effect of exposure in exposed individuals is represented by the difference between their actual disease status and what would have happened if everything else had been the same up until the time of exposure, but that they had then not been exposed or exposed to a different degree (21). Under this formulation, causation is defined on the basis of a comparison between outcomes under mutually exclusive conditions, exposed and unexposed or, alternatively, varied levels of exposure. However, in any single patient, only one of these conditions is observed. In the absence of time machines to replay experience under dissimilar exposure conditions, a straightforward way to directly measure causal effects is not available. When exposure is randomly allocated, it is possible to derive an estimate of the unconfounded, average causal effect of exposure, with a random error correlated with sample size. In the absence of random allocation of exposure, causal inference relies on untestable beliefs regarding causal relationships and unmeasured confounders (22). It is useful to depict assumptions about causal relationships in a graphical format to identify potential sources of confounding. The causal effects of exposure on disease may be visualized as arrows aiming from exposure to disease (Fig. 93.1). These arrows represent the postulated causal mechanisms or pathways by which exposure affects the outcome or disease. Causal pathways that link exposure (E) and disease (D) may be direct or indirect. An indirect pathway is characterized by the presence of an “intermediate variable” (I) that mediates a causal effect, whereas a direct effect lacks an intermediate variable (23). The causal null hypothesis is the assumption that there are no indirect or direct causal pathways pointing from exposure to disease. Graphical representations of causal relationships are called directed acyclic graphs (DAGs) (18, 24, 25, 26). Figure 93.1. Graphical representation of causal relationships illustrated by directed acyclic graphs (DAGs). An exposure (E) has both direct and indirect effects on disease (D). The indirect effects are mediated by an intermediate variable (I). A confounding factor (C) is a cause of both the exposure (E) and the disease (D). Confounding arises when direct or indirect causes of exposure are also direct or indirect causes of disease status. When exposure is a type of treatment and confounding is due to factors that influence treatment selection, the term confounding by indication is sometimes used (27). Causes of exposure can be visualized as arrows pointing toward exposure. If these inputs into exposure also have outputs connecting to disease through paths that do not include exposure, noncausal pathways from exposure to disease exist. The labeling of a pathway as noncausal is done from the perspective of exposure and disease. If research questions pertain to multiple exposures, the postulated connections between each factor of interest and disease may, in turn, be divided into causal or noncausal pathways. Noncausal pathways create an association between exposure and disease, one that is not a consequence of exposure, hence the need to block the noncausal pathways if the goal is to estimate the true causal effects of exposure. Factors located within these noncausal pathways are usually associated both with exposure and disease, although in any given study these associations may themselves be obscured by confounding, and therefore not manifested (21, 28). Successful randomization eliminates confounding by breaking the causal inputs into exposure or treatment. It makes the exposure or treatment actually received independent of what would have happened had exposure been absent or altered. This principle, which is surprisingly difficult to grasp, is another way to define the absence of confounding. The goal of epidemiology is to attempt to accomplish this feat with respect to measured confounders, using appropriate design and analytic strategies (28). Perhaps what poses the most difficulty to individuals conducting epidemiologic research and readers of the literature is the myriad of statistical techniques available to analyze data. These statistical methods are not reviewed in detail here. Detailed recommendations for conducting methodologically sound multivariable analyses of observational studies have been summarized elsewhere (29, 30, 31). Rather, our goal is to emphasize the P.1648 distinction between the statistical evaluation of association and the identification of confounding. Contrary to widespread belief, the p-value is not a useful test of confounding. Even the comparison of crude and adjusted measures of association is an inadequate approach by itself to detect confounding. Depending on the causal model, the adjusted measure of association may be more or less confounded than the crude measure. The judgment of whether an adjusted association is less confounded than a crude association relies on assumptions about the causal relationships between exposure, outcome, and the adjustment variables (25). Example 1: Prolonged Antimicrobial Prophylaxis The first step toward reducing confounding in observational research on causal effects is to recognize its potential existence and to obtain measurements on potential confounders or to account for potential confounding during the design phase of the study. Sometimes these initial steps are omitted, as the following example illustrates. Many investigators have examined the effect of antimicrobials on subsequent occurrence of infection. Under certain conditions, systemic antibiotic use may decrease the risk of nosocomial infection. For instance, this has been demonstrated in clinical trials of nosocomial pneumonia in ventilated patients (32, 33, 34). An opposite effect of antimicrobial prophylaxis was suggested in a study that found that duration of antimicrobial prophylaxis after major surgery was associated with a significantly increased risk of nosocomial bloodstream infection (BSI) (35). The authors of this study observed six cases of BSI among 180 patients receiving short antibiotic prophylaxis, compared with 16 cases of BSI in 94 patients with extended antibiotic prophylaxis [crude odds ratio (OR), 5.9]. These results were presented without any consideration of the possibility of confounding. In an observational study we conducted of the relationship between duration of antimicrobial prophylaxis and infections (36), we also found a strong association between prolonged antibiotic prophylaxis and subsequent nosocomial BSI in the crude analysis. A total of 2,641 patients undergoing cardiac surgery were included in the study, divided into those in whom antimicrobial prophylaxis was short (<48 hours) and those in whom antibiotic prophylaxis was prolonged (>48 hours) (36). The unadjusted analysis revealed an odds ratio of 3.3, based on the occurrence of 27 cases of nosocomial BSI (1.8%) after 1,478 procedures using short antibiotic prophylaxis compared with 65 cases of nosocomial BSI (5.7%) after 1,139 operations with prolonged antibiotic prophylaxis. The problem with this crude analysis was that length of follow-up and intensive care unit (ICU) stay affected the likelihood of receiving prolonged antimicrobial prophylaxis. Using survival analysis methods removed confounding related to differences in length of follow-up; the apparent association appeared smaller [hazard ratio (HR), 1.7] based on Cox proportional hazards regression. Seventy-seven percent of cases of nosocomial BSI occurred in patients who stayed more than 4 days in the ICU. Similarly, extended antibiotic prophylaxis was correlated with longer ICU stay. After stratifying for length of ICU stay, prolonged antibiotic prophylaxis was not associated with a significantly increased risk of BSI (HR, 1.4). In an additional analysis, we showed that prolonged antibiotic prophylaxis did not decrease the incidence of surgical site infection; however, it increased the risk of isolation of resistant gram-negative bacteria and vancomycin-resistant enterococci (37). In summary, these results demonstrate confounding of the crude association between prolonged antibiotic prophylaxis and nosocomial BSI by differences in follow-up and length of ICU stay (36). Example 2: Inadequate Antimicrobial Therapy More often, investigators do attempt to address confounding, but use analytic methods that are suboptimal. A common error is to identify confounders primarily on the basis of the statistical significance of the association between the outcome and potential confounders. This tactic is inappropriate when the purpose of the regression model is to estimate the magnitude of the causal effect of an exposure on an outcome. As an example, consider studies that have examined the impact of inadequate antimicrobial treatment of infection on patient outcomes (38, 39, 40, 41, 42, 43). This is a research question that is not amenable to direct testing in a randomized trial, since it would be unethical to willingly expose patients to inappropriate treatment. To answer the question, therefore, we have to rely on observational studies. On the face of it, it is highly likely that inadequate antimicrobial therapy does have some negative effect on outcome in critically ill patients. The key objective of an observational study, then, is to remove as much of the confounding as possible so as to obtain an unbiased estimate of the magnitude of effect of inadequate therapy. In one such widely cited study of patients in the ICU with BSI, therapy was defined as inadequate if the antimicrobials being given to the patient were ineffective against the causative pathogen at the time that identification and susceptibility results were reported by the clinical microbiologic laboratory (44). The crude relative risk for mortality after inadequate therapy compared to adequate therapy equaled 2.2, corresponding to a crude odds ratio of 4.1 (44). The “adjusted” effect estimate of inadequate antimicrobial treatment of BSI on hospital mortality had an odds ratio of 6.9, after including use of vasopressors, age, organ dysfunctions, and severity of illness, along with inadequate therapy, in a multivariable logistic regression model. A major limitation with this analysis was that the factors included in the logistic regression model were only those found to be significantly associated with mortality. A stepwise variable selection approach was used, with a p-value of .05 as the limit for the acceptance or removal of new terms. The problem is that this method does not remove confounding by factors not selected into the model. Many characteristics were identified that distinguished patients with inappropriate and appropriate antimicrobial use, such as time in the hospital prior to BSI, prior use of antimicrobials, and serum albumin. Presumably, these were factors that directly or indirectly influenced the probability that treatment was inadequate or were proxies for such factors. Some of these factors were also associated with the outcome, but not always to a statistically significant degree. Not including P.1649 these factors in the model likely contributed to an exaggerated estimate of effect (44). All observational research is limited by the possibility of residual confounding due to unmeasured variables, but given a postulated causal model and a set of measured variables, some analytic strategies are less prone to confounding than others (25, 45). The key point is that confounders do not have to be statistically significantly associated with the outcome to be confounders. As stated in the background section, the results of statistical hypothesis testing are tangential to the recognition of confounding. To some extent, the notion that confounders should be significantly associated with the outcome reflects the belief that the only “true” associations are ones that are statistically significant. Instead of focusing on statistical significance, the analysis should be directed toward a careful consideration of the potential sources of confounding and deriving the least biased estimate of the true causal effect. A frequently overlooked problem with conventional regression models is that they impose assumptions regarding the form of the relationship between the additional model factors and the outcome, and between these additional factors and the exposure, which, if incorrect, may increase confounding (31). The association parameter derived from the regression model provides an estimate of the unconfounded causal effect of exposure only when all of the assumptions of the multivariable model are correct. In addition, automated variable selection methods completely ignore the relationship between the putative confounders and the exposure. If the factors selected into the model are affected by exposure, their inclusion may also be deleterious with respect to confounding. This problem is discussed in more detail below. Traditional stratification methods have an advantage over regression models because they involve fewer assumptions, but they lead to sparse numbers within strata when multiple confounders are present (46). Newer analytic strategies have been developed that overcome some of these types of problems and allow improved causal inference. These more robust methods start with specification of the exposure of interest and build on an explicit structural model of causal relationships (45, 47). Another recent advance in epidemiology is the use of simulation to increase the flexibility of sensitivity analyses of confounding and other types of bias (48, 49). One analytic method that has gained widespread application is the use of propensity scores, particularly for point exposures that are dichotomous or categorical (50). The propensity score is the probability of exposure or treatment based on factors that influence treatment, and thus lies between 0 and 1 (51, 52). A multivariable logistic regression model is typically used to estimate this probability and, most commonly, the propensity score is used as either a matching or stratification variable to remove confounding by indication due to measured factors (53). The propensity score method relies on assumptions about the form of the relationship between the confounder and exposure but is less susceptible than traditional models to bias by misspecification of the relationship between the confounders and the outcome (54). Example 3: Excess Mortality Due to MRSA Bloodstream Infection Including a variable for adjustment sometimes increases confounding rather than reduces it. This happens when the adjuster is a consequence of the exposure of the interest, and either lies on one of the causal paths between exposure and the outcome or also is an effect of the outcome (26). A number of investigators have compared outcomes in patients with resistant and susceptible infection (10, 55, 56). In such studies, it is especially crucial to precisely specify the causal hypothesis of interest. Often, it pertains to the virulence of the microorganism: Do infections due to the resistant form of the microorganism have worse, similar, or better outcomes than infections due to the susceptible form of the microorganism? One such study measured mortality following BSI, comparing infections due to MRSA and to methicillin-susceptible S. aureus (57). One of the control variables included in the logistic regression model was the presence of shock, presumably measured at the time of detection of BSI. The problem is that one path by which methicillin-resistance may raise the mortality rate is by increasing the risk of shock. Controlling for shock produces bias in the estimate of effect of methicillin-resistance toward the null by blocking one of the causal pathways linking the exposure and outcome. More suitable adjusters would be measures of severity of illness, such as APACHE score, taken prior to onset of symptoms and signs of infection. On the other hand, if the study goals were to address the question whether inadequate therapy of methicillin resistance caused an increase in mortality compared to adequate therapy of methicillin-resistant or methicillin-susceptible infection, shock at the time of detection of infection, prior to initiation of therapy, would be an appropriate adjuster. In this situation, shock is no longer causally downstream of the exposure of interest. Example 4: Antimicrobial Prophylaxis in Clean Surgery The final example is of a publication in which confounding was addressed in an appropriate fashion (58). The purpose of the study was to evaluate the effect of antimicrobial prophylaxis on surgical site infection after clean surgery. Control variables included in the analysis were factors that possibly influenced both the decision to prescribe antibiotic prophylaxis and the outcome of interest (surgical site infection in clean surgery). The observational study, of patients undergoing herniorrhaphy or selected breast surgery procedures, was done in conjunction with a randomized clinical trial of perioperative prophylaxis (59). Patients were included in the observational cohort if they did not participate in the clinical trial. Thirty-four percent of patients (1,077/3,202) received prophylaxis at the discretion of the surgeon; 86 surgical site infections (2.7%) were identified. The unadjusted odds ratio for infection comparing prophylaxis recipients with nonrecipients was 0.85 (26/1,077 vs. 60/2,125). The odds ratio after adjustment for duration of surgery and type of procedure was substantially lower, at 0.59, indicating a 41% reduction in the odds of surgical site infection following prophylaxis. Additional adjustment for age, body mass index, the presence P.1650 of drains, diabetes, and exposure to corticosteroids did not change the magnitude of this effect meaningfully. The conclusion of the investigators was that the clinical criteria individual surgeons were using to decide which patients should receive prophylaxis were successfully targeting patients within the clean surgery group who were at higher risk for infection. Thus, this study confirmed results from the randomized study (59), and showed that after correct adjustment for confounders, prophylactic antibiotics were beneficial in the nonrandomized patients. RECOMMENDATION 3: RECOGNIZE SELECTION BIAS IN ALL OF ITS GUISES Selection bias occurs when the selection of study subjects induces a noncausal association between exposure and disease. Thus, the end result is similar to confounding: it leads to distortion of the measured association between exposure and disease away from the true causal effect (60, 61). For a variety of reasons, selection bias tends to be more common in case-control studies than cohort studies, although this need not be the case if the case-control study is rigorously conducted (60, 61). In the case-control study, subjects are chosen for inclusion according to case status (e.g., presence or absence of a resistant microorganism). The key principle is that controls should be an unbiased sample of the source population with respect to exposure (60, 61). Just as in a cohort study, it is necessary to delineate the source population or study base—individuals who would be classified as cases if they developed the disease, or alternatively, the person-time experience during which there is eligibility to become a case. The failure to select subjects independently of exposure status distorts the causal relationship between exposure and disease. If subject selection is influenced by a factor that is associated with exposure, the consequence is selection bias. The result is that distribution of exposure in controls will differ in a systematic way from that of the entire study base. The sampled exposed and unexposed individuals will no longer be comparable with respect to disease incidence; a noncausal exposure-disease association is induced. Antimicrobial Use and Risk of Infection with Resistant Microorganisms Case-control studies on antibiotic-resistant microorganisms typically aim to determine risk factors (e.g., specific antimicrobial agents) causally related to colonization or infection with resistant pathogens (62, 63, 64, 65, 66, 67, 68). The choice of appropriate controls is central to the validity of results in those studies (69, 70). We will look at studies of antimicrobial risk factors for infection with vancomycin-resistant enterococci (VRE), which have been plagued by suboptimal selection of controls (69). If the exposure of interest in a case-control study of VRE acquisition is vancomycin use, then controls should be selected that are representative of vancomycin exposure in the entire cohort of hospitalized patients. Controls should not be intentionally limited to certain wards where vancomycin use is low since this would falsely overestimate the odds ratio obtained for vancomycin. Often, for convenience reasons, patients with vancomycin-susceptible enterococci (VSE) are selected as the control group. The reason the choice of patients with susceptible microorganisms as the control group leads to a biased estimate of relative risk is that a distorted estimate of exposure frequency in the source population is obtained. The selection bias introduced by using control patients with susceptible microorganisms is likely to have the strongest impact on estimating the effect of exposure to antibiotics that are active against susceptible (but not resistant) microorganisms, which is often the exposure of greatest interest. The reason for this particular bias is that treatment with active antibiotics likely inhibits the growth of susceptible microorganisms, therefore making this exposure less frequent among patients who are culture positive for susceptible microorganisms than among patients in the source population. Thus, vancomycin therapy may be identified as an individual risk factor not because it is a risk factor for development of VRE but because fewer patients in the VSE comparison group received vancomycin. Vancomycin may be causal only with respect to its killing effect on VSE, not to its effect to enhance risk of VRE acquisition (71). The selection bias associated with this type of control group selection was demonstrated in a meta-analysis that aimed to assess whether vancomycin therapy was a risk factor for development of VRE (72). Studies that used a control group of patients with VSE identified vancomycin therapy as a risk factor (pooled OR, 10.7), whereas studies that used a second control group (no patients with VRE and not limited to patients with VSE, therefore similar to the base population of hospital admissions) revealed a far weaker association (OR 2.7). This weaker association was then eliminated when the analysis was limited to studies that also controlled for time at risk prior to the outcome (72). Another situation in which selection bias may be a problem results from the use of clinical cultures to identify patients with a resistant microorganism. If the exposure influences performance of the test used to identify the resistant microorganism or is itself influenced by a factor that affects culturing, the consequence is selection bias. This is similar to the well-described selection bias that occurred when investigators attempted to study the effect of estrogen replacement therapy on uterine cancer (18). The disease and the exposure both affected vaginal bleeding, a symptom that influenced the likelihood of detection of uterine cancer. In the example of studies of resistant microorganisms, when the exposure of interest is antimicrobial use, factors that may influence both future culturing practices and prescribing of antimicrobials are the initial symptoms and signs of infection. Adjusting for the clinical manifestations of infection and other indications for antimicrobial use can remove this selection bias. RECOMMENDATION 4: ACCOUNT FOR TIMING OF EXPOSURE AND TIME AT RISK Time at Risk There are two common ways that time is misunderstood or mishandled in epidemiologic studies within the field of infection control. One pertains to the concept of time at risk and the other to time-varying exposures. The key role of time in the occurrence and detection of disease is worth emphasizing. First, time at risk P.1651 serves as the stage on which other causes act. For instance, the longer the patient is hospitalized, the greater the opportunity for the patient to experience the use of invasive medical devices that are causes of nosocomial infection and the higher the cumulative probability of occurrence of a nosocomial infection. Second, even for those causes that are experienced at a single point of time, for instance, ingestion of food contaminated by Listeria (73), time is important because of the induction period. If the follow-up time is shorter than the maximum interval from exposure to onset of symptoms (incubation period), the case may not be detected. Third, time at risk itself may act as an intermediate variable, mediating the effects of other causes of disease. One of the indirect pathways by which high illness severity leads to higher infection risk is by increasing the length of hospital stay. Fourth, exposures may not be constant during the period of risk; accounting for time-varying exposures poses additional problems discussed in more detail below. Consider what actually constitutes the time at risk for nosocomial infections, using the situation in which only the initial infection is studied. An individual's time at risk for a nosocomial BSI begins when he or she is admitted to the hospital and ends at the time of occurrence of the first BSI or at discharge. More precisely, information about the presumed incubation period may be used to modify the start and stop times of this interval. The first 48 hours after hospitalization is “immortal time” in the sense that, by the usual case definition, events with onset during that interval are excluded. Conversely, infections detected up to a certain number of days after discharge may be included as cases, and so the follow-up time may extend for a brief period postdischarge (74). Notwithstanding these subtleties, the time at risk is approximately the hospital length of stay for individuals who do not experience a BSI and the interval from admission to occurrence of the infection for those that do. When the time at risk varies substantially from individual to individual, the incidence rate, denominated by person-time experience, is the appropriate measure of disease frequency. This concept is widely understood in infection control and forms the basis for measures of disease frequency such as number of catheter-related infections per 1,000 catheter days (75, 76). However, the implication of variation in time at risk for the choice of the target measure of effect is less often recognized. Generally, if there is a need for adjustment on time-at-risk, the target parameter of an epidemiologic analysis should be person-time based, usually the incidence rate ratio or hazard ratio (HR) (77, 78). Analyses of data from case-control or cohort studies using logistic regression often neglect this issue (79, 80, 81). Sometimes in such analyses, the time at risk is treated as a conventional risk factor (82, 83). Although this approach may be less biased than not accounting for time at risk at all, it neglects the distinction between time at risk and other types of confounders (84). A related limitation is to use hospital length of stay for all patients, regardless of case status, as the adjustment variable (85). A comparable type of inaccuracy is to calculate incidence densities using total person-time instead of person-time at risk (86). Time-Varying Exposures and Matched Cohort Studies The analytic techniques that account for variation in time at risk are particularly valuable when exposures change over time (87). An exposure is considered time varying when its value changes in a meaningful way during follow-up. In outcome studies of nosocomial infections or other adverse events, in which the aim is to estimate the causal effect of infection on endpoints such as mortality or costs, the infection is a time-varying exposure. Infected patients are deemed exposed after onset of the infection. Prior to infection, patients are unexposed, as are patients who never experience infection. The interval from start of follow-up to onset of infection differs from patient to patient. The most commonly used method to estimate excess morbidity and mortality caused by nosocomial infection or other adverse event is to perform a matched cohort study, in which patients with the adverse event are matched to one or more reference patients who did not experience the adverse event (88, 89, 90, 91). Infected and uninfected patients are usually matched for age, the underlying disease, as well as additional variables that may have contributed to excess morbidity and extra length of hospital stay (Fig. 93.2). Figure 93.2. A schematic design of a matched cohort study. Arrows indicate exposure to risk factors for infection after admission. Patient A is considered as uninfected reference patient (“RE”) for “case” patient B (“CA”) who developed nosocomial infection indicated by the broken arrow. This study design has several limitations because of the time-varying nature of the exposure. One source of bias occurs when infected and uninfected patients are compared with regard to total hospital costs or total hospital length of stay (88, 91, 92). For infected patients, only those costs incurred after the occurrence of the nosocomial infection are possibly secondary to infection. Prior to occurrence of infection, patients are unexposed. The association between preinfection outcome and infection is entirely noncausal from the perspective of measuring the excess burden of infection. Therefore, combining preinfection outcomes with postinfection outcomes dramatically amplifies confounding. Modifying the analysis such that average postinfection length of stay in infected patients is compared with average total length of stay in noninfected patients does not completely remove confounding by time (93). Bias persists even in matched cohort studies in which noninfected patients are selected to have a hospital length of stay at least as long as the interval to infection P.1652 in the corresponding infected patient, irrespective of differences in severity of illness. The reason for this bias is that conditioning on presence or absence of infection induces an association between the time to infection and time to discharge. Several recent studies have demonstrated the effect of this bias. Outcome analyses that did not account for the time prior to the occurrence of the infection or adverse event yielded different results than studies that did account for the time prior to the infection. As shown in Table 93.2, there is an important difference in excess length of stay between conventional matching approaches and methods that adequately model the timing of events (94). Schulgen et al. (95) tested different methods and showed that the use of unmatched or matched comparisons between noninfected and infected patients led to an overestimation of the excess length of stay due to surgical site infections or nosocomial pneumonia, compared to analyses based on a structural formulation of transitions between different states (Table 93.2). Similarly, Asensio and Torres (96) found that regression models yielded lower estimates of the excess length of stay and cost due to nosocomial infection than a matched-pair comparison. TABLE 93.2. ESTIMATED DURATION OF EXTRA STAY IN DAYS PER INFECTED PATIENT AND 95% CONFIDENCE INTERVAL (CI) FOR TWO STUDIES ON THE EFFECT OF SURGICAL SITE INFECTION (STUDY I) AND ON NOSOCOMIAL PNEUMONIA (STUDY II) Surgical Site Infection (Study I) Nosocomial Pneumonia (Study II) Approach Estimated Extra Hospital Stay 95% CI Estimated Extra Stay in ICU 95% CI Two-group comparison 20.7 18.4-23.0 14.4 10.7-18.2 Confounder matching 16.9a 12.9-20.9 12.3 9.7-14.9 Confounder and time matching 11.4b 7.1-15.7 8.2 5.9-10.5 Method 1 9.8 5.7-13.8 3.4 0.8-6.0 Method 2 11.5 8.9-14.0 4.0 1.5-6.1 a Matching for age, sex, diagnosis, and degree of contamination of wound. bMatching for age, sex, diagnosis, degree of contamination of wound, and time to infection. Study I used a Markov transition state model and study II used a structural nested failure time model. Both studies account for the time from admission to nosocomial infection in the estimation of the effect of nosocomial infection on subsequent length of stay. Adapted from Schulgen G, Kropec A, Kappstein I, et el. Estimation of extra hospital stay attributable to nosocomial infections: heterogeneity and timing of events. J Clin Epidemiol 2000;53(4):409-417. Another approach to estimating cost and length of stay effects of adverse events is to apply survival models, in which the adverse event is incorporated as a time-dependent variable (97). This strategy can be applied to costs as well as length of stay (97). Even when the time-varying nature of the exposure is accounted for, it is still necessary to adequately adjust for traditional confounders, those factors that both increase risk of infection and affect the outcome of interest (98). For instance, Soufir et al. (13) investigated the excess risk of death due to catheter-related bloodstream infection (CR-BSI) in a cohort of critically ill patients. The crude case-fatality ratio was 50% and 21% in patients with and without CR-BSI. The statistical method of adjustment was based on Cox proportional hazards regression, with inclusion of matching variables and prognostic factors for mortality. CR-BSI remained associated with mortality following adjustment for prognostic factors at ICU admission (HR, 2.0; p = .03). However, after controlling for severity scores calculated 1 week before CR-BSI, the increased mortality was no longer significant in the Cox model (HR, 1.4; p = .27). In summary, nosocomial infections unquestionably have substantial effects on morbidity and mortality. However, the matched cohort study design produces bias in the estimation of the effects of nosocomial infection on length of stay and costs. Cost effects or excess length of stay are likely to be overestimated if the interval to onset of nosocomial infection is not properly accounted for in the study design or analysis (95, 99). Finally, appropriate statistical methods are important in analysis of excess costs associated with nosocomial infections, because informed decisions and policy developments may depend on them (98). Additionally, exaggeration of excess costs may lead to unintentional errors in the economic analysis of intervention programs. RECOMMENDATION 5: DEVELOP GUIDELINES ACCORDING TO EXPLICIT RULES Translating research in infection control into practice guidelines involves as the first step a rigorous review of evidence. Although expert opinion is a critical component of the development of recommendations and guidelines, it is important, whenever possible, to use results of the highest quality studies possible as the basis for infection control policy (100). This is crucial, because many practices in infection control have not been validated by controlled clinical trials. For instance, due to the lack of randomized studies, misconceptions about the value of alcohol-based hand disinfection widely persisted during the 20th century in most English-speaking countries (101). Alcohol-based hand gels have now been introduced in the United States and other English-speaking countries, although no controlled clinical trial has been published to determine whether alcohol-based hand gels are as effective as alcohol-based hand rinses. Only in vitro experiments have been conducted, and these have generated substantial controversies (102, 103). There are numerous other examples about scientific uncertainty in infection control. Unfortunately, there are many important questions in infection control for which we may never obtain data from randomized trials because of limitations in funding, lack of feasibility, and ethical dilemmas (104). P.1653 Methodologic Quality of Guidelines in Infection Control Guidelines are widely used and cited, because they attempt to summarize and critically appraise currently available evidence and give recommendations for daily practice (105). By contrast, individual trials are often conflicting or nondefinitive, because of their small sample size or other methodologic limitations. Many guidelines rely on reviews that were either previously published or created by guideline developers. Systematic reviews can aid in guideline development, because they involve selecting, critically appraising, and summarizing the results of primary research. The more rigorous the review method used and the higher the quality of the primary research that is synthesized, the more evidence-based the practice guideline is likely to be (106). Conversely, the quality of a review is compromised if a comprehensive search is not made to ensure that all potentially relevant articles are considered for inclusion, if the selection of studies is not reproducible or is open to bias, if the methodologic quality of the primary studies is not evaluated, or if possible reasons for the variability in results are not explored (107). Table 93.3 summarizes the most commonly used levels of evidence of preventive or therapeutic interventions, and the grading scale for recommendations made in practice guidelines. TABLE 93.3. LEVELS OF EVIDENCE AND GRADES OF RECOMMENDATIONS FOR PREVENTIVE OR THERAPEUTICAL INTERVENTIONS Quality of evidence I Evidence obtained from at least one properly randomized clinical trial with high power II-1 Evidence obtained from clinical trials with low power or without randomization II-2 Evidence obtained from well-designed cohort or case control studies II-3 Evidence obtained from studies using historical cohort comparisons III Descriptive case series without controls or opinions of respected authorities Strength of recommendation A Good evidence to support a recommendation B Fair evidence to support a recommendation C Insufficient evidence to recommend for or against a recommendation D Fair evidence to withhold a recommendation E Good evidence to withhold a recommendation Adapted from the rating scale used by the U.S. Preventive Services Task Force. Many guidelines in the infection control literature are not following the highest possible methodologic standards for development of guidelines, as suggested by the Cochran review group (108). For instance, the new guideline on preventing catheter-related infections published in 2002 named about eight different groups involved in the task force, but did not outline how the data were assembled or judged (109). The recently published hand hygiene guideline (110), an otherwise exemplary appraisal of the evidence, also did not include a detailed description of the systematic review process. Finally, the new Society for Hospital Epidemiology of America (SHEA) guideline for preventing nosocomial transmission of multiresistant Staphylococcus and Enterococcus may have upgraded the level of evidence generated by studies arguing in favor of screening cultures (111). Thus, these guidelines leave uncertain the study selection criteria, data extraction process, and quality of the included studies. To improve the quality of evidence, investigators assembling consensus guidelines should add more systematic information about the search methods, data sources, study selection criteria, and details about study designs, interventions, settings, and the quality of studies included in their recommendations. These recommendations have been followed in several practice guidelines published recently (112, 113). CONCLUSION We have critically assessed selected articles from the hospital epidemiology and infection control literature to highlight methodologic limitations and areas in need of improvement. We hope that this review will act as a stimulus to further research, based on sound methodologic tools, and that the resulting body of work will advance new hypotheses for the prevention of nosocomial infections. Assuming that healthcare-associated infections have causal and preventive factors that can be identified through systematic investigation of different populations, epidemiology has the potential to contribute substantially to the understanding of the effectiveness of infection control measures and act as a driver of practice change. As in any scientific endeavor, the fundamental challenge in hospital epidemiology is to ask the important questions and then select the right methods to answer them. The availability of systematic epidemiologic methods for use in infection control provides an opportunity for more complete prevention of nosocomial infections in the next millennium. ACKNOWLEDGMENTS We thank Michael Rubin and Marc Lipsitch for helpful comments and Didier Pittet for providing Figure 93.2. REFERENCES 1. Harbarth S. Epidemiologic methods for the prevention of nosocomial infections. Int J Hyg Environ Health 2000;203(2):153–157. 2. Haley RW, Schaberg DR, Von Allmen SD, et al. 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Since the second edition of this book was published in 1999, access to healthcare literature has continued to become easier, faster, and more widespread. The Internet features prominently as a primary repository for healthcare information. Indeed, many of the traditional forms of literature such as journal articles and books are available in their entirety on the Internet. More quality-filtered and patient-ready resources are available to help streamline the search for information. Finally, a new form of technology has invaded the information scene: the handheld or personal digital assistant (PDA). In this updated chapter, we explore the improvements in information access to evidence-based resources with relevance to infection control. We review these new resources and improvements in old ones as they relate to three areas in which a healthcare professional would require high-quality information: (a) solving clinical problems, (b) keeping up-to-date, and (c) setting clinical policy. USING THE LITERATURE TO SOLVE CLINICAL PROBLEMS Quick and efficient access to high-quality reliable information is never so important as when faced with a pressing clinical problem. This is especially true in the rapidly changing field of infection control in which practices and policies are subject to frequent changes and amendments. To make informed clinical decisions, recent reports are needed of systematic reviews or major preplanned human investigations relevant to the clinical setting. One could rely on one's colleague down the hall—if one has a colleague and he or she is more up to date and has time when one needs them†or one can search the literature to find the current best evidence by carefully defining the clinical question, choosing the most appropriate information source, and designing a search strategy (1). Until recently, textbooks were often sources for basic information that did not change quickly (2). Anatomy plus physiology and other such basic science subjects lend themselves well to the publication pace of textbooks. With the publication potential of the Internet, however, clinical practice textbooks have entered an “evidence-based era.” Many textbooks are now available on the Internet and integrate evidence-based information with specific clinical problems. In addition, they are updated more or less regularly. Up-To-Date (http://www.uptodate.com) is an evidence-based electronic textbook [Web-based and compact disc read-only memory (CD-ROM)] for general internal medicine and a growing number of other specialties. WebMD Scientific American Medicine http://www.samed.com) is also available on the Internet and CD-ROM. Clinical Evidence, from the BMJ Publishing Group, is a dynamic electronic synthesis of evidence from randomized trials, published in print, on CD-ROM, and on the Internet in unabridged, concise, and PDA formats. Organized by clinical area, the focus of each section is a selection of clinical questions and answers most often related to therapies. New and updated topics are posted online each month. The questions in Clinical Evidence concern the benefits and harms of preventative and therapeutic interventions, with emphasis on outcomes that matter to patients. The Physicians' Information and Education Resource (PIER) is a new Web-based service from the American College of Physicians-American Society of Internal Medicine (ACP-ASIM) (http://www.pier.acponline.org). Volunteer physician editorial consultants review the literature and prepare PIER modules for specific topics. The consultants are given recent citations to relevant articles obtained through filtered electronic searches. The modules are updated quarterly and made available on the Internet. Coverage includes diseases, screening and prevention, complementary and alternative medicine, ethical and legal issues, and procedures. The design of Clinical Evidence and PIER also make them useful for keeping up with the medical literature and for providing basic knowledge on healthcare topics. The Cochrane Library contains the collected work of the Cochrane Collaboration, an international organization that prepares, maintains, and disseminates systematic reviews of controlled trials of healthcare interventions (note that topics such as P.1640 diagnosis and prognosis are not covered). Within the Cochrane Library, the Cochrane Database of Systematic Reviews (CDSR) contains reviews that have high standards for finding, rating, summarizing, and reporting the evidence from trials (1). The Cochrane Library is searchable, contains almost exclusively controlled trials and systematic reviews, and is much smaller than MEDLINE, so that methodologic filtering is not needed and a simple, even one-word, search strategy will likely retrieve high-quality evidence with a clinical bottom line. Furthermore, the Cochrane Library is cumulative, and the reviews are regularly updated or tagged as no longer current, if not updated within a specified period. The Cochrane Library also contains summaries of non-Cochrane systematic reviews, citations on how to do systematic reviews, and a huge database of citations of clinical trials, many of them not available on MEDLINE. The Cochrane Library is available on CD-ROM and the Internet as a stand-alone resource and in other services, such as Ovid's “Evidence-Based Medicine Reviews.” If one choose not to subscribe to it, one's health sciences or hospital library likely does. Abstracts of Cochrane reviews and the abstracts of other systematic reviews (but not the rest of the library) are also available for free on the Internet at the U.K. Cochrane site (http://www.cochrane.org) and other Web sites. MEDLINE is the most likely general source to turn to when one's specific information sources fail or when one is faced with a nonroutine clinical problem. It should not be consulted first if one knows of a specific source that is current, of high quality, and tailored to the problem being dealt with, as we describe later. MEDLINE is the largest readily available database of biomedical journal citations and is now available in full or subset form for free on many Web sites, one of them produced by the U.S. National Library of Medicine (NLM). It is also more up-to-date than ever, with leading journals providing electronic copy for close to date-of-publication posting. PubMed (http://www.ncbi.nlm.nih.gov/entrez/) is the MEDLINE search interface produced by the NLM in conjunction with the U.S. National Center for Biotechnology Information. PubMed provides on-line access to literature citations and links to full-text journals at Web sites of participating publishers. (User registration, a subscription fee, or some other type of fee may be required to access the full text of articles for some journals.) PubMed also contains PREMEDLINE citations: basic citation information and abstracts are entered or downloaded daily before the full records that contain MeSH terms, publication types, and other indexing data are prepared and added to MEDLINE. Furthermore, it has a clinical query feature (http://www.ncbi.nlm.nih.gov/entrez/query/static/clinical.html) that allows a search strategy to be fine tuned using methodologic terms so that retrieval will be more clinically applicable. For example, if one's question has to do with the cause, course, diagnosis, prevention, or treatment of a clinical problem, one could go directly to the clinical query screen and indicate the study category in which one is interested and whether one would like a “sensitive” (maximal retrieval of relevant articles, with a high rate of false-positive articles) or “specific” (lower retrieval of relevant articles with fewer false positives) approach. After content words on the clinical problem of interest are entered, one proceeds with the search and complex pretested search strategies are automatically invoked, optimizing the yield of clinically relevant studies (3). In the near future, updated clinical queries will be available. These queries will be expanded from therapy, diagnosis, prognosis, and etiology to include clinical prediction guides, economics, qualitative studies, and systematic reviews (4). PubMed also has a “related articles” feature that allows the searcher to view citations related to an individual citation retrieved in a search without having to do another search. Thus, if one finds a study that is right on target, one can click on the [Related Articles] link and retrieve more articles on the same topic sorted in order of relevance. Although powerful and free, MEDLINE is not the only large biomedical database. EMBASE/Excerpta Medica and the Cumulative Index to Nursing and Allied Health Literature (CINAHL) are also available and are useful to the infection control professional in search of information. Both EMBASE and CINAHL (as well as MEDLINE) are available on the Internet through Ovid (http://www.ovid.com). Ovid provides a front-end search engine that has user fees, but many health sciences and hospital libraries provide it because it offers access to several different databases using the same user-friendly search interface and integration of database searching with a strong collection of full-text clinical journals. In addition to databases of citations to articles, Ovid provides access to books, a diagnosis program, and Evidence-Based Medicine Reviews, a multifile database that allows simultaneous searching of evidence-based medicine databases including ACP Journal Club and databases within the Cochrane Library. Case Scenario: Solving a Problem of Treatment An aggressive, bottom-line obsessed administrator in your hospital is looking for ways to save money. She requests that you consider reverting from antimicrobial-coated catheters in the intensive care unit to less expensive, uncoated catheters. She demands that you show that the coated catheters are worth their higher cost. You seek to do so as quickly as possible. Because you are pushed for time and you know that you want high-quality, patient-centered information, you start with ACP Journal Club (http://www.acpjc.org). Your initial search is effective using two words—“catheter” and “infection.” You retrieve 30 hits, most of them directly relevant. Two very relevant studies (5, 6) show that the coated catheters are effective. The systematic review by Mermel (5) showed that they are more effective than noncoated catheters and Veenstra et al. (6) provided data that showed that the coated ones are cost effective. Although the http://www.acpjc.org search was successful, it is worth taking a quick look in the Cochrane Library, another high-quality information source. You call up the Cochrane Library online, and in the “searchphrase” window you type “impregnated catheter.” There is one review in the CDSR, but it is not very relevant, because it pertains to umbilical artery catheters in newborns in the neonatal intensive care unit (7). In the Cochrane Central Register of Controlled Trials (CENTRAL), there are citations with abstracts to five randomized trials, all from 1997 to 1999. Running the search again with “coated catheter” you find no systematic reviews but 11 more randomized trials in the CENTRAL database. CENTRAL contains specialized registers of citations submitted by Cochrane groups and other organizations from many P.1641 journals and other sources that are not included in MEDLINE. Potential records from CENTRAL are assessed with quality control procedures to ensure that only reports of definite randomized controlled trials or controlled clinical trials are included. Just to make sure that you did not miss any important studies on coated catheters, you go on the Internet and pull up the clinical query option for PubMed. You pick the therapy category, select the “sensitivity” search option, and then type “impregnated central venous catheters” in the search window. You retrieve 23 citations, several of which look relevant including the already seen systematic review by Mermel (5) and the cost-effectiveness study by Veenstra et al. (6). Another method for effective clinical-based searching is to search only for articles that are clinical trials. For an article to be indexed with the publication type “clinical trial,” it must be a “preplanned, usually controlled clinical study of the efficacy, safety, or optimum dosage schedule of one or more therapeutic, diagnostic, or prophylactic drugs, devices, or techniques in humans selected according to predetermined criteria of eligibility and observed for predefined evidence of favorable and unfavorable effects” (8). The citations you retrieve using the clinical query feature in PubMed or the publication type “clinical trial” are more likely to be ready for clinical application and to help you make an informed patient-care decision than if you had not included any methodologic filtering in your search strategy. The previous scenario illustrates a search for quality-filtered prevention literature. Reports of applied clinical research have two features in common: they are designed in advance to follow a study protocol and they are comparative. Criteria exist for studies from each of the four categories of therapy and prevention, diagnosis, etiology and causation, and prognosis and natural history, as well as economic evaluations, decision analysis, quality of life, clinical utilization, reviews, guidelines, clinical prediction, and qualitative studies (9). Searching on the Internet is another route to take to help solve patient problems. However, only a small proportion of the content has been peer reviewed or provides enough information so that you can do your own evaluation on the material found. One of the most effective, and certainly the most used, search engines is Google (http://www.google.com/). No single search engine searches more than 30% to 40% of the current Web content, so a variety of search approaches may be warranted for comprehensive Internet searching. Google's search function lets you type in words or concepts of interest and then retrieves Web sites that contain these terms ranked in the order of how many other sites have linked to the original site—sort of a quality indicator. Typing in the very specific phrase “intravascular catheter infections prevention” provided access to 3,030 Web pages in 0.14 seconds. The first two link to the U.S. Centers for Disease Control and Prevention (CDC) “2002 Guidelines for the Prevention of Intravascular Catheter-Related Infections” (10). This 36-page guideline includes an analysis of previous studies and cites both the Mermel and Veenstra et al. studies along with many original studies. O'Grady et al. (10) stated that although the coated catheters are more expensive, they reduce infections and costs. All the evidence found to date seems to support the added initial expense of the coated catheters. Another approach to searching the Internet is to use one of the new question-answering systems (e.g., AskJeeves at http://www.ask.com or AnswerBus at http://www.coli.uni-sb.de/~zheng/answerbus/). Asking Jeeves “How do I prevent intravascular infections?” produced links to both U.S. and Canadian guidelines. The AnswerBus did not provide links to any site. KEEPING UP WITH THE MEDICAL LITERATURE Health professionals typically rate journal reading as their preferred means of keeping current, but more than 15 years ago, Covell et al. (11) demonstrated that this was highly overrated as a method for keeping up-to-date. Journal reading is still recommended for keeping up-to-date but with a “critical appraisal” approach, so that a reader quickly and systematically detects the original studies and reviews that are more likely to be useful to his or her practice (12). The medical literature has continued to grow at an increasing rate since the mid-1980s, so the challenge of keeping up-to-date might be considered greater than ever. However, substantial improvements have occurred in information processing as well to compensate somewhat for the increased amount of publication. We consider the journal literature first. Publishing in peer-reviewed print journals is still the most common form of spreading the word about advances in medicine, although this may change with the advent of on-line journals. ACP Journal Club, a bimonthly publication of the ACP, contains 25 structured abstracts and accompanying commentaries of original studies and systematic reviews of interest to general internal medicine, including infectious diseases. The articles, both original studies and systematic reviews, are selected from approximately 115 journals according to explicit rules of sound methodology and pertain to the treatment or prevention, diagnosis, prognosis, or etiology of disease (13). Also included are sound studies of clinical prediction, economics, differential diagnosis, and quality improvement. Following our clinical example, studies and reviews of catheter infections and their prevention have appeared several times a year in ACP Journal Club and include the Mermel and Veenstra et al. articles (5, 6). Evidence-Based Nursing is a quarterly journal published by the BMJ Publishing Group that aims to bring high quality studies and reviews to the attention of nurses attempting to keep pace with important advances in their profession. It follows a production procedure similar to that of ACP Journal Club. Evidence-Based Medicine, also published by the BMJ Publishing Group and aimed at primary care physicians, abstracts studies in family medicine, pediatrics, surgery, psychiatry and psychology, and obstetrics and gynecology, in addition to internal medicine. The abstracts for these journals are prepared by research staff with methodologic expertise and report enough information about the methods of the studies that readers can judge for themselves the strength of the research and the applicability of the findings to their own patients. Furthermore, in many instances, additional numerical results not provided in the original article are obtained or calculated and included in the abstract, such as relative risk reductions, confidence intervals, and numbers needed to treat to prevent a bad outcome or achieve a good outcome. The abstracts and commentaries P.1642 have several steps in the production process to ensure their accuracy (13). ACP Journal Club, Evidence-Based Nursing, and Evidence-Based Medicine are also available on the Web sites of their respective publishers (http://www.acpjc.org/, http://www.ebn.bmjjournals.com/, and http://www.ebm.bmjjournals.com/). ACP Journal Club is also available on Ovid in the “Evidence-Based Medicine Reviews.” MEDLINE can also be used to keep up to date, because it is updated frequently: weekly for most on-line or Internet versions and daily in the PubMed system. Searchers can thus run frequent broad-based searches to obtain the most recent citations on a topic they want to follow. “Catheter infection” might be a useful search to run weekly if one wanted to keep current with all the research on the topic. For example, on January 13, 2003 we ran this search and found another relevant guideline that had been entered into the MEDLINE system on January 9, 2003 (14). Most healthcare organizations have a “Web presence” and many have current awareness features that one can tap into to keep up to date. The Web site for the Society for Healthcare Epidemiology of America, Inc. (SHEA) (http://www.shea-online.org) is a good starting point for Web searching because it provides a page of links to other infection control sites including government (state, national, and international), other organizations, and related information resources. Furthermore, many of the various organizations have e-mail discussion lists (listservs) that one can join to receive and participate in correspondence on topics of interest. One should note that these discussion lists are anecdotal in nature and are simply exchanges of opinions among health professionals. It is up to the reader to judge the validity of individual comments. The CDC Web site (http://www.cdc.gov) provides a wide array of documents including the CDC prevention guidelines, the Morbidity and Mortality Weekly Reports, and links to many other health resources, both within the United States, including the state departments of health services, and worldwide. The CDC Web site allows searches using boolean logic in an advanced search mode (and's and or's), so that a searcher can combine words to expand or pinpoint retrieval. For keeping up to date, one can subscribe to a CDC mailing list and receive only the tables of contents or the entire documents for such items as the Journal of Emerging Infectious Diseases, human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome publications, and Morbidity and Mortality Weekly Report. The Division of Healthcare Quality Promotion provides information on the prevention and control of nosocomial infections (http://www.cdc.gov/ncidod/hip). It has guidelines, recommendations, and answers to frequently asked questions on topics such as outbreaks, occupational exposure to HIV, needlestick injuries, and child care. Of note is their “2002 Guideline for Prevention of Intravascular Catheter-Related Infections” (http://www.cdc.gov/ncidod/hip/IV/IV.HTM) already identified in our Internet search. The CDC Web site also indicates which documents have recently been added and which are expected soon. It ranks its top challenge as reducing catheter-associated adverse events by 50% among patients in healthcare settings. The Web site for the Hospital Infection Society (http://www.his.org.uk) in the United Kingdom includes the abstracts of articles in the Journal of Hospital Infection, lists future scientific meetings, and has an e-mail discussion list. The Web site for the Faculty of Medicine at Università Catholique de Louvain in Brussels (http://www.md.ucl.ac.be/entites/esp/hosp/infcon.htm) has a database of many hundreds of selected articles with abstracts in the area of infection control that is updated quarterly. It also links to journals on infection control and hospital epidemiology for scanning tables of contents to identify potentially relevant citations. The Association for Professionals in Infection Control and Epidemiology (APIC) has a Web site (http://www.apic.org) that updates professionals about courses and educational activities, upcoming conferences, and publications (such as the APIC Text of Infection Control) that can be ordered from the Internet. Professional resources provided on the APIC Web site include a discussion forum in which infection control professionals can discuss issues with each other; find or list job postings; and access a resource list, a searchable abstract database, and an open e-mail list server. The Program for Monitoring Emerging Diseases (ProMED) (http://www.fas.org/promed) is a free electronic conferencing system formed by the Federation of American Scientists to create a global system of early detection and response to disease outbreaks. It also has a search engine for archived e-mail correspondence. Individual clinicians can keep in touch with a variety of health organizations through Web sites as an increasing number of organizations post their latest information on the Internet. By subscribing to some of the many list servers and discussion lists of the aforementioned organizations, one can participate in real time discussions on topics of interest, and current information such as the latest journal contents or knowledge of outbreaks comes automatically. Unfortunately, for most of these services, one will need to do an assessment of the validity and relevance of the information. The relevance check is pretty easy, but checking the sources for scientific merit requires skill and time. Several of the aforementioned resources are now available in a format for the latest in computer gadgetry: the handheld or PDA. PDAs have been embraced by many in the medical community, because they can store surprisingly large amounts of information and can be used in any location by virtue of their small size and portability (15, 16). Many sources of information exist for clinicians interested in PDAs and one such site is Evidence-Based Medicine Tools for the PDA (http://www.ils.unc.edu/~caham/ebmtools/ebmtools.html). Categories of applications and services include drug information (especially ePocrates http://www.epocrates.com/), news and abstracting services, healthcare literature summaries and full text, guidelines and summaries, textbook information, diagnostic aids, statistical and numerical calculators, and clinical prediction guides. A listing of available resources in this chapter would not be very helpful because of the rapid rate of change, so we urge those who are interested in acquiring a PDA to consult peers and use the Internet to learn about and acquire clinical resources for downloading. SETTING CLINICAL POLICY Clinical practice guidelines have metamorphosed from their first appearance on the healthcare stage, as small local health plans or care maps developed to reduce variability in care, into a healthcare industry. Practice guidelines have become ubiquitous P.1643 and are promoted for a number of reasons, including improving the quality of healthcare, optimizing patient outcomes, discouraging the use of ineffective or harmful interventions, improving the consistency of care, identifying gaps in evidence, helping to balance costs and outcomes, or simply cutting costs. Clinical practice guidelines for screening, diagnosis, prevention, and treatment are produced by diverse organizations, from government departments (such as the U.S. Agency for Healthcare Research and Quality or the CDC), healthcare associations and specialty societies (such as the American College of Physicians, the Society for Healthcare Epidemiology of America, and the Infectious Disease Society of America), and local hospitals. The definition from the Institute of Medicine in 1990 (17) still applies, however, at all levels: “Practice guidelines are systematically developed statements to assist practitioner and patient decisions about appropriate healthcare for specific clinical circumstances.” Three useful Internet sites that list guidelines are the National Guideline Clearinghouse (http://www.guideline.gov/index.asp), Agency for Healthcare Research and Quality (http://www.ahcpr.gov/clinic/cpgsix.htm), and the Canadian Medical Association (http://www.cma.ca/cma/common/displayPopup.do?tab=422&=125&pMenuId=4). The first site, the U.S. National Guideline Clearinghouse, is a valuable site for access to almost any local, regional, national, or international guideline. It not only lists guidelines and provides access to the full text of many but also has the capability of comparing two guidelines in a tabular format. Infection control is particularly suited to the use of clinical practice guidelines. If based on sound current evidence, guidelines can greatly reduce the amount of work of infection control specialists in searching the literature. Guidelines published in the journal literature are searchable in MEDLINE by using the publication type field “guideline” for administrative procedural guidelines and “practice guideline” for specific healthcare guidelines. The Internet is also an excellent source in which to locate guidelines, particularly because the entire document is usually posted on the Web site, whereas in MEDLINE only the citation and possibly the abstract to the document is available. The Future Health Care Web site (http://www.futurehealthcare.com/pages/guidetobestpractices.htm) is particularly useful for helping to define “best practices” for quality assurance activities (18). We have already identified a recent and relevant clinical practice guideline on our intravascular coated catheters (10) so we will identify any more, although several less recent ones exist. CONCLUSIONS To conclude our clinical scenario, you give your administrator the data you find. She is duly impressed with your evidence that the more expensive coated catheters are actually saving the hospital money and reducing infections. She thanks you and as you return to your office and mentally review your information trek. You wonder if this is just the first of many such evidence assessments you will be asked to perform. Persons involved with hospital epidemiology and infection control have many diverse information needs that include medical and other health-related clinical materials, basic science information, management and educational resources, and policy documents from regional and national agencies. Today, clinicians are working in a rapidly changing environment with new discoveries, scarce resources, and new challenges presented by the changing model of healthcare delivery, multiresistant microorganisms, emerging pathogens, and outbreak detection. To succeed, one must develop rapid and efficient ways of acquiring new relevant information. By investing time in experimenting with the different resources available, one will be able to develop an individual strategy for dealing with new clinical problems, keeping up-to-date, and effectively implementing new policies. Clinicians are indeed fortunate that as the need for information increases, the means for acquiring it continue to evolve and improve. REFERENCES 1. Sackett DL, Straus SE, Richardson WS, et al. Evidence-based medicine: how to practice & teach EBM, 2nd ed. Edinburgh: Churchill Livingstone, 2000. 2. Richardson WS, Wilson MC. Textbook descriptions of disease—where's the beef? [editorial]. ACP J Club 2002 Jul–Aug; 137:A11–A15. 3. Haynes RB, Wilczynski N, McKibbon KA, et al. Developing optimal search strategies for detecting clinically sound studies in MEDLINE. J Am Med Inform Assoc 1994;1:447–458. 4. Wilczynski NL, Haynes RB. Robustness of empirical search strategies for clinical content in MEDLINE. Proc AMIA Symp 2002; 904–908. 5. Mermel LA. Prevention of intravascular catheter-related infections. Ann Intern Med 2000;132:391–402. 6. Veenstra DL, Saint S, Sullivan SD. Cost-effectiveness of antiseptic-impregnated central venous catheters for the prevention of catheter-related bloodstream infection. JAMA 1999;282:554–560. 7. Barrington KJ. Umbilical artery catheters in the newborn: effects of catheter materials. Cochrane Review [updated 18 Nov 1998]. In: The Cochrane library. Oxford: Update Software. 8. National Library of Medicine. Medical Subject Headings, Annotated Alphabetic List. 1998. Distributed by the National Technical Information Service, U.S. Department of Commerce. PB98-964801. 9. Guyatt G, Rennie D, eds. The Evidence-Based Medicine Working Group. Users' guides to the medical literature: a manual for evidence-based clinical practice. Chicago, 2002. 10. O'Grady NP, Alexander M, Dellinger EP, et al. Guidelines for the prevention of intravascular catheter-related infections, 2002. MMWR Morb Mortal Wkly Rep 2002;51:RR-10 available at http://www.cdc.gov/ncidod/hip/IV/IV.HTM (accessed). 11. Covell D, Uman G, Manning P. Information needs of office practice: are they being met? Ann Intern Med 1985;103:596–599. 12. Sackett DL, Haynes RB, Guyatt GH, et al. Clinical epidemiology: a basic science for clinical medicine, 2nd ed. Boston: Little, Brown and Company, 1991. 13. Sackett DL, Haynes RB. 13 steps, 100 people, and 1,000,000 thanks [editorial]. ACP J Club 1997 Jul–Aug; 127:A14. 14. O'Grady NP, Alexander M, Dellinger EP, et al. Guidelines for the prevention of intravascular catheter-related infections. Infect Control Hosp Epidemiol 2002;23:759–769. 15. Richardson WS, Durdette SD. Practice corner: taking evidence in hand [editorial]. ACP J Club 2003 Jan–Feb; 138:A12. 16. Rao G. Introduction of handheld computing to a family practice residency program. J Am Board Fam Med 2002;15:118–122. 17. Field MJ, Lohr KN. Clinical practice guidelines. Washington, DC: National Academy Press, 1990. 18. Kibbe DC, Smith PP, LaVallee R, et al. A guide to finding and evaluating best practices health care information on the Internet: the truth is out there? Jt Comm J Qual Improv 1997;23:678–689.
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Nosocomial infections may be caused by community microorganisms brought into the hospital by patients or others, or by hospital microorganisms that are infecting or colonizing patients or staff members or contaminating the inanimate environment. To be successful as hospital pathogens, nosocomial bacteria must be able to establish themselves and survive in the hospital environment, colonize the mucosa and skin of patients and staff members, survive on various surfaces during patient-to-patient transmission, and resist antibiotic and sometimes antiseptic therapy (1). Inherent multiple antibiotic resistance, and the ability to acquire additional genetic resistance factors in the face of increasing use of antibiotics, is important for survival. Numerous reports show that microorganisms causing hospital infection and colonizing patients and staff members are more antibiotic-resistant than those in the community. For example, human fecal bacteria are more resistant in hospital populations than such bacteria outside. Acquired antibiotic resistance was rare in Escherichia coli isolated from the feces of animals and humans in remote areas of the world before the introduction of antibiotics (2, 3), and in London in the 1960s antibiotic resistance was uncommon in fecal microorganisms but increased in patients after they were admitted to the hospital (4). Similarly, fecal microorganisms in hospital sewage were found to be more antibiotic-resistant than those from domestic sewage (5), and antibiotic resistance and multiple resistance increased in sewage microorganisms in outflow from a new hospital in Hong Kong soon after it opened but did not change in microorganisms in sewage from a nearby town (6). The assessment of antibiotic resistance in hospital bacterial isolates has been hampered by a lack of agreement on how resistance rates should be measured. Artificially high rates may be produced by counting multiple isolates of the same resistant microorganism from the same patient or from different patients during outbreaks. However, it has now been shown that results from the first isolate only of a bacterial species per patient give acceptable antimicrobial susceptibility rates that can be used for comparative purposes (7, 8, 9). National resistance rates are often extrapolated from surveillance data derived from a few hospitals in a few centers, with little attention to the use of appropriate denominators. Despite these reservations, we believe resistance is increasing, but the exact levels of resistance in different places and the rate of increase are unclear. The situation is further complicated by the high rates of hospital-acquired infection and antimicrobial resistance in intensive care units (ICUs). Indeed, laboratory-based resistance rates for all microorganisms in the ICU are the same as rates based on epidemiologic surveillance of hospital-acquired infections only (10). Archibald et al. (11) demonstrated that there was a significant stepwise decrease in the percentage of resistant microorganisms isolated from patients in the ICU, from non-ICU inpatients, and from outpatients. They concluded that resources allocated to control antimicrobial resistance therefore should be concentrated on the hospital and particularly on the ICU. A number of surveillance systems studying hospital-acquired infection and antimicrobial resistance have been set up, including the U.S. Intensive Care Antimicrobial Resistance Epidemiology (ICARE) Project (10) and the European Prevalence of Infection in Intensive Care (EPIC) Study (12). In January 1999, the hospital-wide component was eliminated from the National Nosocomial Infections Surveillance (NNIS) system, because case finding was costly and inaccurate, and rates were unhelpful for national comparison, because they were not risk-adjusted. Perhaps as a reflection of this, the pooled NNIS antimicrobial resistance rates for various nosocomial pathogens for the decade of 1992–2002 show little difference between ICU and non-ICU patients (Table 91.1). The experience of many clinicians supports the view of Archibald et al. (11) that rates are higher in ICU. TABLE 91.1. POOLED MEANS OF THE DISTRIBUTION OF ANTIMICROBIAL RESISTANCE RATES (%), BY ALL ICUs COMBINED AND NON-ICU INPATIENT AREAS, JANUARY 1998 TO JUNE 2002 Pathogen ICUs Non-ICUs MRSA 51.3 41.4 Methicillin-resistant CNS 75.7 64.0 Vancomycin-resistant Enterococcus spp. 12.8 12.0 Ciprofloxacin/ofloxacin-resistant Pseudomonas aeruginosa 36.3 27.0 Levofloxacin-resistant P. aeruginosa 37.8 28.9 Imipenem-resistant P. aeruginosa 19.6 12.7 Ceftazidime-resistant P. aeruginosa 13.9 8.3 Piperacillin-resistant P. aeruginosa 17.5 11.5 Cef3-resistant Enterobacter spp. 26.3 19.8 Carbapenem-resistant Enterobacter spp. 0.8 1.1 Cef3-resistant Klebsiella pneumoniae 6.1 5.7 Cef3-resistant Escherichia coli 1.2 1.1 Quinolone-resistant E. coli 5.8 5.3 Penicillin-resistant pneumococci 20.6 19.2 Cefotaxime/ceftriaxone-resistant pneumococci 8.2 8.1 MRSA, Methicillin-resistant Staphylococcus aureus; CNS, coagulase-negative staphylococci; Cef3, ceftazidime, cefotaxime, or ceftriaxone; Quinolone, ciprofloxacin, ofloxacin, or levofloxacin; Carbapenem, imipenem or meropenem. From National Nosocomial Infections Surveillance (NNIS) System Report, data summary from January 1992 to June 2002, issued August 2002. Am J Infect Control 2002;30:458–475. Table 91.2 shows results from the NNIS system comparing resistance rates in U.S. ICUs for various pathogens isolated in 1994–1998 and 1999 (13). It can be seen that during this period there was a dramatic increase in resistance rates for several important nosocomial pathogens. In particular there was a 47% increase in vancomycin resistance in enterococci, a 43% increase in methicillin resistance in Staphylococcus aureus, and an increase in resistance in Pseudomonas aeruginosa of 35% and 49% to imipenem and quinolones, respectively. TABLE 91.2. MEAN RESISTANCE RATES IN SELECTED PATHOGENS ASSOCIATED WITH NOSOCOMIAL INFECTIONS IN ICU PATIENTS, JANUARY-MAY 1999 COMPARED WITH THE FIVE YEARS 1994–1998 Antimicrobial/Pathogen Increase in Resistance(%) Vancomycin/enterococci 47 Methicillin/Staphylococcus aureus 43 Methicillin/coagulase-negative staphylococci 2 3rd cephalosporin/E. coli 23 3rd cephalosporin/K. pneumoniae -1 Imipenem/P. aeruginosa 35 Quinolone/P. aeruginosa 49 3rd cephalosporin/P. aeruginosa <1 3rd cephalosporin/Enterobacter spp. 3 3rd, third generation. From National Nosocomial Infections Surveillance (NNIS) System Report. Data Summary from January 1990-May 1999, Issued June 1999. Am J Infect Control 1999;27:520–532. P.1614 Until recently, typing methods for nosocomial bacteria were usually clumsy, imprecise, or, for many species, unavailable. However, the introduction of genome analysis has provided relatively simple and greatly improved methods for elucidating the epidemiology of most microorganisms of hospital infection (14, 15, 16). Similarly, the epidemiology of antibiotic resistance was previously based on phenotypic descriptions. Now that we have a better understanding of the molecular basis of resistance and genetic probes for resistance determinants are more widely available, the molecular epidemiology of resistance genes is becoming clearer (17). EMERGENCE OF ANTIBIOTIC RESISTANCE IN NOSOCOMIAL PATHOGENS Antibiotic Use and Antibiotic Resistance Hospital patients often have compromised host defenses due to treatment or underlying disease, and therefore are at risk of acquiring infection with both virulent and opportunistic pathogens. Since antibiotic use is concentrated in hospitals, both types of pathogen are more likely to survive and proliferate in the hospital environment and colonize patients if they are resistant to common antimicrobials. Furthermore, infection with resistant microorganisms often fails to respond to initial empirical therapy, increasing the time during which cross-infection may occur. Antimicrobial resistance is thus one of the factors that favor the development of hospital infection, and at any given time the common nosocomial pathogens are often resistant to the antibiotics in current use. The tendency for antibiotic use to promote the emergence of resistant pathogens is called “antibiotic pressure.” The relationship between antibiotic use and antibiotic resistance, and the problems of proving a cause-and-effect relationship, have been well reviewed by McGowan (18). Despite methodologic difficulties, there are many reports of resistance rising during increased antibiotic use and falling after a reduction in use (18). Nevertheless, as McGowan points out, antibiotic pressure is not the only reason why nosocomial pathogens appear increasingly antibiotic-resistant. Publication Bias Unusual antimicrobial resistance is a simple and readily available epidemiologic marker for hospital infection. The appearance of urinary tract infection caused by cephalosporin- and aminoglycoside-resistant Klebsiella pneumoniae, for example, will be vigorously pursued by the infection control team and perhaps reported in the literature, whereas a similar outbreak with a sensitive strain may go unnoticed and unreported. The tendency of authors to report, and editors to accept, accounts of infection caused by multiply resistant rather than sensitive microorganisms is an example of publication bias (18). Thus, although nosocomial pathogens are usually multiply antibiotic-resistant, this characteristic is sometimes overemphasized. Opportunistic Infection and Antibiotic Resistance With advances in medical care, many highly compromised patients are being successfully treated by intensive medical care but remain vulnerable to nosocomial infection. Immunocompromised patients are susceptible to opportunistic pathogens of low virulence, and those undergoing intensive therapy may become infected by free-living bacteria that survive in the hospital environment and are transmitted to patients via equipment such as ventilators and urinary and vascular catheters. These opportunists are often inherently resistant to common antibiotics, probably because they are adapted to live in soil and water, where they are exposed to naturally occurring antimicrobial substances. They are also relatively resistant to disinfectants and can be selected P.1615 by changing patterns of disinfectant use. These microorganisms include Pseudomonas, Acinetobacter, and Enterobacter species, which would have become increasing causes of hospital infection even without antibiotic pressure. The coagulase-negative staphylococci, which colonize human skin and are often antibiotic-resistant, rarely, if ever, cause infection in healthy individuals but have become major causes of nosocomial bloodstream infection, because they can adhere to prosthetic implants and vascular catheters. All these inherently resistant microorganisms also tend to acquire further antibiotic resistances in hospitals, encouraged by antibiotic pressure. The emergence of gram-positive nosocomial pathogens, such as the enterococci, is probably directly related to their inherent resistance to the cephalosporins, aminoglycosides, and quinolones during a period of increasing use of these drugs for the treatment of gram-negative infections. Environmental Contamination and Antibiotic Resistance Many gram-negative opportunistic pathogens are free-living, nonfastidious in their nutritional requirements, and capable of multiplying at a wide range of temperatures. They can survive and proliferate in wet environmental sites such as hospital water systems (19, 20, 21, 22, 23, 24), and sink drains (25, 26, 27), and may sometimes spread from these reservoirs to cause infections in patients. These water microorganisms include a number of nonfermenting bacteria, such as Pseudomonas, Acinetobacter, and Flavobacterium species, which are inherently antibiotic-resistant and can accumulate acquired resistance factors. Pseudomonas fluorescens can grow at 48ВC and has caused several outbreaks of bacteremia following contamination of refrigerated blood transfusion packs (28). Resistant Enterobacteriaceae and gram-positive microorganisms are also sometimes isolated from these environmental sites; for example, Enterobacter cloacae has been isolated from ice machines (21) and coagulase-negative staphylococci causing prosthetic valve endocarditis from ice-water baths used during thermodilution cardiac output studies (29). Similarly, outbreaks of disinfectant- and antibiotic-resistant pseudomonads have been reported, associated with contamination of the internal plumbing of endoscope washer-disinfectors (30, 31). Multiresistant gram-negative bacteria such as Pseudomonas, Burkholderia, Stenotrophomonas, Ralstonia, Acinetobacter, Enterobacter, Klebsiella, Citrobacter, Serratia, and Flavobacterium species may also contaminate and survive in supposedly sterile solutions or clean-water reservoirs associated with hospital equipment. Outbreaks of antibiotic-resistant infection may thus occur when there are failures of sterilization of injectable solutions or breakdowns in the maintenance, decontamination, and disinfection of equipment. For example, a Pseudomonas species established itself in the distilled water supply of a hospital pharmacy and contaminated sterilized infusion fluids when the distilled water was used to cool autoclaved bottles (19). Compared with other Enterobacteriaceae, Enterobacter species have a special ability to survive and multiply in 5% dextrose solutions (32) and have caused a number of outbreaks of bacteremia following infusion of contaminated fluids (33, 34). Outbreaks due to many different multiresistant gram-negative bacteria have been associated with contaminated hospital equipment such as arterial pressure monitoring systems (35, 36), endoscopes (37), suction apparatus, humidifiers, nebulizers, ventilators, and breast pumps (38, 39). Similarly, resistant microorganisms such as Klebsiella, Serratia, and Enterobacter species may contaminate and survive in cold hospital food or enteral feeds given to compromised patients (40, 41). Free-living, multiply resistant, gram-negative microorganisms tend to be relatively resistant to disinfectants and bacteriostatic agents. Thus, contamination of disinfectants and multiple-use medications may lead to outbreaks of antibiotic-resistant infection. P. aeruginosa, for example, is so resistant to the quaternary ammonium compounds that cetrimide is used in a Pseudomonas-selective culture medium! Many strains of methicillin-resistant S. aureus (MRSA) and methicillin-resistant Staphylococcus epidermidis acquire genes for resistance to disinfectants such as cetrimide and chlorhexidine disinfectants, which may facilitate the spread of these microorganisms in hospitals (42, 43). McGowan (44) has emphasized, however, that the environment is rarely the reservoir for endemic hospital infection and only occasionally acts as the source for individual outbreaks. Furthermore, environmental sites may become contaminated from infected or colonized patients rather than the other way around. Routine surveillance cultures of the hospital environment, therefore, are unjustified, and environmental cultures made during outbreaks should be interpreted with care (44, 45). MECHANISMS AND GENETICS OF ANTIBIOTIC RESISTANCE Some microorganisms are inherently resistant to common antimicrobials. For example, K. pneumoniae is resistant to ampicillin; Enterobacter species to ampicillin and many cephalosporins; enterococci to cephalosporins and quinolones; and P. aeruginosa to ampicillin, some cephalosporins, and other groups. Some Pseudomonas species are inherently resistant to nearly all of the agents active against gram-negative bacteria, the JK coryneforms are resistant to most drugs used for gram-positive infection, and fungi such as Candida albicans are inherently resistant to all antibacterial antibiotics. Antibiotic therapy tends to suppress sensitive environmental and commensal bacteria and encourage their replacement with resistant microorganisms. Initially, the more resistant members of generally sensitive species proliferate, and then the inherently resistant genera take over. Highly compromised patients who receive multiple courses of antibiotics commonly become colonized by increasingly resistant microorganisms, often suffering sequential infections with Klebsiella, P. aeruginosa, enterococci, and, finally, Candida. Naturally sensitive bacteria may acquire antibiotic resistance caused by a number of mechanisms (46, 47). The most common is probably the production of drug-destroying enzymes. This is the typical mechanism by which microorganisms such as S. aureus and E. coli and other gram-negative bacteria acquire resistance to ampicillin, aminoglycosides, and chloramphenicol. There may be alterations in the permeability of the cell wall, preventing antibiotics from reaching their target sites (or there may be increased antibiotic efflux, resulting in the same effect). P.1616 This is the common mechanism of tetracycline resistance and is one of the ways in which microorganisms such as P. aeruginosa may acquire resistance to several aminoglycosides simultaneously. Alterations in target sites prevent antibiotics from binding at their sites of action. Changes in the affinities of penicillin-binding proteins result in methicillin resistance in staphylococci, penicillin resistance in pneumococci, and ampicillin resistance in enterococci. Alterations in ribosomal-binding sites may produce acquired resistance to rifampin, fusidic acid, and the macrolides, and alteration of DNA gyrase is the common mechanism of quinolone resistance. Alterations (or substitutions) of enzymes in metabolic pathways are responsible for resistance to sulfonamides and trimethoprim that block bacterial folate metabolism. Acquired resistance mechanisms may be encoded on the bacterial chromosome or on plasmids, which are independently replicating molecules of extrachromosomal DNA. Resistance may emerge by mutation, which occurs relatively frequently in rapidly multiplying bacteria, or, more commonly, by acquisition of resistance plasmids from other bacteria. The spread of resistance among bacteria by plasmid transfer is sometimes called “infectious resistance.” The transmission of DNA between bacteria may occur by bacteriophage transduction (as in the transmission of penicillinase-mediated penicillin-resistance in S. aureus), conjugation (the common mechanism of transfer between gram-negative species), or transformation. Transformation was previously regarded as a relatively unimportant mechanism of resistance transfer in clinical bacteria, but there is increasing evidence for its importance in the emergence of resistance in gram-positive microorganisms. Although the host range of many plasmids is restricted, and gram-positive and gram-negative microorganisms tend not to share resistance genes, plasmids can be exchanged between different bacterial species; for example, most ampicillin resistance in Haemophilus influenzae is mediated by a ОІ-lactamase that probably originated from E. coli. Resistance genes may be encoded on a variety of transferable elements, including transposons and integrons that can insert into both chromosomes and plasmids. The combination of multiple insertion elements may create large multiple resistance gene packages (48). Integrons encoding multiple antimicrobial resistances are now widespread in Enterobacteriaceae in both hospitals and the community (49, 50). There is continuous horizontal transfer of these resistance genes between and within species, and acquisition of multiple resistance favors the proliferation of certain cross-infecting microorganisms in hospitals (51). The spread of resistance plasmids or transposons among several different bacterial strains or species may produce an epidemic of resistance in commensal and environmental bacteria during an outbreak of hospital infection in patients (52, 53, 54). Klebsiella and Serratia species are particularly good at acquiring and disseminating a variety of resistance plasmids (55, 56, 57, 58). Opportunistic pathogens such as these, which can readily acquire new resistances in the face of changing therapy, have become the dominant causes of hospital infection. THE CHANGING PATTERN OF HOSPITAL INFECTION The use of antibiotics encourages the development of more resistant bacteria in patient commensal flora and in the hospital environment (4, 59, 60, 61, 62), leading to antibiotic-resistant hospital-acquired infection. After effective therapy is introduced for one group of such infections, there is a tendency for another group of resistant microorganisms to emerge. A change in pattern of serious hospital infection after the introduction of antibiotics was first noted by Finland and his colleagues (63). Between 1935 and 1957, antibiotic-sensitive gram-positive pathogens were replaced by penicillin-resistant S. aureus and multiresistant gram-negative bacteria such as E. coli, Klebsiella, and Proteus species. As discussed previously, these gram-negative opportunists emerged not only because they are inherently resistant to common antimicrobials and disinfectants, but also because many of them are free-living microorganisms that can survive in wet sites in the hospital environment (22, 25, 26, 27, 64, 65). Once the emergence of resistant opportunistic pathogens had been recognized, new, more effective drugs were developed for therapy. The worldwide problem of the multiresistant “hospital staphylococcus” in the 1960s diminished after the introduction of methicillin, oxacillin, and cloxacillin (66, 67), and outbreaks of gentamicin-resistant Klebsiella and other gram-negative microorganisms seen in the 1970s waned in the 1980s with the use of newer aminoglycosides and cephalosporins. Since the 1980s, however, the pattern has changed again with a dramatic increase in multiply resistant gram-positive nosocomial infection (1, 68). Methicillin-resistant S. aureus, resistant to all ОІ-lactams and to many other previously effective agents, has emerged as a worldwide cause of large hospital outbreaks associated with serious morbidity and mortality (66, 67, 69, 70). Coagulase-negative staphylococci are increasingly common hospital pathogens (71), partly because they, too, are often resistant to methicillin and other agents, but also because many strains produce an extracellular slime (72, 73, 74) that enables them to colonize intravascular and other plastic prostheses. Finally, many antibiotics used for gram-negative nosocomial infections, including ampicillin, the aminoglycosides, cephalosporins, and quinolones, are ineffective against coryneform bacteria and enterococci, and therefore these species have also emerged as important causes of hospital infection (75). This is a continuing dynamic situation. Resistant gram-positive bacteria remain a major feature of hospital infection, mainly because of widespread endemic MRSA. However, resistant gram-negative bacteria continue as important nosocomial pathogens, usually causing epidemics or sporadic endogenous infection. Thus the picture now is of hospital infection being dominated by multiply drug resistant (MDR) pathogens of multiple species and gram-reaction. Since fungi such as Candida and Aspergillus species are resistant to virtually all antibacterials; multiple courses of therapy in highly compromised patients may result in colonization and infection with these microorganisms. However, because fungi have always been inherently resistant to antibiotics, and serious invasive infection usually occurs only in patients with deficiencies of cell-mediated immunity, changes in antibiotic use have probably had little effect on the incidence of such infections, which account for only a few percent of all nosocomial episodes (71). Multiresistant aerobic gram-positive bacteria were responsible P.1617 for 39% of all nosocomial infections analyzed by the U.S. NNIS system between January 1990 and March 1996 (76). Aerobic gram-negative bacteria caused 42% of infections during the same period. S. aureus was the commonest isolate of all, followed by E. coli, coagulase-negative staphylococci, and Enterococcus species. Coagulase-negative staphylococci were the most common microorganisms isolated from blood and enterococci the second most common from urine (after E. coli). Gram-positive bacteria were also frequently isolated from ICU patients studied between January 1986 and April 1997 (77), where they were found in 50% of positive blood cultures and 39% of infected wounds. MULTIRESISTANT PROBLEM MICROORGANISMS Gram-Negative Bacteria Escherichia coli Escherichia coli is the commonest cause of hospital-acquired gram-negative urinary tract infection and septicemia (71). The species is naturally susceptible to ampicillin, but now about 50% to 60% of both hospital and community isolates are resistant (78), usually by the production of ОІ-lactamases, enzymes that bind and destroy ОІ-lactam antibiotics. The most common type of ОІ-lactamase in E. coli is TEM-1, accounting for about 80% of such resistance (79, 80, 81). TEM-1 is encoded on transferable plasmids and has disseminated throughout the world since its discovery in 1965 (82). Some strains of Enterobacteriaceae, including E. coli, produce TEM-2, a similar enzyme that differs from TEM-1 only in a single amino acid. Although ampicillin is now unreliable for the treatment of E. coli infection, other drugs usually remain effective, including the cephalosporins, quinolones, and aminoglycosides. E. coli can also be treated by the combination of a ОІ-lactam with a ОІ-lactamase inhibitor, such as amoxicillin/clavulanic acid (co-amoxiclav) and ampicillin/sulbactam. The ОІ-lactamase inhibitors prevent the action of TEM-1 or TEM-2 and restore the activity of the ОІ-lactams. This combination is now threatened, because some E. coli strains can produce excessive amounts of TEM-1 that swamp the effect of the ОІ-lactamase inhibitor (83, 84) or are resistant to it (81). Mutations in TEM-1 and TEM-2 have resulted in new “extended-spectrum” ОІ-lactamases (ESBLs) that can break down newer cephalosporins and thus render E. coli resistant to them. These ESBLs are named TEM-3, TEM-4, etc., and more than 100 of them have been reported (46, 85). They are often plasmid-borne and associated with other multiple resistances such as aminoglycoside resistance. However, E. coli is not a very epidemic microorganism in hospitals, and hospital outbreaks are more common with ESBL-producing strains of K. pneumoniae (see below). Nevertheless, cephalosporin resistance is increasing in hospital isolates of E. coli, and in the U.S. NNIS system, resistance to newer cephalosporins in ICU isolates of E. coli increased 23% between 1994–1998 and 1999 (Table 91.2) (13). E. coli can acquire other resistances, including plasmid-borne aminoglycoside resistance and, increasingly, mutational quinolone resistance, but their frequencies vary considerably in different parts of the world (86, 87, 88). In the European Antimicrobial Resistance Surveillance System (EARSS) study from 2001, resistance to gentamicin was less than 5% in most European countries but was more than 10% in Israel, Bulgaria, and Malta. In ten of the 20 countries surveilled by EARSS, ciprofloxacin resistance was more than 8%, and ranged between 0% (Estonia) and 21% (Israel) (87). E. coli is relatively fastidious in its nutritional requirements and does not survive well in the environment. For these reasons, most nosocomial E. coli infections are endogenous, arising from commensal bowel flora (89), and they are relatively easy to treat. However, a few outbreaks of hospital and community infection with multiresistant strains have been reported (90, 91). Klebsiella, Enterobacter, and Serratia Species Klebsiella, Enterobacter, and Serratia species are common opportunistic pathogens that have similar epidemiologies and clinical presentations. They are all inherently resistant to ampicillin, and Enterobacter species and Serratia species are resistant to first-generation cephalosporins (78). These enterobacteria have a great facility for acquiring and disseminating resistance plasmids (54, 58, 92, 93), especially among themselves, and Enterobacter species may develop chromosomal resistance to newer cephalosporins (94, 95). To a greater or lesser extent, they colonize human bowel and patient skin and may spread from person to person on staff members' hands. They may then go on to colonize the urinary and respiratory tracts of patients treated with ОІ-lactams and may produce bacteremia in the immunocompromised host. They are relatively free-living and can also survive and multiply in nutritionally poor wet environments at room temperatures. Because of this, they may contaminate food, enteral feeds, and infusion fluids, leading to widespread common-source outbreaks. Klebsiella Species K. pneumoniae is naturally resistant to ampicillin, usually by the production of SHV-1, a ОІ-lactamase similar to TEM-1 and TEM-2, which may be encoded on either the chromosome or, less commonly, on a transferable plasmid (96). Because of this natural resistance, K. pneumoniae often replaces commensal E. coli in patients treated with ampicillin or similar drugs. The carriage rate in normals is low but increases in hospitalized patients, especially during prolonged hospitalization or antibiotic therapy (97, 98). The microorganism can colonize the bowel, the bladder, the upper respiratory tract, and the skin and, in compromised patients, may go on to produce invasive urinary and respiratory tract infection and septicemia. Most colonized patients are asymptomatic, but they may act as sources of cross-infection for others; the outbreak strain is usually transferred on staff members' hands (99, 100, 101). In addition, K. pneumoniae readily acquires other transferable resistances and disseminates them to other strains of Klebsiella or other species of Enterobacteriaceae (40, 53, 54). K. pneumoniae (and Enterobacter species) appear to have a greater ability than E. coli and other Enterobacteriaceae to colonize the skin of patients and to survive on both skin and dry surfaces (89, 92, 97, 98, 101). On dry surfaces, about 10% of E. coli but only 1% of Klebsiella lose plasmid-mediated P.1618 gentamicin resistance (89). All these factors contribute to the success of Klebsiella species as opportunistic hospital pathogens. During the 1970s, there were frequent reports of hospital outbreaks of gentamicin-resistant K. pneumoniae, sometimes associated with significant mortality when highly compromised patients were involved (102, 103, 104, 105). The microorganisms often spread between hospitals and into the community. They became endemic in some hospitals and were sometimes associated with the simultaneous appearance of multiple resistances in other strains of Klebsiella and in other species of Enterobacteriaceae (55, 106, 107). In these cases, K. pneumoniae appeared to be acting as an engine of resistance dissemination, especially resistance to aminoglycosides (40, 92). Once the epidemiology of resistant Klebsiella infection was understood, and following the introduction of newer cephalosporins, these outbreaks became much less common. However, strains of K. pneumoniae (and also Klebsiella ozaenae) have appeared that are resistant to third-generation cephalosporins and can spread to produce hospital outbreaks (85, 108, 109, 110, 111). This type of resistance is mediated by the production of ESBLs that can break down some of the newer cephalosporins. These ОІ-lactamases are the result of small mutations in the genes encoding TEM-1, TEM-2, or SHV-1 (46, 85), although other families of enzymes may be involved (46, 80). They are encoded on plasmids that can transfer to other species, and they are often associated with other multiple resistances, including resistance to aminoglycosides (112). Although ESBL-producing strains are usually susceptible to ОІ-lactam–β-lactamase-inhibitor combinations such as amoxicillin plus clavulanate and ampicillin plus sulbactam, nosocomial isolates may be resistant by hyperproduction of the ESBL (113, 114). These multiresistant strains may also acquire resistance to quinolones by mutation. Thus, recent isolates are often resistant to all the common ОІ-lactams, aminoglycosides, and quinolones, and reliably susceptible only to the carbapenems. Outbreaks with these new multiresistant Klebsiella species seem to have an epidemiology similar to that of the gentamicin-resistant Klebsiella outbreaks of the 1970s. They can cause large hospital outbreaks, sometimes with dissemination between hospitals (115), and the outbreak strains can pass aminoglycoside and cephalosporin resistances to other bacterial species (116). Initially these new multiply-resistant Klebsiellas were seen sporadically in Europe (108, 109, 110), but much larger outbreaks have been reported from many countries around the world (113, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127). These microorganisms are also causing sporadic infections with increasing frequency: in a survey of 35 European ICUs, ESBL producers accounted for 23% of 966 sequential Klebsiella isolates (128). Klebsiella oxytoca has been shown by DNA hybridization to be a distinct species of Klebsiella and may even belong in a different genus (129). It is a less common cause of human infection than K. pneumoniae but has emerged as an important nosocomial opportunist that also can produce and disseminate resistance to aminoglycosides and the newer ОІ-lactam antibiotics (80, 107, 130, 131, 132). The epidemiologies and clinical presentations of these two species are similar. Enterobacter Species There are now 11 named species of Enterobacter, including microorganisms previously allocated to the genera Aerobacter and Erwinia. The most frequent species isolated from clinical material is Enterobacter cloacae, which is much more common than the next most frequent species, Enterobacter aerogenes (34, 36). In the United States, Enterobacter species have replaced Klebsiella species as the third most common cause of gram-negative nosocomial infection after E. coli and P. aeruginosa (47, 94, 133). This is probably due to the selection of resistant mutants by the increasing clinical use of cephalosporins. Enterobacter species are inherently resistant to first-generation cephalosporins and can develop chromosomally mediated resistance to second- and third-generation cephalosporins (133, 134, 135), sometimes during the treatment of individual patients (136). Enterobacter species possess an inducible chromosomally encoded class I ОІ-lactamase that is normally suppressed by a repressor gene and is produced in large amounts only after exposure to certain ОІ-lactams. Full resistance to second- and third-generation cephalosporins results when stably derepressed mutants appear that express the class I ОІ-lactamase constitutively. These mutants are selected by cephalosporin therapy and produce the ОІ-lactamase continuously. Enterobacter species have a similar ability to that of Klebsiella species to survive on skin and dry surfaces (89), but Enterobacter species are more able to survive in nutritionally poor fluids such as 5% dextrose and have often caused outbreaks associated with contaminated intravenous solutions (32, 33, 34). Although Enterobacter species are well recognized as nosocomial pathogens, they appear to cause hospital outbreaks less frequently than Klebsiella species or Serratia species. Several studies have shown that the emergence of multiresistant Enterobacter species is related to use of second- and third-generation cephalosporins, especially as prophylaxis (61, 133). Serratia Species These are small aerobic gram-negative bacilli whose normal habitat is soil and water, but they are sometimes found as mucosal commensals of humans. There are several species, of which the most common in clinical material is Serratia marcescens followed by Serratia liquefaciens, previously known as Enterobacter liquefaciens. They are inherently resistant to cephalosporins and polymyxins and readily acquire resistance factors to ampicillin and aminoglycosides, but they are usually susceptible to cotrimoxazole (137). Multiresistant Serratia species have become more common, but the degree of resistance varies in different areas (137, 138, 139, 140). They produce typical opportunistic infections, having a similar epidemiology and clinical presentation to Klebsiella and Enterobacter species, although Serratia species are the least common of the three. Most clinical isolates represent colonizations, but bacteremia sometimes occurs. Pseudomonas and Pseudomonas-Like Species These are nonfermenting, aerobic, gram-negative bacteria that are widely distributed in nature, are nonfastidious in their nutritional requirements, and can survive and multiply in many wet environmental sites, often at ambient or low temperatures. They also readily colonize mucous membranes of compromised P.1619 patients who have been treated with multiple courses of antibiotics. Although they have little pathogenicity for normal individuals, they are resistant to many common antimicrobials and disinfectants and flourish as environmental opportunistic pathogens in intensive care and similar units. Since these microorganisms survive in many types of liquid media, they are sometimes the cause of “pseudobacteremia”; that is, they may be isolated from blood culture bottles following ward or laboratory contamination rather than patient infection (141). Colonized patients may later go on to develop invasive disease, but the mere isolation of a pseudomonad from a clinical specimen does not necessarily indicate infection, and individual patients should be assessed clinically before treatment decisions are made. Although many species of Pseudomonas and Pseudomonas-like microorganisms have been isolated from clinical material, the ones that cause most problems of antibiotic-resistant nosocomial infection are P. aeruginosa, Stenotrophomonas (formerly Xanthomonas or Pseudomonas) maltophilia, Burkholderia (formerly Pseudomonas) cepacia, and Ralstonia (formerly Pseudomonas or Burkholderia) pickettii. Achromobacter xylosoxidans is a nonfermenting gram-negative bacillus that behaves like Pseudomonas and causes similar hospital infections. Pseudomonas aeruginosa This is the most common pseudomonad isolated from clinical specimens and the most frequent species causing invasive infection. It accounts for about 10% of all hospital-acquired infection and is about the third most common cause of hospital-acquired gram-negative bacteremia after E. coli and K. pneumoniae (71). It is a normal commensal of humans, colonizing skin, nose, throat, and stool in a widely varying number (0–40%) of healthy subjects (97). Hospitalized patients have a higher rate of colonization of these sites, which increases with length of stay (59, 61, 142). Colonization is encouraged by the use of broad-spectrum antibiotics to which P. aeruginosa is resistant, and invasive infection may follow in the compromised host. P. aeruginosa septicemia is associated with high mortality rates. P. aeruginosa can be typed by a variety of methods including several molecular methods (143). Many studies have shown that several different types may be in circulation during an apparent outbreak, and while person-to-person spread does occur, endogenous infection is common (144, 145, 146). Carriage of clinically undetectable resistant P. aeruginosa may be common in normal persons, and this resistant population may emerge under antibiotic pressure in hospitals to cause environmental colonization and endogenous infection (145, 146). P. aeruginosa tolerates a wide range of temperatures and is often found in wet hospital environmental sites such as sinks, disinfectants, humidifier water of ventilators and incubators, water baths, and suction apparatus (65). It is also a common contaminant of medicinal jellies and ointments. P. aeruginosa can multiply in these environmental sites and then gain access to compromised patients, leading to colonization of oropharyngeal and respiratory mucosa, bladder, wounds, skin, and bowel. It should be noted, however, that environmental sites can just as well be contaminated by patients as the reverse, and although sinks often contain multiply resistant pseudomonads, they are not often the source of patient infection (27, 142). P. aeruginosa is inherently resistant to most penicillins and cephalosporins, tetracyclines, chloramphenicol, sulfonamides, and nalidixic acid. It is naturally susceptible to the aminoglycosides, antipseudomonal penicillins and cephalosporins, quinolones, and carbapenems. However, acquired antibiotic resistance in P. aeruginosa is common. The microorganism can exchange antibiotic resistance plasmids with other gram-negative bacilli while colonizing patients (147, 148), but acquired resistance to aminoglycosides and other agents is probably more often the result of changes in membrane permeability (149, 150). Resistance to fluoroquinolones (due to mutations in DNA gyrase, membrane permeability, or both) has emerged relatively rapidly in P. aeruginosa and now about a third of hospital isolates are resistant (151) (Table 91.1). This microorganism can develop resistance to ceftazidime by mutation to constitutive production of chromosomal class I ОІ-lactamase (134, 135), and this may occur during treatment (152). It may also, though less readily, develop resistance to carbapenems such as imipenem and meropenem, usually by changes in membrane permeability (47, 153, 154). In the NNIS studies between 1994–1998 and 1999, resistance to quinolones and carbapenems in ICU isolates of P. aeruginosa increased by 49% and 35%, respectively (Table 91.2). Bacteremia is often a terminal event in highly immunocompromised patients dying from underlying disease, and it is the major cause of death in burn patients in some centers, in whom P. aeruginosa bacteremia has a mortality rate of more than 70% (155). Neutropenic and burn patients should be treated with a synergistic combination of an antipseudomonal ОІ-lactam, such as ceftazidime, with an aminoglycoside (156, 157, 158). Stenotrophomonas maltophilia Stenotrophomonas maltophilia (formerly Xanthomonas or Pseudomonas maltophilia) is a free-living, opportunistic, gram-negative nonfermenter, less frequently isolated than P. aeruginosa but similar in its epidemiology and clinical presentation (159, 160, 161). However, S. maltophilia is more antibiotic-resistant, often showing resistance to all aminoglycosides and to carbapenems, although it is characteristically susceptible to cotrimoxazole and tetracyclines. Its ability to develop multiple acquired resistance is partly related to outer membrane impermeability and the production of inducible broad-spectrum ОІ-lactamases (162). Because of these inherent and acquired multiple resistances, S. maltophilia is being seen with increasing frequency as an opportunistic pathogen in immunocompromised patients in intensive care and other high-dependency units, especially in areas of heavy imipenem use (94). S. maltophilia infections have been treated successfully with combinations of cotrimoxazole, antipseudomonal penicillins and cephalosporins, and tetracyclines, but sensitivities need to be confirmed at the start of therapy and monitored during treatment. Burkholderia cepacia Burkholderia cepacia (formerly known as Pseudomonas cepacia or Pseudomonas multivorans) is a cause of endemic and epidemic hospital-acquired infection, usually associated with contamination of wet hospital environments, especially disinfectants (163, 134, 165) and intensive care equipment (35, 166). This microorganism can colonize mucous membranes and, like other pseudomonads, P.1620 occasionally produces invasive infection in immunocompromised patients, but B. cepacia appears to be even less pathogenic than P. aeruginosa, and the differentiation between colonization and infection is often difficult. B. cepacia is characteristically resistant to aminoglycosides and most ОІ-lactam antibiotics, but it is normally susceptible to cotrimoxazole and chloramphenicol. However, additional acquired multiple resistance is becoming more common (167), and the choice of therapy for true B. cepacia infection should be guided by the results of sensitivity tests. Multiply resistant B. cepacia causing colonization and severe lung infections has been seen in cystic fibrosis patients, sometimes associated with a high mortality rate (168, 169). In these patients, cross-infection may sometimes occur in both the community and the hospital (166, 170). Ralstonia pickettii This microorganism was previously known as Pseudomonas pickettii or Pseudomonas thomasii, but later transferred to the genus Burkholderia (171) and then Ralstonia (172). It is of low virulence and a relatively uncommon cause of human and hospital infection, but may be associated with outbreaks caused by contamination of supposedly sterile fluids for injection or infusion (173). Like other such opportunists, the microorganism may cause pseudobacteremias or multistrain outbreaks. It is of low virulence, usually causing mucosal colonizations and sometimes bacteremias and other more serious infections. Isolates are usually resistant to aminoglycosides, ampicillin, and colistin but susceptible to chloramphenicol and newer cephalosporins. Achromobacter xylosoxidans The taxonomic position of this microorganism is confused. DNA homology studies suggest that it and Alcaligenes denitrificans should be classified together as two subspecies of Alcaligenes xylosoxidans (174). A. xylosoxidans subspecies xylosoxidans (Achromobacter xylosoxidans) is very disinfectant-resistant and can survive in cetrimide (like P. aeruginosa) and in 1% chlorhexidine for 10 minutes or more (175). Not surprisingly, therefore, it has caused a number of hospital outbreaks associated with contaminated disinfectants and other wet sites (174, 176). It is characteristically susceptible to cotrimoxazole, ceftazidime, and fluoroquinolones but resistant to aminoglycosides. It resembles P. aeruginosa in its epidemiology but appears to be rather less pathogenic. Although some reports suggest that this microorganism is being isolated with increasing frequency (176), in the 20-year study of more than 4,000 episodes of septicemia at St. Thomas's Hospital in London, there were only two episodes of Achromobacter septicemia and one of Alcaligenes (71). Acinetobacter baumannii Acinetobacter species are nonfermenting gram-negative coccobacilli found widely distributed as free-living saprophytes in soil and water. They also colonize the skin and mucous membranes in about 25% of normal people (177, 178). The classification and nomenclature of this group have undergone frequent changes, and until recently only one species was recognized with various biochemical variants. The most frequently isolated Acinetobacter, the one most likely to acquire multiple antibiotic resistance, and the commonest cause of hospital outbreaks, is Acinetobacter baumannii (179), formerly known as Acinetobacter calcoaceticus var. anitratus and in the past allocated to other genera such as Mima, Herellea, Achromobacter, and Moraxella. Hospital outbreaks originate from contaminated environmental sources or follow hand transmission from the skin of colonized patients (180, 181). These microorganisms can also survive for long periods on dry surfaces (182, 183, 184) and can probably be transmitted via dust and fomites (185, 186, 187). Most clinical isolates represent colonization rather than infection (181), but serious and sometimes fatal infections occur in compromised patients, including septicemia, endocarditis, meningitis, and pneumonia (178, 188). In the early 1970s, Acinetobacter species were usually susceptible to many common antimicrobials, including gentamicin and the cephalosporins, and they were relatively uncommon hospital pathogens (189). By the mid-1980s, however, hospital outbreaks with multiply resistant Acinetobacter strains were being frequently reported (178, 190) and were dubbed “bacteria resistant to everything” (191). Many hospital strains are now resistant to the aminoglycosides and to older and newer cephalosporins, and some have developed resistance to the quinolones (192, 193) and carbapenems (194). A. baumannii is usually susceptible in vitro to ОІ-lactamase inhibitors such as clavulanic acid and, thus, to co-amoxiclav (amoxicillin plus cluvulanic acid), ampicillin plus sulbactam, and piperacillin plus tazobactam, but these agents may not be effective clinically. The mechanisms and genetics of resistance in this species are complex and difficult to investigate (195), but they involve several plasmid-borne ОІ-lactamases and aminoglycoside-modifying enzymes as well as alterations in membrane permeability and penicillin-binding proteins (PBPs) (189, 194, 195, 197). The ability of A. baumannii to acquire multiple resistances, as well as to survive on skin and in the environment, undoubtedly contributes to its success as a nosocomial pathogen. Gram-Positive Bacteria Staphylococcus aureus Staphylococcus aureus is usually the second most common bacterial isolate in hospital laboratories after E. coli and is associated with wound infections and septicemia (71). Surface isolates often represent colonization, but invasive infection causes high morbidity and may be fatal. S. aureus is naturally susceptible to many classes of antimicrobials, including penicillins, cephalosporins, macrolides, sulfonamides, trimethoprim, tetracyclines, chloramphenicol, lincosamines, aminoglycosides, quinolones, and glycopeptides, but it has great ability to develop resistance to many of these drugs simultaneously. Antibiotic resistance facilitates the survival and spread of these microorganisms in the hospital environment, and multiresistant strains are often responsible for large and serious outbreaks of nosocomial infection. Since the 1950s, many different resistance problems have been encountered (66, 67). Penicillin resistance due to the production of plasmid-mediated penicillinase appeared in S. aureus soon after penicillin was introduced (198) and increased to 85% by the late 1970s (199). During the 1950s, multiresistant strains of S. aureus began to appear, and large epidemics of hospital infection P.1621 with microorganisms resistant to penicillin, tetracycline, erythromycin, chloramphenicol, and other drugs were seen throughout the world. Many of these outbreaks were caused by virulent microorganisms of phage type 80/81, a group that became known as “the hospital staphylococcus” (200, 201, 202, 203). The hospital staphylococcus was greatly feared, because infections were often untreatable and outbreaks were associated with high mortality rates. Gentamicin resistance was uncommon in the 1960s, but some hospitals experienced outbreaks with gentamicin-resistant S. aureus in the 1970s (204), and during this time gentamicin resistance was used as a marker of potentially epidemic strains. In general, however, the incidence of hospital infection with multiply resistant staphylococci gradually declined during the 1960s and 1970s (42, 199, 205, 204, 205, 206, 207). The exact reasons for this are unclear, but the decline was associated with the introduction in the 1960s of the penicillinase-stable semisynthetic penicillins, methicillin, nafcillin, oxacillin, and cloxacillin (which are active against penicillinase-producing staphylococci), an apparent loss of virulence in the phage type 80/81 strains, and improvements in hospital infection control (66, 67). Strains of MRSA were noted soon after methicillin was introduced into clinical practice (208), but they were generally rare until the 1980s despite widespread use of methicillin, cloxacillin, and related drugs (42). In the late 1970s, however, MRSA emerged as a major pathogen of hospital infection in most countries and regions of the world (209). In both the U.S. and Europe, around 30% to 50% of hospital isolates of S. aureus are now methicillin resistant (87, 151) (Table 91.1), although in the Netherlands and Scandinavia rates are less than 1% (87). In a given population of MRSA, not all daughter cells may express methicillin resistance. This is called “heterogeneous resistance,” and commonly, under routine culture conditions, less than 1% of cells may be phenotypically resistant (210, 211). To improve detection during in-vitro susceptibility testing, special conditions are required to increase the proportion of cells expressing methicillin resistance. These include reducing the incubation temperature to 30В or 35ВC, prolonging the incubation time to 48 hours, and making the culture medium more hypertonic—for example, by increasing the NaCl content to 5% (212, 213). If these special test conditions are not used, laboratories may fail to identify some methicillin-resistant strains. Methicillin resistance is mediated primarily by the production of an abnormal PBP called PBP-2a or PBP-2′ (214, 215, 216). ОІ-Lactam antibiotics bind to normal bacterial PBPs and inhibit their activity, preventing proper formation of cell wall peptidoglycan and leading to cell death by osmotic lysis. PBP-2a binds poorly with most ОІ-lactams and can fulfill the functions of the so-called essential PBPs 1, 2, and 3 (217). Microorganisms producing PBP-2a are thus resistant to most available ОІ-lactams, including methicillin and the isoxazolyl penicillins. Although they may appear susceptible to some ОІ-lactams in vitro, the agents so far tested are clinically ineffective and should not be used for therapy. The production of PBP-2a is encoded by the mecA gene located on the chromosome. This gene appears to have been derived from coagulase-negative staphylococci, hospital strains of which are now frequently methicillin-resistant (218). Recent genetic studies suggest that MRSA has repeatedly emerged from methicillin-sensitive S. aureus (MSSA) at different times in different parts of the world (219, 220). MRSA strains are resistant to methicillin, oxacillin, and other penicillinase-stable ОІ-lactams including the carbapenems, and to several other classes of antibiotic. Following the rapid emergence of resistance to quinolones (221, 222, 223, 224), many strains of MRSA remain susceptible only to the glycopeptides vancomycin and teicoplanin, and vancomycin is the drug of choice for serious infection (225, 226). There are a number of new drugs under development for the treatment of multiresistant gram-positive bacteria, including new glycopeptides, quinolones, ketolides, oxazolidinones, and the streptogramin combination quinupristin/dalfopristin, but the role of these agents in the treatment of MRSA remains to be elucidated (217, 226). Because of the present importance of vancomycin and teicoplanin in the treatment of severe MRSA sepsis, the emergence of P.1622 glycopeptide resistance in MRSA is greatly feared. Unfortunately, several types of glycopeptide resistance have emerged in MRSA in recent years. The glycopeptides are normally slowly bactericidal for S. aureus. However, some recent isolates of MRSA exhibit glycopeptide tolerance, that is, they are inhibited by normal concentrations of these agents but are not killed (227, 228). Tolerance has been associated with treatment failures, but its exact clinical significance is unclear. Glycopeptide tolerance is not routinely tested, and tolerant strains usually go undetected. There have been some reports of S. aureus strains with reduced vancomycin susceptibility from Japan, North America, and Europe (229, 230, 231). These strains have non–plasmid-mediated low-level or “intermediate” resistance to vancomycin, with vancomycin minimum inhibitory concentration (MIC) of 8 Вg/mL, and have been associated with treatment failures. They have been designated “vancomycin-intermediate S. aureus” (VISA). In Japan, some strains showing “heterogeneous” vancomycin resistance have affected many hospitals (232). In a given population of these strains, the majority have vancomycin MICs of 2 to 4 Вg/mL, but there is a subpopulation with MICs of 5 to 9 Вg/mL that may emerge under glycopeptide pressure. The mechanism of vancomycin resistance in these microorganisms has not been fully elucidated but may result from increased amounts of normal D-Ala–D-Ala residues in the cell wall that absorb therapeutic concentrations of vancomycin (233). These VISA strains appear to be rare and their true clinical significance is uncertain. As with glycopeptide tolerance, GISA strains are not routinely identified in the laboratory but may be identified retrospectively after treatment failure (234). High-level, inducible, transferable resistance to both vancomycin and teicoplanin is now seen quite commonly in enterococci, and is encoded by a series of genes, including vanA (see below). This vanA resistance is usually plasmid-borne and was transferred to S. aureus in the laboratory in 1992 (235). Ten years later, two clinical isolates of MRSA that contained the vanA gene and had vancomycin MICs of >128Вg/mL and teicoplanin MICs of 32 Вg/mL, were reported from the U.S. (236, 237). Such strains are still exceptionally rare, but since both MRSA and vancomycin-resistant enterococci (VRE) are widespread in hospitals throughout the world, there is fear that fully glycopeptide-resistant MRSA will become common nosocomial pathogens in the near future. It is essential to avoid any unnecessary use of glycopeptides that might encourage the emergence of such strains, to maintain vigilant surveillance for their appearance, and to strictly isolate any cases that do occur to prevent further spread. There has been debate over the clinical significance of MRSA, some holding that these microorganisms are merely opportunistic commensals of low pathogenicity that colonize highly compromised patients but contribute little to morbidity or mortality (238). Nevertheless, MRSA strains appear similar to methicillin-sensitive strains in their abilities to produce invasive infection in humans and animals (225, 239) and to cause deep infections such as septicemia, osteomyelitis, severe pneumonia, and brain abscesses. Mortality rates in MRSA septicemia are high, partly due to the poor prognosis of the underlying diseases seen in these patients but also to the failure of standard antimicrobial therapy against these microorganisms. Most authors with experience in MRSA outbreaks would agree with Waldvogel (240) that “data clearly define MRSA as a major pathogen, fully equipped to produce infections and death,” and conclude with Casewell (241) that “the clinical importance of MRSA is now indisputable.” MRSA strains are primarily hospital pathogens and are usually seen in tertiary referral centers. However, MRSA also readily colonize elderly patients in nursing homes (242, 243, 244). These institutions may act as reservoirs of MRSA, continually reseeding acute care hospitals with resistant staphylococci carried by patient transfers. Some MRSA strains have particular abilities to spread in hospitals (and sometimes into the community) and have been called “epidemic methicillin-resistant S. aureus” (EMRSA) strains to distinguish them from other MRSA strains (245, 246). Within hospitals, the sources of cross-infection with MRSA are usually infected or asymptomatic patients who may be colonized in the nose, pharynx, rectum, wounds, and chronic skin lesions. Nasal carriage by staff members is usually low, on the order of 1% to 8%, but staff members may transfer MRSA between patients by hand contact, either directly from patient to patient or via fomites (247, 248). Although MRSA may be spread by airborne transmission, this appears to be less common than with methicillin-sensitive strains. The risk of colonization and infection with MRSA increases with length of hospitalization, severity of underlying disease, number of operations or manipulations, and previous exposure to antibiotics, especially cephalosporins and aminoglycosides (249, 250). Although some types of MRSA appear sporadically and rarely cause outbreaks, epidemic strains spread rapidly in hospitals and may become endemic. Once established within a hospital, MRSA may be very difficult to eradicate (251). Nevertheless, most authorities believe that vigorous efforts should be made to control outbreaks of MRSA, especially if infection is not yet endemic. A U.K. working party of the British Society for Antimicrobial Chemotherapy, the Hospital Infection Society, and the Infection Control Nurses Association has published detailed guidelines for the control of epidemic and endemic MRSA (252). Briefly, infected patients should be isolated; others on the ward should be screened for carriage, and colonized patients should be isolated in cohorts or discharged home; infected patients should be treated systemically, if necessary, with glycopeptides; nasal carriage should be cleared by topical agents, and skin carriage by disinfectant baths; if the outbreak is not brought quickly under control, staff members should be screened and carriers removed from critical areas until they have been cleared. Cohorting of new cases as they appear and strict attention to hand washing are of the utmost importance. The control of moderately sized or large outbreaks may require the closure and cleaning of affected wards; control may be facilitated by having a dedicated infection isolation ward (253). Despite such control policies, many hospitals are now affected by endemic MRSA. Eradication is difficult, because colonized patients are often readmitted after discharge and in tertiary referral centers colonized patients are constantly being admitted from other institutions. Under these circumstances many authorities believe that attempts to control all MRSA colonizations is not cost-effective, and instead efforts should be directed toward control in high-risk wards such as orthopedics, cardiothoracic surgery, and intensive care (252). Topical mupirocin is widely used for the clearance of nasal carriers of MRSA during outbreaks (247, 254, 255). Susceptible strains have MICs of less than 1 Вg/mL, and the ointment contains 20,000 Вg/mL. Resistance to mupirocin is uncommon, but rates tend to be higher in patients given prolonged treatment such as those in dermatology clinics and during outbreaks of mupirocin-resistant strains. Mupirocin acts by inhibiting bacterial isoleucyl–transfer RNA (tRNA) synthetase, and resistance appears to be mediated by the production of modified enzymes. Isolates showing low-level resistance have a single chromosomally encoded modified synthetase, whereas those with high-level resistance also have a second enzyme encoded on a plasmid (256, 257, 258). Staphylococci can be trained to low levels of mupirocin resistance (MICs <64 Вgm/L in vitro, and similar low-level resistance may emerge during therapy. The clinical significance of such resistance is uncertain, since topical mupirocin concentrations are very much higher than these MICs, and carriage of low-level resistant strains can be eradicated with normal mupirocin therapy (254). More important are isolates showing high-level resistance (MICs >1,024 Вg/mL), which cannot be cleared by mupirocin therapy (259). This type of resistance may be carried on a conjugative plasmid or transposon and can transfer to other microorganisms (260). Since mupirocin is so useful in the management of S. aureus outbreaks, the use of this agent should be carefully controlled to preserve its effectiveness. MRSA strains are usually brought into hospitals by asymptomatic carriers, either patients or staff members. An important control measure is to screen patients admitted from other hospitals and keep them in isolation until they are shown not to be carriers. Similarly, new staff members who have recently worked at other hospitals (including agency staff members) should not be allowed to work until they have been shown to be free of MRSA. It is also good practice to inform other hospitals if infected or colonized patients are to be transferred to them. Coagulase-Negative Staphylococci There are many species of coagulase-negative staphylococci, of which the commonest isolated from clinical material is S. epidermidis. P.1623 At one time, coagulase-negative staphylococci were regarded as insignificant pathogens of humans, but they are now recognized as increasingly important causes of infection in hospitalized and compromised patients. Many of these microorganisms are multiply antibiotic-resistant (78, 261, 262, 263) and can produce an extracellular “slime” that allows them to stick to plastic prostheses and survive on foreign surfaces within a protective biofilm (72, 73, 74, 264). As a result, infections with coagulase-negative staphylococci are being seen with increasing frequency in compromised patients. These include bacteremia (associated with intravascular catheters and vascular grafts), endocarditis (prosthetic heart valves), meningitis (ventricular shunts), peritonitis (peritoneal dialysis catheters), and infection of joint prostheses. Coagulase-negative staphylococci are now common isolates from blood cultures (71), usually associated with vascular lines, especially indwelling and long-term ones such as Hickman lines (72, 264, 265). About half the strains isolated in hospitals show multiple antibiotic resistance, including resistance to methicillin (and P.1624 other ОІ-lactams) and gentamicin. Methicillin-resistant strains tend to be more multiply resistant than methicillin-sensitive ones. Healthy individuals are normally colonized by relatively sensitive microorganisms, primarily S. epidermidis. After admission to the hospital, and especially after exposure to multiple courses of antibiotics or surgical prophylaxis, patients become colonized with multiply resistant strains and with other more resistant coagulase-negative species such as Staphylococcus hemolyticus (266, 267, 268). Resistance in coagulase-negative staphylococci appears to be increasing, probably under pressure of antibiotic use (269, 270). Sensitive staphylococci may receive plasmid-borne resistance factors from other microorganisms during contact on the skin surface, and there is evidence that coagulase-negative staphylococci may be a reservoir of resistance genes that can be transferred to S. aureus (271, 272). Because of extensive multiple resistance in coagulase-negative staphylococci, the glycopeptides vancomycin and teicoplanin are often used for therapy and prophylaxis in high-risk patients. Low-level resistance to glycopeptides has appeared in hospital isolates of coagulase-negative staphylococci, and such resistance can be produced by exposure to increasing drug concentrations in vitro. Teicoplanin resistance is easier to produce than vancomycin resistance, and MICs are higher (273). Similar low-level teicoplanin-resistant, vancomycin-sensitive strains are being increasingly isolated from clinical specimens (274, 275, 276). There is some evidence that S. hemolyticus is more likely to exhibit teicoplanin resistance than are other coagulase-negative species, but not all studies have shown this. Glycopeptide resistance is probably related to the increasing use of these drugs, and the emergence of resistant strains following intraperitoneal vancomycin treatment of chronic ambulatory peritoneal dialysis (CAPD) peritonitis has been reported (277). Epidemiologic investigations were previously hampered by the lack of good typing systems, but new molecular methods have revealed clusters of hospital infection with indistinguishable strains of coagulase-negative staphylococci (278, 279, 280, 281). In most instances, however, the sources and routes of transmission of the outbreak strains are unclear. In general, therefore, infection with coagulase-negative staphylococci should be regarded as endogenous unless clustering of unusually resistant isolates is noted. Colonization and infection with resistant strains are more likely with prolonged hospitalization and multiple courses of antibiotic therapy, and these should be avoided when possible. Eradication of infection usually requires the removal of the colonized catheter or prosthesis. Multiply Resistant Coryneform Bacteria Johnson and Kaye (282) were the first to describe clinical isolates of multiply antibiotic-resistant coryneforms that became known as the JK group of corynebacteria and were later distinguished by the species name Corynebacterium jeikeium (283). These microorganisms are inherently resistant to many common antibiotics, hospital isolates often being sensitive only to vancomycin (284, 283, 284, 285, 286). They are found on the skin of healthy individuals, more often in men and postmenopausal women, in whom the fatty acid composition of epidermal fats may favor the survival of these microorganisms. Hospitalized patients tend to become colonized with multiply resistant strains, especially after multiple courses of antibiotic treatment, and may remain carriers for weeks or months. Staff members in high-risk units such as oncology departments may also become colonized with multiply resistant coryneforms (287). These microorganisms are classic opportunistic pathogens, having low virulence for healthy individuals, but causing local skin sepsis and bacteremia in the compromised, especially those with hematologic and other malignancies. They may also cause bacteremia and endocarditis in association with vascular catheterization and prosthetic implants such as heart valves (288, 289). Thus, in many respects, C. jeikeium behaves clinically like multiply resistant coagulase-negative staphylococci, producing primarily endogenous infection in highly compromised patients after prolonged hospitalization, often in association with vascular and prosthetic foreign bodies. The prevention of such resistant infections is also similar: the likelihood of colonization can be reduced by avoiding unnecessary antibiotic use, and the theoretic possibility of spread to others can be limited by isolating colonized patients and emphasizing hand washing by staff members. Enterococci Enterococci are found in the stools of most normal people and sometimes in other sites such as the mouth and vagina. Enterococcus faecalis and Enterococcus faecium predominate, with E. faecalis usually being the most common. Other enterococcal species are infrequent human commensals. The enterococci typically cause endogenous infections, most commonly of the urinary tract, but also of the abdomen and pelvis, where they are usually mixed with other bowel flora. They are relatively poor pathogens but may go on to cause invasive disease in compromised patients, causing cholangitis, septicemia, endocarditis, and meningitis (290). Multiresistant strains of enterococci cause hospital outbreaks in which they colonize the bowels of asymptomatic patients and are transferred between patients on staff members' hands (290, 291). The enterococci are typically susceptible to ampicillin/amoxicillin but intrinsically relatively resistant to benzylpenicillin and other ОІ-lactams such as cloxacillin, the cephalosporins, and the carbapenems. They are also usually resistant to trimethoprim and the sulfonamides, the quinolones, low levels of aminoglycosides, and low levels of clindamycin. Furthermore, these microorganisms have a remarkable ability to acquire new resistances to ampicillin/amoxicillin and other drugs that might be used against gram-positive bacteria, including chloramphenicol, erythromycin, tetracycline, high levels of aminoglycosides and clindamycin, and now the glycopeptides vancomycin and teicoplanin. E. faecium is inherently more resistant to penicillin and ampicillin than E. faecalis, and hospital isolates have tended to show increasing high-level resistance (292). This high-level ampicillin resistance is probably due to changes in affinity of the enterococcal PBPs and contributes to the growing importance of E. faecium as a nosocomial pathogen. Transferable ОІ-lactamase–mediated ampicillin resistance has been reported in E. faecalis, and although such strains have caused several large hospital outbreaks (293, 294), they are usually rare in clinical material. Because the enterococci are intrinsically resistant to the most commonly used antimicrobials, they have become increasingly important as causes of infection and superinfection in hospitalized patients (75, 295). Nosocomial enterococcal infections are increasing in prevalence and now cause 10% to 12% of all hospital-acquired infection, 10% to 20% of hospital-acquired urinary tract infections, and 5% to 10% of hospital-acquired bacteremias (76, 296). Most hospital infections are endogenous, arising from the patient's own bowel, but outbreaks of cross-infection via staff hands or by environmental contamination does occur (297, 298, 299, 300, 301). Because of their great ability to acquire multiple resistances, the enterococci are one of the few bacterial groups that can become resistant to all available antibiotics. Many of these resistances are borne on transferable plasmids, and it has been demonstrated in vitro that the enterococci have the potential to transfer them to streptococci and staphylococci as well as to other enterococci. For these reasons, the enterococci have fulfilled the prediction that they were set to become the most important and problematic nosocomial pathogens of the 1990s (302). Glycopeptide-Resistant Enterococci The glycopeptides inhibit synthesis of gram-positive cell walls by binding to the amide bond of the D-alanyl–D-alanine terminal sequences of the muramyl pentapeptide of the elongating peptidoglycan polymer. The large glycopeptide molecules then impede the action of both the polymerase that extends the peptidoglycan backbone and the transpeptidase that cross-links the growing chain to the existing cell wall (303, 304). Most clinically important gram-positive bacteria are naturally susceptible to the glycopeptides vancomycin and teicoplanin. Vancomycin resistance can be divided into low-level (MICs of 8–32 Вg/mL) and high-level (MICs ≥64 Вg/mL). Acquired glycopeptide resistance is rare but is most frequently seen in enterococci, which exhibit at least four resistance phenotypes (303, 305): (a) vanA, high-level transferable resistance to both vancomycin and teicoplanin, associated with the production of a 38- to 40-kd membrane protein; (b) vanB, inducible low-level resistance to vancomycin alone that, in some strains, is associated with a 39.5-kd membrane protein; (c) vanC, constitutive low-level vancomycin resistance seen in some strains of Enterococcus gallinarum; and (d) vanD, described in only a few strains of E. faecium, with constitutive resistance to vancomycin (MICs ~64 Вg/mL) and to low levels of teicoplanin (MICs ~4 Вg/mL). Enterococcus casseliflavus/Enterococcus flavescens appear to have intrinsic low-level resistance unrelated to that of the other phenotypes. As more glycopeptide-resistant strains are investigated, an increasingly wider range of resistant phenotypes are being described, some resulting from alterations or deletions of the genes encoding the more common types. Low-level resistance usually involves only one of the glycopeptides and is encoded on the chromosome. The vanA phenotype of high-level resistance to both vancomycin and teicoplanin is usually encoded on a transferable plasmid and is a potentially more serious clinical problem. vanA strains have vancomycin MICs of 64 to more than 1,024 Вg/mL and teicoplanin MICs usually one or two times lower than this. This phenotype has been seen so far only in clinical isolates of enterococci, most frequently in E. faecium, sometimes in E. faecalis, and rarely in Enterococcus avium. The vanA gene encodes an abnormal D-Ala–D-Ala ligase, which results in the replacement of the normal D-Ala–D-Ala termini of peptidoglycan precursors by D-Ala–D-lactate, which cannot bind glycopeptides (305, 306, 307, 308, 309). The successful production of the vanA glycopeptide resistance phenotype is dependent on the cooperative activity of the products of seven genes, which in E. faecium BM4147 are contained in a transposon Tn1546 (307) that is usually encoded on a plasmid but sometimes transfers to the chromosome. The mechanisms and genetics of the other vancomycin resistance phenotypes have not been so well elucidated, but they all seem to result from the production of altered ligases. The vanB phenotype is encoded by a similar gene cluster encoded on a transposon Tn1547 and containing the vanB gene (310, 311, 312). The gene product vanB encodes a ligase that has a 76% amino-acid identity with vanA and is presumably responsible for the formation of D-Ala–D-Lac (313). Enterococci expressing vanB are resistant to vancomycin but remain susceptible to teicoplanin, presumably because teicoplanin does not induce resistance. vanC in E. gallinarum encodes a ligase that substitutes D-Ala–D-Ser for the normal D-Ala–D-Ala in peptidoglycan precursors. The vanD gene encodes a D-Ala–D-Lac ligase related to vanA and vanB (314, 315). The vanA gene is variably transferable by conjugation or transformation in vitro to other gram-positive bacteria, including S. aureus (235), but it has not, until recently, been passed to other genera naturally. However, as described above, there were reports from the U.S. in 2002 of two unrelated clinical isolates of MRSA that had acquired the vanA gene, presumably from enterococci, and expressed high-level vancomycin and teicoplanin resistance (236). Continuing surveillance will reveal whether such strains will increase in prevalence in the future. Vancomycin has been used for several decades, but acquired resistance was rare until a multiple strain outbreak of vancomycin and teicoplanin resistant enterococci appeared in London in 1986 (316). Since then, such strains have been seen throughout P.1625 the world. They are common in the U.S., where the NNIS system survey found a 20-fold increase in nosocomial VRE isolates during the period 1989–1993 (317), and a 47% increase in ICU isolates between 1994–1998 and 1999 (13). In U.S. ICUs, about 12% of hospital isolates of enterococci are VRE. They are much less common in Europe, where only about 1% of blood isolates of E. faecalis (range in different countries 0–7%) and 5% of E. faecium (range 0–21%) are resistant (87). Twelve of the 20 European countries surveyed by EARSS reported no VRE from the blood. The reservoir of enterococci is the colonized bowel of patients, and most infections are endogenous. Thus the increasing isolation of enterococci is usually caused by the multiple endogenous strains rather than outbreaks of cross-infection. Nevertheless, epidemic infection does occur, and microorganisms probably spread from patient to patient on staff hands (297, 298, 299, 300). During outbreaks of both vancomycin-sensitive enterococci (VSE) and VRE, there is extensive colonization of patient and staff bowel and asymptomatic carriage may persist for months (301, 318, 319). Colonization of other mucous membranes such as throat, stomach, and vagina, and skin colonization of moist sites such as groins may occur. Microorganisms may then be transferred from these sites by hand contact. Evidence for this is provided by the isolation of outbreak strains of VRE and VSE from environmental surfaces likely to have had hand contact such as telephones, stethoscopes, instrument dials, and doorknobs. Boyce et al. (301) found that during an outbreak of enterococci carrying transferable VanB resistance, there was extensive contamination of the environment, which was significantly more widespread around colonized patients who also had diarrhea. After experimental inoculation VSE and VRE survive on fingers for about 30 minutes. Washing with soap and water fails to remove these microorganisms. Aqueous chlorhexidine and povidone iodine are also unreliable but alcohol and alcoholic chlorhexidine are effective (320, 321). Large hospital outbreaks with VRE have a number of similarities. Patients are usually on renal, pediatric, oncologic, intensive care, or other special units in which glycopeptides are used. Although cross-infection does occur, multiple enterococcal strains are often involved, usually of more than one species, and outbreaks often appear to be caused by multiple microorganisms that have acquired resistance via transposons. Asymptomatic stool carriage is common, often lasting weeks or months, and may contribute to the spread of resistant strains into the community. Although most isolates represent colonization or minor infection, septicemia and other serious invasive infection does occur and may be associated with fatalities. Outbreaks should be dealt with by isolation and hand washing; antibiotic pressure should be reduced by restricting the use of glycopeptides, and methods should be sought to eliminate stool carriage of resistant microorganisms. Although the origin of the vancomycin-resistance transposons is obscure, the emergence of this resistance has occurred during a time when the glycopeptides have been increasingly used for the treatment of multiresistant staphylococci, enterococci, and Clostridium difficile–associated diarrhea (322). Furthermore, outbreaks of nosocomial VRE are most common in renal, liver, hematology, and intensive care units where glycopeptide therapy is common. A further source of glycopeptide “pressure” is the use of the antibiotic avoparcin in animal husbandry. Avoparcin is a glycopeptide related to vancomycin that is not used in human therapy but that is added in small amounts to animal feeds in Europe. Several studies suggest that in farms where avoparcin additives are used, animal and human bowels become colonized with vanA-type VRE, and frozen chickens in supermarkets may be a source of VRE for people unexposed to hospitals or glycopeptides (323, 324). After admission to hospital, treatment with glycopeptides may select these microorganisms from the bowel with resulting nosocomial infection (325). As a result of these studies, several European countries have now banned avoparcin feed supplements, but this issue remains controversial. Avoparcin is not used in the U.S., which has the greatest incidence of VRE and where transmission appears to be mainly healthcare-associated. The reasons for the differences in epidemiology of VRE between Europe and the U.S. has not been fully elucidated (326, 327). Multiply Resistant Pneumococci Streptococcus pneumoniae is the most common cause of bacterial pneumonia, the second most common cause of meningitis, the third most common cause of septicemia, and an important pathogen of otitis media (71, 328); all of these are predominantly community-acquired infections. Until recently, the pneumococcus was fully sensitive to benzylpenicillin and not often considered an important hospital pathogen. However, the pneumococcus does cause hospital cross-infection (329), and hospital outbreaks with multiply resistant strains (which are more readily recognized) are being reported with increasing frequency. Transmission is presumably by droplet spread, and ideally, infected patients should be nursed in side rooms (329). S. pneumoniae frequently acquires resistance to tetracycline and sometimes to sulfonamides, erythromycin, lincomycin, or chloramphenicol. Pneumococci are normally relatively resistant to aminoglycosides (MICs of streptomycin 8 Вg/mL), but some strains show high-level resistance (>2,000 Вg/mL) (287). Penicillin resistance was first reported in 1967 from Papua New Guinea, and since then has been seen with increasing frequency in many countries (328, 330). Multiple resistance is an increasing problem, the most commonly seen patterns being resistance to penicillin and tetracycline and resistance to penicillin, tetracycline, and chloramphenicol. Sensitive strains of pneumococci have penicillin MICs of 0.006 to 0.008 Вg/mL. The first penicillin-resistant isolates showed low-level resistance with MICs of 0.1 to 1.0 Вg/mL, but in 1977 pneumococci were isolated in South Africa showing high-level resistance with penicillin MICs of more than 1 Вg/mL (331). Penicillin resistance results from the stepwise acquisition of multiple genetic changes that produce various alterations in pneumococcal PBPs (332). The variant sequences inserted into the PBP genes appear to have been derived by transformation from oral streptococcal species (333). Although many penicillin-resistant isolates of pneumococci are sensitive to newer ОІ-lactams such as cefotaxime, some strains are resistant to these P.1626 drugs by producing simultaneous changes in more than one penicillin-binding protein (334, 335). Penicillin resistance in pneumococci may not be detected by routine sensitivity-testing methods, and for disk testing, a 1-mg oxacillin disk is recommended (336, 337). The geographic variation in the distribution of resistant strains of pneumococci is considerable, even between different cities in the same country, but accurate data are lacking. In the EARSS (87) study of resistance rates in European blood isolates, the rates of reduced penicillin susceptibility in pneumococci varied from <3% (usually in Northern European countries) to >30% (usually in Mediterranean countries). In the NNIS system surveillance report for 2002 (Table 91.1), penicillin resistance rates in nosocomial isolates were around 20% for both ICU and non-ICU patients. In some places there have been dramatic increases in penicillin resistance rates; in Cadiz, Spain, for example, high-level penicillin resistance was 29% in 1991 and 75% in 1995; in Hong Kong, China, penicillin-resistance was seen in 6.6% of sputum isolates in the first quarter of 1993 and in 56% of isolates in the second quarter of 1995; and in Kentucky, 53% of childhood community isolates were penicillin-resistant and 33% high-level resistant (338, 339, 340). Penicillin-resistant strains of pneumococci are also usually multiply resistant to other antibiotics. Since the early 1980s, many reports have appeared of hospital outbreaks of penicillin-resistant pneumococci (328, 341, 342, 343, 344, 345). These outbreaks often involve children or the elderly in day-care or chronic-care centers. In these age groups, nasal carriage is common, and during outbreaks other patients, staff members, and family members may become rapidly colonized by resistant pneumococci after casual contact with affected patients. Carriage may persist for several months, and the microorganisms may then disseminate further within the community. The prevention and control of hospital outbreaks depend on early detection, isolation, and treatment of infected cases. Infected patients should be isolated, and strict attention should be paid to hand washing. Visitors should be carefully supervised. During an outbreak, patients and staff members should be screened for nasopharyngeal carriage, and carriers should be cohorted or removed, as in the control of MRSA. Attempts should be made to eliminate nasal carriage with topical agents such as mupirocin and erythromycin, depending on the microorganism's sensitivity. Respiratory infections with strains of pneumococci showing low-level penicillin resistance can be treated with high doses of penicillin. Meningitis and infections with high-level resistant strains have been successfully treated with vancomycin or third-generation cephalosporins such as cefotaxime or ceftriaxone (346, 347). However, resistance to third-generation cephalosporins has increased dramatically in some areas (348), and there have been failures with these regimes in meningitis, and the combination of vancomycin with cephalosporins, meropenem, or rifampin has been recommended (349). Treatment with other antistaphylococcal agents such as erythromycin, chloramphenicol, lincomycin, or rifampin should be guided by the results of sensitivity testing. CONTROL OF ANTIBIOTIC-RESISTANT NOSOCOMIAL INFECTION Control of Antibiotic Use The correct use of antibiotics, as for all therapeutic drugs, includes the choice of agents that are necessary, effective, and safe. However, antibiotic therapy is unique, because it is directed against bacteria rather than patients, because it may be used to prevent as well as to cure disease, and because every treatment disturbs the human and environmental microflora of the hospital. In particular, correct use must take account of the potential effects on the development of antibiotic resistance. McGowan (18), in his extensive review of antibiotic use and antibiotic resistance, concluded, “Consensus rarely exists on topics in infectious disease. Yet, authors of virtually all of the papers reviewed here [68 references] agree on the need for careful, discriminating use of antibiotics as being the keystone of our attempts to control resistant bacteria in the hospital.” Nevertheless, many studies have shown that antibiotic use in hospitals is far from ideal (350, 351). Reports from U.S. hospitals have shown that 25% to 40% of hospital patients receive systemic antibiotics, with the proportions tending to rise in later surveys (351, 352, 353, 354, 355, 356, 357, 358, 359). Many patients receive antibiotics unnecessarily, and on surgical units 38% to 48% of treated patients have no evidence of infection (353). Similar patterns of use have been noted in British hospitals, in which about 20% to 30% of patients receive antibiotics and about 40% of courses are for prophylaxis (360, 361, 362, 363). In U.S. studies, 30% to 70% of all antibiotic courses were judged inappropriate (353). Other studies have shown that intravenous and prophylactic therapy is often unnecessarily prolonged and that the timing of prophylaxis is often inappropriate (312, 357, 358, 364). Some of this antibiotic misuse results from inadequate knowledge and poor understanding of antimicrobial therapy on the part of physicians. This can be attributed both to failures of education in medical schools and hospitals and the influence of specific product-related information from the pharmaceutical industry. Physicians probably get most of their information on antibiotics from pharmaceutical companies, and this needs to be balanced by impartial guidance from independent microbiologists and infectious diseases physicians (354). The results of educational programs aimed at improving use have varied, but they can be successful, especially when they are combined with audit of antibiotic use and feedback of results (365). Numerous strategies have been proposed to improve antibiotic use in hospitals (351, 353, 354, 366, 367, 368). A multidisciplinary group of experts in the U.S. was formed to develop strategies to prevent and control the emergence of antibiotic resistant microorganisms in hospitals (369). They proposed five strategic goals to optimize antimicrobial use, to optimize antimicrobial prophylaxis for surgery, to optimize choice and duration of empirical therapy, to improve prescribing by education, to monitor and feedback information on antimicrobial resistance rates, and to produce protocols for antibiotic usage. Most authorities recommend the publication of a formulary that limits the agents available for prescription from the hospital pharmacy, and this may be supplemented by specific written P.1627 antibiotic guidelines or a hospital antibiotic policy. Separate policies may be needed for specialized units such as intensive care or hematology/oncology. Since antibiotic policies imply some loss of individual clinical freedom for the benefit of the hospital as a whole, they should be overseen by a hospital committee consisting of senior physicians, surgeons, microbiologists, and pharmacists, and with the power to implement its decisions. The committee needs to meet regularly to revise and update the hospital policy, which will change with changing circumstances. To facilitate such revisions, the committee should receive regular audit reports of antibiotic use (and expenditure) in different clinical services as well as trends in antibiotic resistance in nosocomial pathogens. Most hospital prescribing is done by junior staff members who have limited experience in antibiotic therapy. Antibiotic policies usually restrict the number of agents available from a given antibiotic class; this reduces confusion, allows staff members to gain expertise in a smaller number of drugs, helps preserve the effectiveness of newer agents, and reduces pharmacy costs. Older, cheaper, and well-established “first-line” antibiotics are unrestricted and can be prescribed by all staff members for simple infections. Prescriptions for the more expensive and powerful “second-line” or “reserve” drugs may require the countersignature of senior physicians, clinical justification to the pharmacy, or, as is often the case in North America, consultation with the infectious diseases service. Another effective way to promote sensible antibiotic prescribing is by “intelligent” laboratory reporting facilitated by pathology computer systems. First, the laboratory should test a limited number of appropriate antibiotics for each significant isolate. Second, only a few of the agents tested should be reported, if the microorganism is reasonably sensitive, beginning with the recommended first-line agents. Third, if the microorganism is unusually resistant, or if the isolate is likely to be clinically insignificant, a “please consult” message should be given on the report form in place of the microorganism sensitivities; this will reduce the temptation to treat isolates rather than infections and encourage consultation on the use of second- and third-line agents. Even when an antibiotic prescription is justified, therapy may be unnecessarily prolonged. One way to reduce the length of treatment is to implement “stop” policies in which the pharmacy automatically cancels an antibiotic prescription after 3 to 5 days unless it is specifically renewed by the ward physician. A large proportion of antibiotic use and misuse is for prophylaxis, and it is especially important to have clear policies in this area. The hospital antibiotic committee should review the scientific literature in each area of prophylaxis and issue guidelines for the choice of agent and the timing of administration. For most surgical prophylaxis, the antibiotic should be given just before surgery and continue for no more than 24 hours. Limitation of prophylaxis in this way will greatly reduce the pressure on antibiotic resistance as well as produce considerable cost savings. There is evidence in the literature that formal policies of rotation—or complete withdrawal—of certain antibiotics were useful in the past for dealing with the emergence of multiresistant microorganisms (370, 371, 372). Such policies usually were applied to problems of resistance in gram-negative bacteria at a time when relatively few effective agents were available. Nowadays, several antibiotic groups are active against gram-negative microorganisms, and such policies are not often required. Nevertheless, in some areas where gentamicin resistance in Enterobacteriaceae and pseudomonads has been a problem, but where microorganisms have remained susceptible to amikacin, hospitals have adopted a policy of exclusive use of amikacin (373, 374, 375). In these centers, this policy has resulted in a decrease in gentamicin resistance without a concomitant increase in amikacin resistance. However, most hospitals now find multiply resistant gram-positive bacteria to be the major problem in hospital infection. There may be a need in the future to rotate or restrict agents active against gram-positive bacteria in order to preserve the effectiveness of reserve drugs such as vancomycin. Hospital antibiotic policies emphasize restriction and conservation, especially of newer and more expensive agents. Pharmaceutical representatives inevitably have rather different goals. Open communication between physicians and the pharmaceutical industry is mutually beneficial and should be encouraged, but this should be monitored to ensure that commercial activity does not conflict with the established hospital antibiotic policy (354). Experience with antibiotic policies has shown that attempts to enforce restriction on antibiotic use will only ever have limited success. Rather, it is education that is the keystone of an effective antibiotic policy (356, 361). “Knowing when not to use an antibiotic is as important as knowing which antibiotic to choose” (366). Control of Hospital Infection After the reduction of unnecessary antibiotic use, the control of resistant bacteria in hospitals depends on the implementation of rational programs of infection control. As hospital pathogens become increasingly antibiotic-resistant, prevention of infection and spread assumes ever-greater importance. Infection control programs are the same for both sensitive and resistant bacteria and are dealt with in detail elsewhere in this book. However, several areas are of particular importance for the control of resistant microorganisms and are emphasized here. The U.S. consensus group that drew up five strategic goals for optimizing antimicrobial use referred to previously also proposed five strategic goals to detect, report, and prevent transmission of antibiotic resistant microorganisms in hospitals (369): to develop systems to recognize and report trends in resistance within hospitals; to develop systems to rapidly detect, report, and act on the presence of resistant microorganisms in individual patients; to improve compliance with basic infection control procedures and policies; to incorporate the detection, prevention, and control of antimicrobial resistance into institutional strategic goals; and to develop plans for identifying, transferring, discharging, and readmitting patients colonized with resistant microorganisms. Patients who have infection or asymptomatic colonization with antibiotic-resistant bacteria should be carefully assessed and isolated if necessary, and staff should pay strict attention to hand washing. Urinary catheterization is associated with considerable risk of cross-infection with resistant microorganisms, and staff members should follow hospital policies for urinary catheter P.1628 care. Similarly, policies for the insertion, management, and removal of vascular catheters should be followed to reduce infection with resistant skin bacteria. As described previously, gram-negative opportunistic pathogens are often inherently antibiotic- and disinfectant-resistant and may survive and proliferate in nutritionally poor environments. Thus, they contaminate diluted disinfectants and medications and wet environmental sites such as ventilator, humidifiers, water systems, sinks, and drains. Programs should be instituted to ensure clean and safe disinfectants (376); reliable methods to decontaminate hospital equipment and environmental sites should be established; and single-use or individual medications, creams, jellies, and ointments should be employed. The value of surveillance or screening cultures is debated. Most authorities believe that routine environmental cultures are unnecessary and that environmental screening should be done only during searches for the source of an outbreak, and then only under the supervision of the infection control staff. It should be remembered that infected or colonized patients are often the sources of environmental contamination and that random sampling may reveal resistant environmental microorganisms that have no clinical significance. Screening of patients, and sometimes of staff members, is more useful. During an outbreak, many patients and staff members may become asymptomatic carriers of resistant microorganisms—for example, with MRSA or multiply resistant Klebsiella. Control of such epidemics requires that colonized patients and staff members be isolated (or removed from work) until cleared of carriage. Under these circumstances, screens should be repeated until all carriers have been eliminated and the outbreak has been controlled. Surveillance screening in the absence of an outbreak is more contentious (377). It is well recognized that patients and staff members from other hospitals known or suspected of being affected by epidemic-resistant pathogens with high epidemic potential such as MRSA should be screened for carriage before being allowed in general ward areas. When patients are admitted from other hospitals to high-risk areas such as oncology or intensive care units, they should also be screened for stool carriage of multiply resistant, gram-negative bacteria. Some specialized wards such as neonatal or bone marrow transplantation units, especially those that have recurrent problems with multiply resistant pathogens, might wish to screen patients (nasopharynx, moist skin sites, rectum, and vagina) at weekly intervals. This should be done only after discussion with the infection control team, and the specific pathogens being sought should be carefully defined (377). SELECTIVE DECONTAMINATION OF THE DIGESTIVE TRACT In intensive care patients, the most common site of infection is the lower respiratory tract, common pathogens are multiresistant aerobic gram-negative bacilli, and the most common source is the patient's own oropharynx colonized by microorganisms from the hospital environment. Some colonization may be due to endogenous multiresistant microorganisms brought in by the patient from the community and then encouraged to proliferate by hospital antibiotic pressure (61, 107, 144, 378). This type of infection carries a high mortality rate in compromised patients, and attempts have been made to reduce its incidence by selective decontamination of the digestive tract (SDD). In this procedure, intravenous and topical antibiotics are used in high-risk patients (especially ventilated patients on ICUs) to prevent colonization of the oropharynx and gut by potentially pathogenic bacteria and yeasts. SDD regimes are designed to kill aerobic gram-negative bacteria and (often) fungi while preserving the normal anaerobic flora. Most SDD regimes are successful in reducing oropharyngeal colonization with aerobic gram-negative bacteria and encouraging their replacement with gram-positive aerobes (379, 380). Because of this, gram-negative infections may be replaced by gram-positive ones, including infection with multiply resistant strains (381, 382, 383), and some authorities now recommend the addition of vancomycin to standard regimes (382). Some studies and meta-analyses of SDD have shown a reduction in the rates of respiratory tract infection and mortality (384) but some double-blind trials have indicated no obvious benefit (385). Unfortunately, many different SDD regimes are used, and many studies of their effectiveness have been poorly designed. The value of the new vancomycin regimes needs to be properly assessed by controlled trials, and the danger that the widespread use of SDD antibiotics might encourage, rather than prevent, the emergence of resistant bacteria in ICUs needs further study. The case for routine SDD to prevent multiresistant gram-negative infections in high-risk patients has not yet been proven. SDD may turn out to be more useful for controlling established outbreaks of resistant bacteria (386, 387). CONCLUSION Antimicrobial resistance, often multiple, has spared few nosocomial pathogens, and despite overreporting, is increasing inexorably. Some have suggested that the emergence of essentially untreatable nosocomial pathogens, such as multiresistant gram-negative bacilli and VRE, signifies a crisis for antimicrobial therapy and heralds the end of the antibiotic era (1, 47, 388). 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The vast majority of antimicrobial agents employed in clinical settings are either natural products or chemical derivatives of natural products. The producers of these agents in nature are generally the microbes themselves, and their development appears to represent an attempt to acquire a selective advantage in mixed microbial environments. Since the production of antibiotics has been occurring in the microbial environment for (presumably) eons, it stands to reason that mechanisms to avoid their lethal action have been developed as well, either by species that produce the antibiotics or those that must share limited space and resources with those that do. In many instances, therefore, our discovery and growing use of antibiotics has led not to the development of resistance genes in bacteria, but merely to the natural selection of intrinsically resistant species or the efficient scavenging of preexisting resistance genes by normally susceptible human pathogens. The emergence of Lactobacillus species during therapy with vancomycin and of Stenotrophomonas maltophilia during therapy with imipenem are examples of selection of intrinsically resistant species. Other phenotypes of resistance reflect more the ease with which susceptible bacteria can mutate either structural or regulatory genes intrinsic to their species in a manner that results in decreased antibiotic susceptibility. Examples of this type of resistance include extended-spectrum cephalosporin resistance in Enterobacter species, fluoroquinolone resistance in many different species of bacteria, or the emerging resistance to linezolid in enterococci. Resistance to some antibiotics, in some species, is not readily achievable by mutation, and thus must be acquired from other sources. This so-called acquired resistance accurately characterizes many different resistance phenotypes, including ampicillin-resistance in Escherichia coli, penicillin-resistance in staphylococci, and vancomycin resistance in enterococci and more recently in Staphylococcus aureus. Finally, when antimicrobial agents are developed specifically to avoid the lethal action of acquired resistance genes, mutations within the acquired genes themselves can lead to resistance to the newer agents. The emergence of resistance to extended-spectrum cephalosporins in Klebsiella pneumoniae and E. coli represent this sort of amplified resistance. Antimicrobial agents are effective, because they target metabolic pathways or enzymes that are specific to bacteria and not to the host. A variety of mechanisms have been shown to result in bacterial resistance. Among these mechanisms are alterations in the antibiotic target such that binding or inhibition of function is decreased to the point of clinical irrelevance, decreased permeability that results in the inability of the agent to reach its target at a critical concentration, efflux of the agent from the cell, and destruction or modification of the antibiotic. The expression of resistance and virulence by bacteria is often linked, but sometimes in unpredictable ways. Selection of rifampin or streptomycin-resistant mutants in the laboratory is often associated with a decrease in the virulence of the strains when tested in animal models (1). It is presumed that the point mutations in the targets (RNA polymerase in the case of rifampin, the ribosome in the case of streptomycin) lead to subtle but not fatal decreases in function in these resistant strains, conferring a competitive survival disadvantage relative to wild-type strains. Interestingly, continued passage in animals in the absence of antibiotic selective pressure does not always result in reversion to the susceptible genotype. Instead, compensatory mutations frequently occur that mitigate the deleterious affects of the primary mutation, restoring virulence while maintaining resistance (1). Acquired resistance and virulence determinants may also coalesce in environments that favor them, such as the modern hospital. Recent reports suggest that ampicillin- and vancomycin-resistant Enterococcus faecium strains isolated in United States hospitals are enriched in potential virulence determinants esp (enterococcal surface protein) and hyaluronidase (2, 3). This combination of resistance and virulence may help explain the remarkable increase in importance of E. faecium as a nosocomial pathogen over the past decade (4, 5). ANTIMICROBIAL RESISTANCE TRANSFER Although the primary concern of the hospital epidemiologist is the prevention of spread of bacterial strains among hospitalized patients, it is worthwhile to consider mechanisms by which resistance genes themselves can spread among bacterial strains. A full discussion of the mechanisms of resistance transfer is beyond the scope of this chapter. Nevertheless, a few basic concepts should be understood. P.1594 Antimicrobial resistance determinants are commonly incorporated into extrachromosomal, independently replicating elements known as plasmids. Plasmids vary greatly in size (3 to >200 kb) and in the number of incorporated resistance determinants. In addition to genes responsible for replication and for antibiotic resistance, many plasmids also possess genes that stimulate their transfer between strains within a given genus, and occasionally between strains of different (although usually closely related) genera. Large, transferable plasmids have been implicated in the spread of ceftazidime resistance among strains of Enterobacteriaceae, particularly in intensive and chronic care settings (6, 7). Many of these plasmids also possess genes encoding resistance to a range of non–β-lactam antimicrobial agents, resulting in the elimination of several antibacterial options with a single transfer event (6, 7). Transferable plasmids have also been identified in gram-positive genera, perhaps best characterized by the pheromone-responsive plasmids found in strains of Enterococcus faecalis (8). The widespread emergence of high-level gentamicin resistance in enterococci (see below), resulting from the production of a modifying enzyme most commonly encoded on plasmids, is a testament to the efficiency of plasmids in disseminating resistance determinants in this genus (9, 10). Enterococci are also known to possess “broad host range” plasmids. These plasmids transfer at a lower efficiency than do the pheromone-responsive plasmids, but have the advantage of being able to transfer to and replicate within a wide variety of species. Recent evidence implicates broad host-range plasmids in the exchange of important resistance genes between enterococci and staphylococci, including ОІ-lactamase production and high-level vancomycin resistance (11, 12, 13). Plasmids need not encode their own transfer genes in order to spread between strains. Nonconjugative plasmids may be mobilized for transfer by conjugative plasmids. In addition, the presence of insertion sequences (small regions of DNA capable of independent movement between replicons) has been shown to facilitate the co-integration of conjugative and nonconjugative plasmids, resulting in a larger, conjugative element (14). Appropriately sized plasmids may also be spread by transduction, resulting from the aberrant incorporation of plasmid rather than bacteriophage DNA into the phage head. In addition to plasmids, antimicrobial resistance determinants frequently are incorporated into mobile elements known as transposons. Transposons may be rather simple elements whose mobility results from the presence of insertion sequences flanking an antimicrobial resistance determinant (composite transposons), an arrangement in which mobility is due entirely to functions encoded by the insertion sequences (15). Alternatively, transposons may be complex structures incorporating several genes. Tn21 is a Tn3-family transposon that has been found to contain a genetic locus (tnpI) that serves as a “hot spot” for the integration of a variety of antimicrobial resistance genes (16). Consequently, several Tn21-like transposons conferring resistance to a number of different antimicrobial agents, in varying combinations, have been described (17). These loci, referred to as integrons, appear to be important mechanisms for the dissemination of antimicrobial resistance genes in many gram-negative bacilli (18, 19). Recent data indicate that integrons may be critical vehicles of microbial genetic evolution, and have only recently been employed by bacteria for purposes of stockpiling resistance determinants (20). Another Tn3-family transposon, Tn1546 (21), confers resistance to vancomycin and teicoplanin in enterococci and more recently in S. aureus. It encodes nine genes involved in the regulation of transposition and the expression of glycopeptide resistance. In general, transposons participate in the transfer of antimicrobial resistance determinants by virtue of their ability to move between bacterial chromosome and transferable plasmid. Exceptions to this rule are the conjugative transposons of gram-positive bacteria, which can transfer between strains without the necessity of a plasmid intermediate (22). These transposons possess their own genes responsible for transfer between microorganisms. In general, conjugative transposons encode resistance to tetracycline via the tetM gene, although some have been found to encode resistance to multiple antimicrobial agents (22). In addition to the transfer of the elements themselves, some investigators have found that the presence of conjugative transposons stimulates the transfer of unrelated chromosomal genes, raising the possibility that these elements could be involved in the transfer of a range of unrelated resistance determinants (11, 23). A transposon in the Tn916 family has been described that encodes VanB-type vancomycin resistance in E. faecium (24). Conjugative transposons may also transfer determinants for antibacterial activity as well as antibiotic resistance. Several lactococcal conjugative elements encoding determinants for production of the antibacterial peptide nisin have been described (25). Other mobile elements involved in the spread of antimicrobial resistance are the insertion sequences (IS elements). These elements do not encode antimicrobial resistance themselves but may aid in the spread of resistance determinants via the formation of composite transposons or by serving as areas of homologous recombination between plasmid and chromosome. Insertion of IS elements may also result in the activation of poorly expressed genes via the presence of promoter sequences within the end of the mobile element (15). Evidence indicates that the expression of imipenem resistance in some strains of Bacteroides fragilis is due to the insertion of IS elements upstream of an unexpressed chromosomal gene encoding a carbapenemase (26). Our ability to thwart the spread of resistance determinants between bacterial strains in the natural environment is, at present, poor. Factors affecting transfer between strains are poorly understood, but in some cases may involve exposure to antimicrobial agents themselves. Transfer of conjugative transposons, for example, has been shown to be increased in vitro and in vivo after exposure of the donor strain to tetracycline (27, 28). It is therefore reasonable to presume that environmental pressure from the overuse of antimicrobial agents plays some role in the spread of these determinants. In addition, the commingling of many different strains of bacteria in the human gastrointestinal tract resulting from hospital and antibiotic exposure as well as from inattention to appropriate infection control techniques probably play roles in the spread of resistant strains. In some cases, institution of infection control measures (such as barrier precautions for infected and colonized patients) has been shown to abort serious outbreaks of resistant microorganisms (29, 30). In others, decreasing use of an antibiotic has been associated with a reduction in the prevalence of resistant strains in an institution (31). P.1595 As such, judicious use of antimicrobial agents and proper attention to infection control recommendations are likely to be our best weapons to combat the spread of resistant bacteria for the foreseeable future. ОІ-LACTAMS Mechanism of Action Targets of ОІ-lactam antibiotics are a series of enzymes involved in the last step of peptidoglycan (cell wall) synthesis. This step involves a cross-linking reaction carried out by transpeptidases in which the terminal D-alanine of the pentapeptide stem of the peptidoglycan is cleaved. The energy resulting from this cleavage is used to form a peptide bond between the fourth residue of the pentapeptide (also D-alanine) and the cross-bridge, which is itself linked to the e-amino of diaminopimelic acid (in gram-negative microorganisms) or lysine (in gram-positive microorganisms) (Fig. 90.1). This cross-link is absolutely required for structural integrity of the bacterial cell wall. ОІ-Lactam antibiotics, such as penicillin, are structural analogs of the pentapeptide terminal D-alanyl:D-alanine (Fig. 90.2) target covalently bound by the transpeptidases. The fact that these transpeptidases also bind penicillin (and other ОІ-lactams) covalently has resulted in referral to them as penicillin-binding proteins (PBPs). Figure 90.1. Structure of murein in bacteria. The gram-positive pentaglycine cross-link is shown. (From Schaechter M, et al., eds. Mechanisms of microbial diseases, 2nd ed. Baltimore: Williams & Wilkins, 1993.) Figure 90.2. Stereochemical models comparing penicillin (A) and the D-alanyl-D-alanine terminus of the peptidoglycan (B). Arrows indicate the position of the CO–N bond in the -lactam ring of penicillin and of the CO–N bond in the D-alanyl-D-alanine. (Adapted from Volk WA, et al., eds. Essentials of medical microbiology. Philadelphia: JB Lipp3incott, 1991.) Figure 90.3. Reactions catalyzed by ОІ-lactamase on penicillin and on cephalosporin. (From Neu HC. Contribution of ОІ-lactamases to bacterial resistance and mechanisms to inhibit ОІ-lactamase. Am J Med 1985;79(suppl 5B):2–12.) Mechanisms of ОІ-Lactam Resistance Target Resistance The binding affinity of ОІ-lactams for their targets, the PBPs, varies with the ОІ-lactam and the PBP. Enterococci, for example, are intrinsically resistant to the cephalosporins, because these ОІ-lactams do not bind the enterococcal PBPs with high affinity (32). Within the genus Enterococcus, E. faecium tend to be more resistant to penicillins, because many strains express a low-affinity PBP (PBP5) that carries out cell wall synthesis at penicillin concentrations that inhibit the other PBPs (33). Many cases of PBP-mediated ОІ-lactam resistance result from the intrinsic characteristics of the PBPs of a given strain. PBP-mediated resistance may also be acquired. Resistance resulting from mutation can be readily demonstrated in the laboratory (34). Resistance to oxacillin in clinical S. aureus strains has been attributed to point mutations in PBP genes (34). In species that are naturally transformable (that can absorb naked DNA from the environment), formation of mosaic PBP genes is common. Cloning and sequencing of Streptococcus pneumoniae or Neisseria gonorrhoeae genes encoding abnormal, low-affinity PBPs responsible for penicillin resistance has shown significant sections of these genes to be of foreign origin. In S. pneumoniae, the origin P.1596 appears to have been from oral streptococci (35); in N. gonorrhoeae, from oral commensal neisserial species (36, 37). The evolution of mosaic genes most likely occurred via DNA transformation followed by homologous recombination across areas of PBP sequence homology between the native and foreign DNA. Entire low-affinity PBPs can also be acquired by normally susceptible bacteria. Methicillin-resistant S. aureus (MRSA) has most commonly acquired low affinity PBP2a, encoded by the mecA gene. Recent work suggests that the mec region is located within a larger mobile element (designated SCCmec) and that this region varies in size depending on how much extra DNA it contains (38). Nosocomial strains (which are resistant to several unrelated classes of antimicrobial agents) contain a larger SCCmec, reflecting insertion of additional DNA, some of which encodes additional antimicrobial resistance. In contrast, the recently described MRSA arising in the community (which is generally susceptible to a range of other antimicrobial agents) contains a relatively small SCCmec that encodes only resistance to methicillin (39). Recent data suggest that the mec region may have been acquired from coagulase-negative staphylococcal species (40). The expression of resistance encoded by mosaic or acquired PBPs is often dependent on very specific conditions. Several staphylococcal genes, called fem (factors essential for methicillin resistance) or aux factors, have been identified, the inactivation of which results in reversion to susceptible phenotype despite expression of PBP2a (41). In most cases these fem genes encode enzymes responsible for the synthesis of peptidoglycan precursors. The failure to express resistance when these genes are deleted suggests that the PBP2a is very specific in the substrates it will tolerate. Similar supportive genes have been described in S. pneumoniae strains that encode mosaic PBP genes (42). Enterococci are intrinsically resistant to some ОІ-lactams, especially the cephalosporins, at high levels. Resistance is related to the low affinity of these compounds for the enterococcal PBPs (33, 43). Strains resistant to even higher levels of the penicillins, in the absence of production of ОІ-lactamase, have been described with increasing frequency (4, 44). These strains include several species, but E. faecium is most commonly reported from clinical laboratories. Most of these high-level resistant strains possess one or more point mutations in pbp5 that are thought to lower the affinity for penicillin and other ОІ-lactams (45). It is not clear at present whether the point mutations alone account for all of the penicillin resistance in these strains (46). Enterococcal strains expressing high levels of resistance to ОІ-lactams through low-affinity PBPs are also more resistant to ОІ-lactam–aminoglycoside synergy, even in the absence of high levels of aminoglycoside resistance (47). Single-agent ОІ-lactam therapy is precluded for such strains, leaving the glycopeptides as the antibiotic class of choice. The continued spread of glycopeptide resistance in penicillin-resistant enterococci (see below) is a persistent problem at many large centers (4). ОІ-Lactamase–Mediated Resistance A more important and frequent mechanism of bacterial resistance to ОІ-lactam antibiotics, especially in gram-negative bacteria, is the production of ОІ-lactamases, enzymes that hydrolyze the ОІ-lactam ring (Fig. 90.3). The reactive ОІ-lactam ring is required for formation of a covalent bond between the antibiotic and its PBP target. Destruction of this ring results in loss of antimicrobial activity. The ОІ-lactamases form a broad family of enzymes, and along with the PBPs, are classified as serine D, D-peptidases (48). The homologies between many ОІ-lactamases and PBP have led to the suggestion that ОІ-lactamases have evolved from penicillin-binding proteins. Two classification schemes for the ОІ-lactamases are widely used. The first is based on primary structure and has been proposed by Ambler et al. (49) (Table 90.1). In this scheme, the enzymes of staphylococci, the common plasmid-mediated enzymes of the gram-negative microorganisms and all their variants, one of the enzymes of Bacillus, and others are lumped into a single class, class A. A consensus sequence for this class has been proposed (50). The other scheme (Bush-Jacoby-Medeiros classification) relies on the substrate specificity of the enzymes (51) (Table 90.2). There are many more classes and subclasses in this scheme, since single point mutations in the gene encoding an enzyme may result in substantial changes in substrate specificity. TABLE 90.1. MOLECULAR CLASSIFICATION OF ОІ-LACTAMASES Class Examples A TEM, SHV (gram-negative microorganisms), PC1 (Staphylococcus aureus) B Metallo-ОІ-lactamases C AmpC gene D OXAT-4 From Ambler R.P. The structure of ОІ-lactamases. Philos Trans R Soc Lond [B] 1980;289:321-331, with permission. TABLE 90.2. CLASSIFICATION OF ОІ-LACTAMASES ACCORDING TO FUNCTION Group Description Examples Molecular Class 1 Cephalosporin hydrolyzing enzymes not inhibited by clavulanic acid AmpC C 2a Penicillin hydrolyzing enzymes inhibited by clavulanic acid B. licheniformis 749 A 2be Broad-spectrum enzymes inhibited by clavulanic acid TEM A 2b Extended-spectrum enzymes inhibited by clavulanic acid TEM 3-26 A 2c Carbenicillin hydrolyzing enzymes inhibited by clavulanic acid PSE-1.3.4 A 2d Cloxacillin hydrolyzing enzymes inhibited by clavulanic acid OXA-1-11 D 2e Cephalosporin hydrolyzing enzymes inhibited by clavulanic acid B. fragilis G42 A 3 Metallo-ОІ-lactamases S. maltophilia GN12873 B 4 Penicillin hydrolyzing enzymes not inhibited by clavulanic acid B. fragilis G237 ? From Bush K, Jacoby GA, Medeicos AA. A Functional Classification Scheme for b-lactamases and its molecular structure. Antimicrob Agents Chemoth 1998;39:1216. Staphylococcal ОІ-lactamase production became widespread P.1597 within a few years of the clinical introduction of penicillin (52, 53). By the mid-1940s, ОІ-lactamase–producing S. aureus strains were widespread within hospitals, necessitating the introduction of vancomycin and semisynthetic penicillins such as methicillin, nafcillin, and oxacillin. Although the subsequent decades have not seen significant evolution of the staphylococcal genes resulting in hydrolysis of the semisynthetic penicillins or new cephalosporins, it has been shown that the most common variant of staphylococcal ОІ-lactamase, immunologic type A, is more efficient at hydrolyzing older cephalosporins such as cefazolin, a fact that may be related to failures of antibiotic prophylaxis in some cases (54). The commonly used semisynthetic penicillins are highly effective in treatment of infections due to methicillin-susceptible, ОІ-lactamase–producing staphylococci, as are combinations of ОІ-lactams and ОІ-lactamase inhibitors. The importance of ОІ-lactamase production in gram-positive bacteria remains essentially restricted to staphylococci. Among other gram-positive pathogens, only enterococci have been shown to express ОІ-lactamase (the same ОІ-lactamase as expressed by staphylococci), but reports of such isolates remain quite rare and their clinical importance appears to be minimal. The epidemiology of ОІ-lactamase–mediated resistance in gram-negative bacilli is far more complex than in gram-positive. Hundreds of different ОІ-lactamases have been described in gram-negative bacteria over the past two decades. The most problematic and prevalent of these enzymes are those that confer resistance to expanded spectrum cephalosporins. Many of these extended-spectrum ОІ-lactamases (ESBLs) are progeny of more narrow spectrum enzymes that fall, like the staphylococcal ОІ-lactamase, into Ambler class A. The most common enzymes of this class among clinical isolates are related to the widely prevalent TEM-1 and SHV-1 enzymes (51). TEM-1 is widely prevalent as the cause of ampicillin resistance in E. coli, Haemophilus influenzae, and in some cases N. gonorrhoeae, whereas SHV-1 is the chromosomal ОІ-lactamase found in most K. pneumoniae strains. TEM-1 and SHV-1 are broad-spectrum ОІ-lactamases that hydrolyze the penicillins (ampicillin, mezlocillin, and piperacillin) with greater efficiency than the cephalosporins (55). Genes encoding ESBLs are most commonly found on transferable plasmids with resistance determinants to numerous other antimicrobial classes. Since the early 1980s, we have observed the emergence of K. pneumoniae and E. coli, and occasionally other Enterobacteriaceae, producing mutant forms of TEM-1 or SHV-1 capable of hydrolyzing the oxyiminocephalosporins (ceftazidime, cefotaxime, ceftriaxone), aztreonam (a monobactam), and others (55). Although TEM-related enzymes predominated in early ESBL outbreaks, more recent surveys suggest a predominance of SHV-related ESBLs. Moreover, an increasingly greater variety of non–TEM- or SHV-related enzymes continue to be described (56). Strains elaborating ESBLs, most commonly Klebsiella, have been responsible for several outbreaks of infection and colonization in Europe and the U.S. More recently, several different ESBLs have been described in Proteus mirabilis, especially in Europe (57). Outbreaks have been ascribed to clonal dissemination, plasmid dissemination, or both (31, 58, 59). The expanded activity of ESBLs results from single or sometimes multiple point mutations in the genes that result in critical amino acid substitutions (55). These point mutations are often found in association with cellular characteristics that serve to enhance the phenotypic expression of resistance, such as location downstream of strong promoters (leading to increased ОІ-lactamase quantity) and reductions in the expression of outer membrane proteins (porins that serve as conduits for entry of antibiotics into the periplasmic space). These enhancing mechanisms may be important predisposing factors for the emergence of ESBLs in the clinical setting, since they would be expected to increase expression of resistance at the single cell level, thereby promoting the survival of initial point mutants in the setting of heavy antibiotic exposure. At least one case study supports the concept of predisposing porin reductions promoting emergence of an ESBL (60). Mutations to extend the spectrum of TEM-1 or SHV-1 and P.1598 allow hydrolysis of extended-spectrum cephalosporins commonly yield increased susceptibility to inhibition by ОІ-lactamase inhibitors. In the clinical setting, however, the production of multiple enzymes and/or overproduction of individual enzymes often confers in vitro resistance to ОІ-lactam/ОІ-lactamase inhibitor combinations in ESBL producers. The relative scarcity of ESBL producers has made controlled studies of the efficacy of different therapies impractical, but carbapenems have been most effective in animal studies of infections with ESBL producers as well as case reports and small series. The most clinical experience has been with imipenem (58, 61). Resistance to extended-spectrum cephalosporins may also be conferred by expression of regulatory mutants of Bush-Jacoby-Medeiros group 1 (Ambler's class C) ОІ-lactamases. These enzymes are broadly active cephalosporinases (which also hydrolyze penicillins) and resistant to clinically achievable concentrations of ОІ-lactam/ОІ-lactamase inhibitor combinations (51). They are encoded by the ampC gene, a chromosomal gene widely disseminated among Enterobacteriaceae and Pseudomonas aeruginosa. In some species, such as E. coli, ampC is poorly expressed and not under regulatory control due to the absence of the ampR gene. The product of the ampR gene interacts with different cell wall breakdown products in a manner that results in AmpR becoming either a suppressor or an activator of ampC transcription (62, 63, 64). Under normal circumstances, cells with inducible AmpC ОІ-lactamases employ AmpD (a cellular amidase encoded by ampD) to reduce intracellular quantities of cellular breakdown product anhydro-muramyl-tripeptide, which results in an excess of uridine diphosphate (UDP)-muramyl-pentapeptide. UDP-muramyl-pentapeptide interaction with AmpR maintains AmpR as a repressor of ampC transcription. When exposed to certain antibiotics that favor production of anhydro-muramyl-tripeptide (such as cefoxitin, clavulanic acid, and imipenem), the ability of AmpD to convert this substrate is overwhelmed, and interaction between anhydro-muramyl-tripeptide and AmpR converts AmpR into an activator of ampC transcription (induction). ampR is present and ampC is under regulatory control in Enterobacter species, Serratia marcescens, Citrobacter freundii, and P. aeruginosa, among others (64, 65, 66). Imipenem is an efficient inducer of ampC expression, but it is a poor substrate for the ampC ОІ-lactamase. It therefore remains active even in the presence of induced ОІ-lactamase (as long as a concomitant mutation decreasing the entry of imipenem into the periplasmic space is not present—see below). Newer cephalosporins such as ceftazidime, ceftriaxone, and others are efficiently hydrolyzed by the AmpC, but are poor inducers and therefore appear active in vitro against bacteria expressing inducible AmpC. Unfortunately, the newer oxyiminocephalosporins (e.g., ceftazidime, cefotaxime, ceftriaxone) are very good selectors of mutants that express high levels of the ampC ОІ-lactamase constitutively. Their ability to select constitutive mutants results from their status as weak inducers. Constitutive AmpC production commonly results from null mutations in ampD, with subsequent intracellular accumulation of anhydro-muramyl-tripeptide and constitutive activation of ampC expression (62). Thus, from among a population of microorganisms, the small number (1 in 106–7) of preexisting cells with mutations ampD are selected for growth by the presence of antibiotic with potent activity against strains in which ampC expression is repressed. Once constitutive expression occurs, the strains are essentially resistant to all ОІ-lactams except for carbapenems and cefepime (66). Cefepime's major advantage in this regard appears to be its status as a zwitterion, allowing it to achieve high periplasmic concentrations by rapid passage through the outer membrane. Caution should be exercised in using cefepime to treat deregulated ampC mutants of Enterobacter species, however, since reports of the emergence of cefepime resistance (associated with a reduction in an outer membrane protein) in these strains during therapy have been published (67). Although many ОІ-lactams can select for constitutive ampC mutants in vitro, third-generation cephalosporins are the primary offenders in the clinical setting (68, 69). In a study of Enterobacter bacteremia by Chow et al. (68), the major class of antibiotics associated with selection of resistance was the newer cephalosporins as opposed (especially) to the newer penicillins. Concomitant use of aminoglycosides did not prevent the emergence of this resistance. In this study, resistance developed in 19% of all patients treated with newer cephalosporins. Therapeutic failure occurred in about half of those patients. For all patients infected with a multiply resistant strain, the mortality rate was significantly increased. Infection with a multiply resistant strain was closely associated with prior use of a new cephalosporin. These data argue for limiting the use of extended-spectrum cephalosporins to forestall the emergence of Enterobacteriaceae resistant to multiple ОІ-lactam antibiotics. Although ampC is chromosomally encoded and generally not transferable, plasmid-encoded versions of these enzymes have been observed in several species of Enterobacteriaceae, including E. coli and K. pneumoniae, among others (56). These strains express high levels of the AmpC enzyme constitutively and have resistance profiles identical to multiply ОІ-lactam–resistant Enterobacter species and P. aeruginosa. The most prevalent of these enzymes is CMY-2, derived from the Citrobacter AmpC enzyme (70). Plasmid-encoded AmpC enzymes have been found in E. coli, Salmonella, and other gram-negative species (56). Currently available ОІ-lactamase inhibitors are poorly active against these enzymes. Thus, the carbapenems are the only therapeutically reliable ОІ-lactams. It is noteworthy, however, that one such enzyme, designated ACT-1, was identified in a porin-deficient strain of K. pneumoniae, where it conferred resistance to imipenem and was associated with failures of this antibiotic in clinical settings (71). Resistance to ОІ-lactam/ОІ-lactamase inhibitor combinations can result from several different mechanisms, all of which involve the production of ОІ-lactamase. As noted above, expression of an AmpC enzyme confers resistance to both cephalosporins and ОІ-lactam/ОІ-lactamase inhibitor combinations. Resistance to inhibitor combinations alone can be conferred by increased production of a normally susceptible enzyme (i.e., TEM-1), permeability defects, or a combination of both mechanisms (72). Specific inhibitor-resistant enzymes can also result from mutation of TEM-1 or SHV-1, similar to extending the cephalosporin spectrum of these ОІ-lactamases (73). Although mutations that extend the spectrum against cephalosporins and those that confer resistance to inhibitors are not strictly incompatible, the extent of resistance conferred against one class of compounds is usually P.1599 mitigated by the concomitant presence of mutations conferring resistance to the other class (74). These data indicate that the active site of class A enzymes is limited in its flexibility, and that mutations that extend the natural spectrum come at a cost in enzyme efficiency. Human pathogenic bacteria seem to have figured this out by themselves, however, since resistance to both extended-spectrum cephalosporins and ОІ-lactam/ОІ-lactamase inhibitor combinations is quite common in the clinical setting. This phenotype can be conferred by production of AmpC enzymes, by the increased production of an ESBL, or by the expression of more than one enzyme (one an ESBL, the other a more common enzyme such as SHV-1) (75, 76). Although the carbapenems remain the most stable ОІ-lactams to hydrolysis, there are specific enzymes that are efficient at hydrolyzing these compounds. S. maltophilia is an intrinsically carbapenem-resistant species that can emerge as an important pathogen in clinical settings (77). It owes its resistance to synthesis of an inducible, zinc-dependent carbapenemase encoded on the chromosome. Several cation (usually zinc)-dependent ОІ-lactamases (generally classified as IMP or VIM enzymes) capable of hydrolyzing carbapenems have been described in several species (78). A French study showed that approximately 1% to 2% of examined B. fragilis isolates carried a carbapenemase gene, although the gene was expressed in about only half of these (79). Examination of the strains in which expression occurred revealed an IS element upstream of the carbapenemase gene (80). It is thought that a promoter on the IS element is required for carbapenemase expression (80). Chromosomally encoded class A carbapenemases have been described in scattered isolates of Enterobacter and Serratia (81), with plasmid-encoded variants described in K. pneumoniae and P. aeruginosa, but these remain very rare. In Acinetobacter baumannii, carbapenem resistance has been associated with expression of class D enzymes (OXA type), but the exact contribution of these enzymes to clinical resistance in Acinetobacter remains in question (82). ОІ-Lactamase Expression Combined with Membrane Changes It is known that a combination of a permeability deficit plus expression of a ОІ-lactamase with poor hydrolytic activity against carbapenems can lead to clinically important levels of carbapenem resistance. The most well known example of this occurs in P. aeruginosa. In this species, a single outer membrane protein (OMP) functioning as a porin, OMP D2, encoded by the oprD2 gene, is required for transport of imipenem, as well as positively charged amino acids such as lysine (83, 84). At the same time, imipenem is an efficient inducer of expression of the AmpC (class Ia) ОІ-lactamase of P. aeruginosa and other microorganisms (65). Strains that decrease expression of OMP D2 in their outer membranes are resistant to imipenem. It has been shown (Table 90.3) that OMP-mediated resistance requires expression of the AmpC ОІ-lactamase, even though it is an inefficient hydrolyzer of imipenem (84). Since imipenem is an excellent inducer of ОІ-lactamase expression, it is likely that a combination of the two phenomena results in clinical resistance. This same combination of mechanisms has been shown to lead to carbapenem resistance in Enterobacter species and Proteus rettgeri (85, 86, 87). Mutants resistant to carbapenems have been described both in E. cloacae and E. aerogenes, although these mutants are more easily obtained (in the laboratory) in the latter species (85). Clinical isolates of carbapenem-resistant K. pneumoniae expressing a plasmid-mediated AmpC ОІ-lactamase combined with loss of expression of two nonspecific porins have been reported (71). TABLE 90.3. SUSCEPTIBILITY OF MUTANTS OF PSEUDOMONAS AERUGINOSA M2297 TO CARBAPENEMS IN RELATION TO THEIR EXPRESSION OF CHROMOSOMAL ОІ-LACTAMASE AND D2 PORIN An emerging area of interest is the impact of efflux pump expression on resistance to ОІ-lactam antibiotics. This phenomenon has been most carefully explored in P. aeruginosa. Several classes of efflux pumps have been described in gram-negative bacteria. A full description of the different pump classes is beyond the scope of this chapter. The reader is referred for more detailed information to several excellent reviews (88, 89, 90). To understand how these pumps can work in concert to promote resistance to ОІ-lactams and other antimicrobial agents, it is worth considering the case of P. aeruginosa and its efflux pumps that fall into the resistance-nodulation-cell division (RND) class. RND pumps are generally tripartite systems composed of a cytoplasmic membrane portion, an outer membrane portion, and a portion that connects the two across the periplasmic space (88). These pumps serve to extrude material from the cytoplasm into the surrounding media, but also appear to be able to efflux material (particularly ОІ-lactam antibiotics) from the periplasm as well. Four RND efflux pumps have been characterized in P. aeruginosa—MexAB-OprM, MexCD-OprJ, MexEF-OprN, and MexXY-OprM (Table 90.4) (91, 92)— and there are undoubtedly several more. These pumps all have broad substrate specificity. MexAB-OprM is constitutively expressed, whereas MexCD-OprJ P.1600 is repressed in most wild-type strains and MexEF-OprN is variably expressed. MexXY-OprM is expressed at low levels, if at all, during normal laboratory growth. MexAB-OprM pumps out a wide variety of ОІ-lactam antibiotics, but cefepime and cefpirome are poor substrates for this pump. Imipenem is not a substrate for any of the pumps. MexCD-OprJ also has broad substrate specificities, but is limited in its ability to pump ОІ-lactams. In contrast to MexAB-OprM, cefepime is a good substrate for this pump (92). There is in general an inverse correlation between expression of MexAB-OprM and MexCD-OprJ, suggesting some form of control over the total quantity of efflux pumps expressed in a cell at a given time (91). However, the levels of expression observed for MexCD-OprJ in strains devoid of MexAB-OprM do not confer resistance to any antibiotics. Overexpression of MexCD-OprJ is required for resistance. MexEF-OprN may efflux meropenem efficiently, but not imipenem. However, expression of the normally repressed MexEF-OprN is associated with decreased expression of outer membrane protein OprD, the porin associated with imipenem entry into the periplasmic space, reductions in which (in association with AmpC expression—see above) are associated with imipenem resistance. Hence, increased expression of MexAB-OprM and derepression MexEF-OprN are associated with almost universal ОІ-lactam resistance, except for modest susceptibility to cefepime. One outbreak of P. aeruginosa strains expressing this combination of pumps involved 67 patients and required cefepime-amikacin combinations for successful treatment (93). TABLE 90.4. RESISTANCE-NODULATION CELL (RND) PUMPS CHARACTERIZED IN PSEUDOMONAS AERUGINOSA AND THEIR SUBSTRATE SPECIFICITIES RND Pump Substrates MexAB-OprM Q, M, T, L, C, novobiocin, ОІ-lactams except imipenem, aminoglycosides under low ionic strength conditions MexCD-OprJ Q, M, T, L, C, novobiocin, penicillins except carbenicillin and sulbenicillin, cephems except ceftazidime, flomoxef, meropenem Mex EF-OprN Chloramphenicol, quinolones, trimethoprim, carbapenems MexXY-OprM Q, M, T, L, C, aminoglycosides, penicillins except carbenicillin and sulbenicillin, cephems except cefsulodin and ceftazidime, meropenem Q,M,T,L,C, quinolones, macrolides, tetracyclines, lincomycin, chloram-phenicol. Thus, a wide variety of mechanisms lead to ОІ-lactam resistance. At least some of these mechanisms could spread by plasmids and transposable elements. The ОІ-lactam class of antibiotics, representing our least toxic and most potent agents, may no longer offer the therapeutic potential it once did. In my view, a replacement for this class will not be available this decade. CYCLIC GLYCOPEPTIDES The cyclic glycopeptides include vancomycin, teicoplanin (not available for clinical use in the U.S.), as well as a number of compounds such as avoparcin, ristocetin, actaplanin, and others that have not been used in human infections (94). These antibiotics are highly active against gram-positive bacteria. Teicoplanin is more active against enterococci, whereas vancomycin tends to be more active against the staphylococci. Molecular weights of cyclic glycopeptides range from 1,200 to 2,000 d. They all have a central-core heptapeptide, of which three amino acids are highly conserved. Some of these amino acids are crucial to the mode of action of this class. Other important glycopeptide components include the chlorine substituents and the sugars (94). Gram-positive bacteria, most commonly enterococci, expressing resistance to the cyclic glycopeptides have now been described throughout the world, and are causes of significant morbidity and mortality in hospitalized patients, particularly in the U.S. (95, 96). The overwhelming majority of vancomycin-resistant enterococci (VRE) are E. faecium that also express resistance to ampicillin, the other major antimicrobial agent used to treat enterococcal infections (4). They are also frequently resistant to fluoroquinolones, macrolides, penicillins, and to high levels of aminoglycosides (97), rendering most therapies inactive. In the past few years, three new agents (quinupristin-dalfopristin, linezolid, daptomycin) have been introduced to treat VRE infections, but neither of these agents is immune to the problem of resistance. The cyclic glycopeptides bind to acyl-D-alanyl:D-alanine at the terminus of the pentapeptide of the peptidoglycan precursor (94). This binding occurs as the precursor is exiting from the cell membrane to the cell wall, at which point the precursor is added on to the growing peptidoglycan by transglycosylase. Glycopeptides prevent cleavage of the terminal D-ala that is required for establishing the peptide cross-link between adjacent peptide chains. Glycopeptide binding of D-Ala:D-Ala is also thought to cause a “steric” inhibition of transglycosylation, because the bulky antibiotic prevents the transglycosylase from interacting with the peptidoglycan. Virtually all bacteria synthesize peptidoglycan terminating in D-Ala:D-Ala. However, since the currently available glycopeptides are larger than the exclusion limits of the porin proteins of gram-negative outer membranes, only gram-positive species are susceptible to clinically achievable concentrations of this class of antibiotics. Enterococcal vancomycin resistance has been attributed to six different genetic clusters (VanA–E, G) (98, 99, 100, 101). A seventh gene cluster conferring vancomycin resistance (VanF) has been described in the biopesticide Paenobacillus popillae, but has not been found elsewhere (102). The vancomycin resistance operons can be broadly separated into two groups: those that synthesize peptidoglycan precursors terminating in D-lactate (vanA, B, D, hereafter referred to as the lactate operons) and those that synthesize precursors terminating in D-serine (vanC, E, G, hereafter referred to as the serine operons). The lactate operons (specifically vanA and vanB) have spread widely throughout the world and are the predominant operons conferring acquired glycopeptide resistance. They are focused primarily in E. faecium. The serine operons are either intrinsic to some minor species of enterococci VanC in Enterococcus casseliflavus, Enterococcus flavescens, and Enterococcus gallinarum or have been described in only very rare isolates of E. faecalis (vanE and G). vanA and vanB have been described in transposable elements (21, 24) and are generally transferable to enterococcal recipients in vitro, whereas neither vanD nor the serine operons have been shown to be transferable. P.1601 P.1602 Structural comparisons of the six different operons are shown in Figure 90.4. Figure 90.4. A: Depiction of lactate vancomycin resistance operons. Individual gene designations are found under the arrows representing the extent and direction of transcription of the open reading frames. Gray represents regulatory genes. The hatched markings represent the dehydrogenase genes, the black the ligase genes. (See text for specific functions of the different proteins.) B: Depiction of lactate vancomycin resistance operons. Individual gene designations are found under the arrows representing the extent and direction of transcription of the open reading frames. Gray represents regulatory genes. The hatched markings represent the serine racemase genes, the black the ligase genes. (See text for specific functions of the different proteins.) Three functions of the different operons are essential to confer resistance to glycopeptides. First, the resistant substrate must be synthesized (Fig. 90.5). The vanH genes of the lactate operons encode a dehydrogenase that converts cellular pyruvate to D-lactate, whereas the vanT genes of the serine operons convert cellular L-serine to D-serine (hatched genes in Fig. 90.4). The second critical function is ligating the resistant substrate to D-alanine, forming the depsipeptide that is linked to precursor UDP-muramyl-tripeptide to form the pentapeptide precursor. The ligase genes carry the designation specific to the different operons, vanA, B, C, D, E, or G (in black in Fig. 90.4). The third essential function is depletion of the cellular pool of normal D-Ala–D-Ala dipeptide, ensuring that the precursors produced are almost exclusively of the resistant variety. In the lactate operons, the vanX gene encodes a dipeptidase that efficiently cleaves D-Ala–D-Ala, thereby ensuring incorporation of D-Ala–D-Lac into the pentapeptide precursors. The vanY gene of the lactate operons encodes a carboxypeptidase that cleaves the terminal D-Ala from normal pentapeptide precursor, depriving it of the bond breaking that provides the energy to make the peptide cross-link. The vanY gene is not essential for resistance, but serves to amplify the level of resistance when it is expressed. The vanC operon encodes an enzyme with both dipeptidase and carboxypeptidase activity (vanXYC). A homologous gene is also found in the VanE serine operon. The vanG operon, however, contains two open reading frames with vanY homology (vanYG1, vanYG2). It has been hypothesized that one or both of these enzymes may also possess dipeptidase activity (101). The vanA operon contains a seventh gene, vanZ, that results in increased levels of teicoplanin resistance by an unknown mechanism (103). The vanB operon contains a seventh gene, designated vanW, whose function is unknown at present (104), but which is not required for resistance. Figure 90.5. Schematic representation of peptidoglycan biosynthesis in glycopeptide-susceptible (A) and glycopeptide-resistant (B) cells. (From Arthur M, Courvalin P. Genetics and mechanisms of glycopeptide resistance in enterococci. Antimicrob Agents Chemother 1993;37:1563–1571.) In all of the operons, expression of resistance is conferred by two-component regulatory systems encoded by the vanS and vanR genes (gray in Fig. 90.4) that are stimulated by the presence of one or more glycopeptides in the milieu (104, 105). vanR regulates the transcription of the polycistronic message that encodes the three proteins essential for vancomycin resistance. Depending on its phosphorylation state, vanR can serve as either a repressor or activator of transcription. The phosphorylation state of vanR is determined by vanS, the transmembrane sensor component of the two-component system. vanA strains are resistant to both vancomycin and teicoplanin, because the presence of both antibiotics induces expression of the vanA operon. vanB strains remain susceptible to teicoplanin because the operon is not induced by the presence of teicoplanin. Teicoplanin is not a viable therapeutic alternative, however, since mutations resulting in either constitutive expression of the operon or sensitivity of vanSB to induction by teicoplanin are frequent enough to lead to the emergence of resistance on therapy (106). Because the van operons can serve as the sole source for depsipeptide used in the formation of cell wall precursors, there occasionally have been observed strains that are dependent on vancomycin for survival (107). These strains generally possess mutations that lead to nonfunctional cellular ligase genes (108). Under normal circumstances, bacterial cells that have undergone null mutations in their ligase genes would not survive. However, if these strains possess one of the two primary vancomycin-resistant operons, they can survive as long as vancomycin is present in the environment. These strains have been dubbed “vancomycin-dependent enterococci.” They depend on the presence of vancomycin as long as the Van genes are expressed inducibly in the presence of the antibiotic. They provide interesting insight into P.1603 the mechanisms of vancomycin resistance but are of little consequence clinically except in terms of detection where growth in the absence of the antibiotic might not be observed. A variant of the vanD operon has recently been described that lacks vanXD and vanYD activity, but synthesizes lactated precursors exclusively because of constitutive expression in the setting of a null mutation in the normal cellular ligase gene (108). Both vanA and vanB operons have been shown to be mobile. The vanA operon is characteristically encoded by a ca. 10-kb Tn3-family transposon designated Tn1546 (21). This transposon has been found on plasmids, and it is presumed that the transfer of conjugative plasmids explains most of the genetic variability observed in vanA clinical isolates. vanB is characteristically encoded in the bacterial chromosome, although rare reports of plasmid-mediated vanB-type resistance have been published (109, 110). Transfer of vanB-type resistance to enterococcal recipients in vitro has been observed, and is usually accompanied by the acquisition of large segments of chromosomal DNA (111). Two transposons or transposon-like vanB elements have been described. Tn1547 is composite transposon whose mobility is conferred by flanking copies of IS256-related IS elements (112). Tn5382 (and its likely identical relative Tn1549) is a 33-kb transposon with similarities to the conjugative transposons seen frequently in many species of gram-positive cocci (24). The contribution of these various transposons to the genetic variability observed in vanB-type enterococci is probably substantial. Soon after the discovery of the vancomycin resistance operons in enterococci, in vitro studies suggested that the vanA operon could be transferred and expressed in S. aureus. Despite this observation, nearly 15 years passed before the first reports, in 2002, of two clinical S. aureus isolates expressing vancomycin resistance (12, 13) (in Michigan and Pennsylvania). In both cases, the vanA operon has been identified in S. aureus. In one instance the vancomycin-resistant S. aureus was isolated from a wound also contaminated with vanA-expressing E. faecalis. Tn1546 was identified in both strains, although on different plasmids. Fortunately, neither intra- nor interhospital spread of either of these microorganisms has been documented. Nevertheless, their discovery has grave implications for our ability to use vancomycin for the treatment of staphylococcal infections into the future. Mutational resistance to vancomycin in S. aureus has been sporadically reported over the past few years. In virtually all cases, these isolates have been isolated from patients (generally dialysis patients) who have been treated with long-term vancomycin therapy. Resistance is associated with enlargement of the staphylococcal cell wall, and the cell wall itself contains large numbers of unlinked precursors, which can potentially serve as targets for vancomycin binding (113, 114). It has been postulated that resistance results from vancomycin being sequestered within the enlarged cell wall (soaked up like a sponge), preventing achievement of adequate concentrations of vancomycin at the cell membrane, where precursors are added to the growing peptidoglycan. It is likely that this mechanism of resistance is favored only in the setting of persistent and significant vancomycin exposure, since spread to other patients has not been documented and reversion to normal (susceptible) phenotype commonly occurs when in vitro selection by vancomycin is removed. Animal data does suggest, however, that despite marginal minimum inhibitory concentrations (MICs) (ca. 8–16 Вg/mL), this type of resistance will result in vancomycin treatment failure (115). Staphylococcal strains with decreased susceptibility to teicoplanin have also been described. Mutational resistance to teicoplanin is very common among S. hemolyticus and S. epidermidis and, with release of teicoplanin for therapy in Europe, has been described in S. aureus as well (116, 117). Some evidence suggests that PBPs may be involved in the expression of resistance, although the exact mechanism in these strains is still unknown (118). It is possible to select mutants of S. hemolyticus and S. aureus resistant to vancomycin, but only after multiple steps (119, 120). Resistant mutants arising during vancomycin therapy of S. hemolyticus infections in the presence of plastic catheters has been reported in humans (117), but these mutants tend to be unstable. The emergence of normally saprophytic microorganisms intrinsically resistant to the glycopeptides (including lactobacilli, leuconostocs, pediococci, and others) as important pathogens has been reviewed (121). These strains predominantly infect immunocompromised patients. The mechanism of glycopeptide resistance is identical to that described for enterococci. They synthesize a peptidoglycan precursor terminating in D-Ala–D-Lac normally (122). For the most part, these microorganisms remain susceptible to the penicillins. AMINOGLYCOSIDES Structure and Mechanism of Action The aminoglycosides are made of three amino sugars in glycosidic linkage (Fig. 90.6). As such, they are polycationic compounds. They are divided into two classes: the streptidine class, of which streptomycin is the only member in clinical use, and the 2-deoxystreptamine class, which includes all other clinically used aminoglycosides. Uptake of aminoglycosides into bacterial cells is via active transport through the cytoplasmic membrane. The intracellular target of all aminoglycosides is the 30S subunit of the ribosome. For streptomycin, only a single ribosomal-binding site exists, whereas for the others, multiple binding sites are available. In gram-negative microorganisms, aminoglycoside uptake probably occurs via a two-stage process in which the cationic antibiotic displaces magnesium ions linking lipid A subunits. This displacement results in disruption of the outer membrane and diffusion of the antibiotic into the periplasmic space. It seems likely that, in addition to its activity at the ribosome, disruption of the cytoplasmic membrane also plays a role in the activity of these agents. Binding to the 30S ribosomal subunit results in extensive translational misreading and synthesis of abnormal proteins, many of which integrate into the membrane, resulting in further disintegration. It is the sum of these effects that is thought to lead to the bactericidal activity of the aminoglycosides. Figure 90.6. Prototypic aminoglycoside showing sites available for modification and modifications that have been shown to occur. Mechanisms of Resistance Simple mutation of genes encoding ribosomal proteins can result in streptomycin resistance, since only a single binding site P.1604 exists for this antibiotic. Ribosomally resistant mutants have been described clinically, primarily in enterococci and mycobacteria. These mutants remain susceptible to the other aminoglycosides. Mutants with altered membrane transport (the so-called small colony-formers) can also be resistant to aminoglycosides. These cells have altered membrane proton motive force and are unable to transport aminoglycosides across the cytoplasmic membrane. Such mutants are less virulent than their wild-type parents (123). The primary mechanism of bacterial resistance to aminoglycosides is enzymatic modification of the antibiotic (124) (Fig. 90.6). Such chemical modifications prevent binding of the aminoglycoside to the ribosome and may also decrease transport. Three major classes of modifying enzymes have been described that depend on the particular modification involved: phosphorylases, adenyl transferases, and acetyl transferases (Table 90.5). Resistance to all aminoglycosides is achievable by a combination of different enzymes. TABLE 90.5. AMINOGLYCOSIDE-MODIFYING ENZYMES Acetyltransferases Phosphotransferases Adenyltransferases AAC(1) APH(2″)-I ANT(2″)-I AAC(2′)-I APH(3′)-I ANT(3″)-I AAC(3)-I APH(3′)-III ANT(4′)-I AAC(3)-II APH(3′)-IV ANT(4′)-II AAC(3)-III APH(3′)-V ANT(6)-I AAC(3)-IV APH(#′)-VI ANT(9)-I AAC(3)-VI APH(3′)-VII AAC(3)-VII APH(3″)-I AAC(3′)-VIII APH(6)-I AAC(3)-IX APH(4)-I AAC(3)-X APH(7″) AAC(6′)-I APH(9) AAC(6′)-II AAC(6′)-APH(2″) AAC(6)-III AAC(6)-IV From Rather PN. Origins of aminoglycoside modifying enzymes. Drug Resist Updates 1998;1:285-291, with permission. The emergence of enzyme-mediated resistance to aminoglycosides in enterococci is a significant clinical problem. Because of their intrinsic tolerance to the bactericidal activity of all cell wall–active agents, effective treatment of serious enterococcal infections requires the synergistically bactericidal combination of a cell wall–active agent and an aminoglycoside. Since the most common genes encoding aminoglycoside resistance in enterococci were derived from the staphylococci, these two genera will be discussed together. Gentamicin resistance in strains of S. aureus and S. epidermidis first appeared in the U.S. and elsewhere in the mid-1970s (125). In 1979, the first case of high-level resistance to gentamicin, which results in resistance to synergistic bactericidal activity in enterococci, was reported (126). Resistance to aminoglycosides has spread widely in both genera since the first reports. High-level resistance to gentamicin in both staphylococci and enterococci results from modification of the antibiotic by enzymatic mechanisms. Resistance is most commonly encoded by the aacA-aphD resistance gene, the product of which is a 6′-acetyltransferase-2′′phosphotransferase (6′-AAC-2′′-APH) bifunctional enzyme, a fusion protein that possesses both of the above enzymatic activities (127). The 6′-AAC component of the bifunctional enzyme confers resistance to amikacin, kanamycin, and tobramycin, whereas the 2′′-APH component is primarily responsible for resistance to gentamicin and netilmicin. All strains that possess this gene are resistant to all of the above-mentioned aminoglycosides. Streptomycin, which is inactivated by a separate enzyme, is the single clinically available aminoglycoside not inactivated by the bifunctional enzyme. The nucleotide sequences of the genes responsible for the production of the bifunctional enzyme are identical in S. aureus and E. faecalis, and probably in E. faecium, S. epidermidis, and S. agalactiae as well (127, 128, 129). These genes are often integrated into conjugative plasmids in both staphylococci and enterococci. In addition, the bifunctional enzyme gene has been found integrated into transposons in S. aureus (Tn4001), S. epidermidis (Tn4031), and E. faecalis (Tn5281) (130, 131, 132). Nucleotide sequence analysis of the region adjacent to the enterococcal gene and structural analysis of the enterococcal transposable element reveal extensive similarities with Tn4001 from S. aureus. Two additional genes that confer resistance to aminoglycosides in enterococci have been described in the past decade (133). Unlike the bifunctional enzyme, these phosphotransferases do not confer resistance to a wide range of aminoglycosides. In addition, they may confer only relatively low levels of resistance (256 Вg/mL) when tested by standard techniques, and therefore may be missed in screening assays designed to detect the more common enzymes. Despite these lower levels of resistance, they do confer a resistance to cell wall–active agent-aminoglycoside synergism, so they may prove to be important for the treatment of endocarditis. The overall prevalence of these enzymes is relatively low at present but it bears watching, and physicians are well advised to consider the possibility that such an enzyme is present when treating serious enterococcal infections. P.1605 High-level gentamicin resistance in enterococcal isolates has spread rapidly in some hospitals, with one center reporting 55% of nosocomial enterococcal isolates resistant to gentamicin (10). Gentamicin-resistant enterococci appear to be transmitted in the hospital setting on the hands of caregivers. Measures undertaken to limit such transmission have proven effective in containing outbreaks of infection and colonization with these microorganisms (134). A growing body of evidence suggests that serious infection with these strains is associated with a worse prognosis than is associated with infections caused by susceptible isolates (135, 136, 137). Episodes of failure (resulting in death or requiring surgical intervention for cure) in the treatment of enterococcal endocarditis caused by gentamicin-resistant strains have been reported (137, 138). Fortunately, most enterococcal infections can be successfully treated with a single agent. For more serious infections, it is essential to test all enterococcal isolates for high-level resistance to both gentamicin and streptomycin. Depending on the center, anywhere from 0% to 45% of enterococcal strains exhibiting high-level gentamicin resistance are reported to remain susceptible to streptomycin (136, 139). Combinations of cell wall–active agents and streptomycin should be effective in the treatment of strains exhibiting high-level gentamicin resistance but lacking high-level resistance to streptomycin, and vice versa (138, 140). At present, there is no reliable bactericidal combination of antibiotics against strains exhibiting high-level resistance to both gentamicin and streptomycin. In gram-negative microorganisms, aminoglycoside-modifying enzymes are the most important mechanisms of resistance. In general, genes encoding such enzymes are carried on plasmids or transposons and are expressed constitutively. However, in the case of S. marcescens and Providencia stuartii, aminoglycoside acetyltransferases are normally encoded by chromosomal genes but are not well expressed (141, 142). It appears that, in these species, the chromosomally encoded acetyltransferases represent intrinsic housekeeping genes that are responsible for acetylating peptidoglycan (143). Aminoglycosides bear structural resemblance to peptidoglycan, and are acetylated as well. Normally these enzymes are produced in amounts sufficient to acetylate peptidoglycan, but not to result in resistance. Mutants that express these enzymes at high levels can be easily selected, and probably account for many of the aminoglycoside-resistant strains of these species. Gram-negative bacteria also employ efflux pumps to assist with aminoglycoside resistance. In P. aeruginosa, the MexXY-OprM system is most commonly implicated in aminoglycoside efflux (144), but more recent data also implicated MexAB-OprM and an analog of the E. coli small multidrug resistance (SMR)-type pump emrE (emrEPae) (145). The MexAB-OprM pump effluxes aminoglycosides in vitro, but only when tested in low ionic strength media. An RND pump has also been recently implicated in aminoglycoside resistance in Acinetobacter baumannii (146). The area of efflux pump-mediated resistance is only beginning to be explored, and there will no doubt be significant discoveries made in this area over the next decade. Although many clinicians retreat from aminoglycoside use in the therapy for gram-negative infections, there are accumulating data that, at least for a subset of patients, the combination of aminoglycoside with ОІ-lactams is superior to either agent alone, or even to other combinations (68, 147). Furthermore, it is unlikely that this beneficial effect is due to the suppression of emerging ОІ-lactam–resistant mutants (68). In addition, the popularization of once-daily aminoglycoside therapy may lead to more aminoglycoside use in the future. Thus, aminoglycoside resistance in gram-negative species may ultimately be more important than is currently thought. RESISTANCE TO THE FLUOROQUINOLONES Structure and Mechanism of Action The quinolone class of antibiotics can be historically traced to nalidixic acid. These antibiotics are potent inhibitors of cellular topoisomerases, enzymes required for winding and unwinding supercoiled, double-stranded DNA (148). Quinolone antibiotics act by inhibiting DNA synthesis. Their targets are two type 2 topoisomerases, DNA gyrase and topoisomerase IV. These two enzymes both exist as tetramers composed of different subunits (GyrA and GyrB of DNA gyrase; ParC and ParE of topoisomerase IV). DNA gyrase maintains negative supercoiling of DNA, whereas topoisomerase IV separates interlocked DNA strands formed during replication, facilitating segregation into daughter cells. Fluoroquinolones bind to the topoisomerase-DNA complexes and disrupt cellular processes involving DNA (replication fork, transcription of RNA, DNA helicase) (149, 150, 151). The end result is cellular death by unclear mechanisms. Fluoroquinolone affinity for the two targets varies with the compound, explaining to some extent differing potencies. The enzyme for which a particular fluoroquinolone has the greatest affinity is referred to as the primary target (152, 153, 154). It is generally but not universally true that DNA gyrase is the primary target of fluoroquinolones in gram-negative bacteria, whereas topoisomerase IV is the primary target in gram-positive bacteria. Alterations in Target Enzymes The most common mechanism of fluoroquinolone resistance is point mutations of the topoisomerase genes resulting in structural alterations in the topoisomerase enzymes. In gyrA and parC, resistance-associated mutations are often localized to a region in the enzyme that contains the active site tyrosine covalently linked to the broken DNA strand. This 130 base pair (bp) region of gyrA has been referred to as the quinolone-resistance-determining region (QRDR) (155). X-ray crystallographic studies of a fragment of the gyrA enzyme suggest that QRDR mutations are clustered in three dimensions, supporting the hypothesis that this region constitutes a part of the quinolone binding site (156). Frequent sites for resistance-associated mutations are serine 83 and aspartate 87 of DNA gyrase and serine 79 and aspartate 83 of parC (157). The level of resistance conferred by a point mutation in the primary target enzyme depends on the change of enzyme affinity created by the mutation and the affinity of the specific fluoroquinolone for the secondary target. As such, fluoroquinolones exhibiting strong affinity for both target enzymes may be less likely to promote the emergence of resistant strains in the clinical setting, since the activity against the secondary target may be P.1606 enough to inhibit the bacterium even in the presence of primary target mutation. Consistent with this hypothesis, fluoroquinolone-species combinations for which single mutations result in significantly higher MICs (such as ciprofloxacin and S. aureus or P. aeruginosa) have readily selected out resistant mutants in the clinical setting (158). Most highly resistant strains exhibit more than one mutation in both the gyrA and parC enzymes. It is noteworthy in this context that fluoroquinolone resistance conferred by enzyme mutations is to some degree a class resistance in which the activity of all fluoroquinolones is impacted. Thus, although single point mutations conferring resistance to one fluoroquinolone may not yield MICs conferring clinically significant levels of resistance for another, the MICs for the all fluoroquinolone will inevitably be increased. These preexisting mutations may then serve as the template to select additional mutations that result in more broad-spectrum fluoroquinolone resistance. Some experts suggest that this phenomenon should prompt clinicians always to use the most potent fluoroquinolone when treating infections, to prevent the emergence of resistance. Some degree of skepticism about such recommendations is warranted, since potency varies with the microorganism (moxifloxacin may be more potent against S. pneumoniae than ciprofloxacin, but the reverse is true for P. aeruginosa) and fluoroquinolone concentrations achievable in many areas of the body (such as the gastrointestinal tract) may not approximate those needed to prevent the emergence of resistance. Such recommendations, therefore, should be tested in controlled clinical trials before they are widely adopted. Mutations in gyrB and parE are less common than in gyrA and parC and cluster in the midportion of the subunit (159). The true impact of these mutations on expression of resistance remains to be determined. Resistance Due to Decreased Intracellular Accumulation Fluoroquinolones penetrate the outer membrane of gram-negative bacteria through porins, and so the absence of specific porins may theoretically impact the susceptibility. However, diffusion through outer and cytoplasmic membranes is generally sufficient to retain activity against strains solely lacking porins (160). More important in reducing intracellular accumulation of fluoroquinolones is the expression of multidrug resistance pumps (157). All of the pumps described above for P. aeruginosa have been shown to efflux fluoroquinolone antimicrobial agents (91, 92). By themselves, pumps generally confer only a low level of resistance to fluoroquinolones. However, their expression may amplify the level of resistance conferred by point mutations within the topoisomerase genes. By so doing, they may increase the risk that a given fluoroquinolone will select out resistant mutants through single point mutations. A transferable, plasmid-mediated form of resistance to fluoroquinolones has been described in a strain of K. pneumoniae (161). The gene conferring this resistance has been designated qnr, and its mechanism discerned to be protection of the DNA gyrase from interaction with the fluoroquinolone (162). The extent to which qnr-like genes will become prevalent in the population remains unknown, but recent data suggest that at present its prevalence in the U.S. is very low (163). Resistance to Newer Antimicrobial Agents The emergence and spread of multiresistant enterococci in the past decade, accompanied by the inexorable increase in the prevalence of MRSA, has amplified the importance of finding new agents with clinically important activity against resistant gram-positive cocci. Two such agents have been licensed in the past 5 years. Quinupristin-dalfopristin is a combination of two pristinamycins (one of the streptogramin A class, the other a streptogramin B) that have synergistic activity against E. faecium (although they are ineffective against E. faecalis) and S. aureus. The overall use of this combination has been limited by considerations of cost and toxicities, and by the need to administer through a central venous catheter. Despite its limited use, two forms of resistance have already been noted in E. faecium. The first is a low-level resistance whose mechanism remains to be fully defined, but which may involve activation of an efflux pump. Data from a recent clinical study reported that 21% of E. faecium isolated exhibited such low-level resistance (95). This type of resistance has not been shown to be transferable, and its impact on therapy remains to be determined. High-level resistance to these mixtures can result from resistance to streptogramin A alone and was first described in staphylococci conferred by genes encoding streptogramin A acetyltransferases [vat(A), vat(B), and vat(C)] or adenosine triphosphate (ATP)-binding efflux genes [vga(A), vga(B)]. Two acetyltransferase genes have now been described that confer resistance to quinupristin-dalfopristin in E. faecium—vat(D) [previously sat(A)] and vat(E) [previously sat(G)]. In most cases, these resistance genes are found along with an erm resistance gene (164), suggesting that resistance to both streptogramin A and B may be necessary to confer clinically significant levels of resistance to quinupristin-dalfopristin in E. faecium. These genes have been found on transferable plasmids, suggesting that the potential for spread is significant. Linezolid is the first licensed member of the oxazolidone class of antibiotics. It is active against most multiresistant gram-positive cocci including multiresistant enterococci and S. aureus. Linezolid acts by binding to the conglomeration of ribosomes, messenger RNB (mRNA), and transfer RNA (tRNA) known as the initiation complex, thereby inhibiting protein synthesis. Resistance to linezolid has been associated with point mutations in the 23S ribosomal RNA subunit (165). The most common mutation found in resistant isolates has been a Gв†’U change at position 2576 (E. coli numbering scheme). The degree of resistance seen in enterococci is related to the percentage of ribosomal RNA (rRNA) genes that have this mutation (166). This type of resistance has not been transferable in any of the cases examined to date. However, the known transferability of enterococci themselves within the healthcare setting creates concern that these strains could become prevalent. One outbreak of such strains in a liver transplant unit has already been reported (167). P.1607 CONCLUSION Despite our best efforts, the elusive promise of the “perfect” antibiotic has not been realized. Experience with the use of antibiotics in the clinical setting has taught us that resistance often emerges soon after the clinical introduction of any antibiotic, and in some cases these resistance determinants spread rapidly once they are present in human pathogens. Resistance may be promoted by the excessive and injudicious use of antimicrobial agents, as well as by poor infection control practices employed in the hospital, day-care centers, and the home. Guidelines for the prevention of resistance in hospitals have been issued jointly by the Society for Healthcare Epidemiology of America and the Infectious Diseases Society of America (168). The guidelines suggest a number of strategies including some aimed at testing the hypotheses and proposals contained within the document. We hope that these suggestions will be implemented so that optimal programs based on data can be introduced. 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A building ventilation system is expected to supply air at a comfortable temperature and humidity level (1, 2). In the hospital setting, heating, ventilation, and air conditioning (HVAC) systems must often provide specially conditioned air to protect the health of patients and staff. Certain patients are particularly vulnerable to infection from airborne pathogens (3). Others, such as tuberculosis patients, are potential sources of airborne infection, which may put those around them at risk. To design a proper hospital ventilation system, one must be familiar with both the physical and biologic characteristics of airborne agents causing nosocomial infections. Knowledge of ventilation strategies and equipment used to reduce the potential for airborne transmission of disease requires understanding of airborne particle management for contamination control (4). The science of aerobiology began with Louis Pasteur's discoveries in the middle nineteenth century. By this time, investigators had made great strides in characterizing airborne flora and fauna and in developing methods for accurate quantitative sampling of these populations. During the 1930s, William Wells published on the infectious capacity of droplets and droplet nuclei. He also studied the air-sterilizing properties of ultraviolet (UV) light. By the 1960s, investigators were reporting on the airborne transmission of a variety of infections, including tuberculosis, influenza, smallpox, and measles. From particle science and fluid dynamics has evolved the study of bioaerosols, which quantitatively describes the generation and dispersal mechanisms that dictate the behavior of airborne microorganisms (5). By applying an understanding of these biologic and physical principles, the hospital can provide a ventilation system that can help protect against the spread of nosocomial or occupationally acquired infection. BIOAEROSOLS AND INFECTION For an object to remain airborne, it must be small enough so that the viscosity of the air impedes its fall in response to gravity. Lewis Stokes (6) developed an equation that predicts the falling velocity of a particle as a function of its diameter. Stokes's law for determining the sedimentation velocity (Vs) of particles from 1 to 100 Вm in diameter is as follows: where Пѓ is the density of the particle, g is the acceleration of gravity, ПЃ is the density of the medium, r is the radius of the particle, and В is the viscosity of the medium. Gregory (6) published a table of experimentally observed falling velocities for a number of microorganisms. It can be readily observed that many particles ranging in size from 1 to 5 Вm have falling velocities in still air on the order of 1 yard an hour. Many spores, such as those of Aspergillus fumigatus, have roughened surfaces that tend to further enhance their buoyancy. Such particles can stay airborne almost indefinitely and can ride on air currents for thousands of miles from their point of origin (Fig. 89.1). Figure 89.1. Observed terminal velocities of fall of spores and pollen related to diameter. Falling velocity of selected spores in centimeters per second. (From Gregory PH. The microbiology of the atmosphere, 2nd ed. New York: John Wiley & Sons, 1973:21, with permission.) It is important to realize that, if such small particles were entrained in a patient's respiratory airstream, they are of the size most likely to elude the cilial and mucosal defenses of the upper respiratory tract and to deposit in the alveoli of the deep lung (Fig. 89.2). Since the early 1970s, investigators have enhanced the understanding of the respiratory fate of small particles as a function of their Stokes diameter. Figure 89.2. Upper and lower respiratory tract (URT and LRT) deposition of idealized spherical particles as a function of diameter. (From Rhame FS, Mazzarella M, Streifel AJ, et al. Evaluation of commercial air filters for fungal spore removal efficiency. Third International Conference on Nosocomial Infections, Atlanta, 1990, with permission.) Quantitative information about particles is as reliable as the measuring instrumentation. By knowing the airborne spore concentration in a given air body and the tidal volume of the lung, one can estimate the probability of inhaling a certain quantity of pathogenic material. Riley and Nardell (7) used the concept of infectious dose in the form of quanta to predict the probability of infection from the release of infectious particles. Using ventilation, one can achieve protection, to a degree, before reaching a point of diminishing returns (8) for infection control, especially for agents such as Mycobacterium tuberculosis. Reliable assessment of biologic risks from airborne pathogens is difficult because of the variables that are intrinsic to living systems. Two Aspergillus spores or influenza virus particles may have widely differing potentials for causing infection, depending on such factors as viability of the spores or particles and the P.1578 health status of the person inhaling them. To determine control strategies for such agents, it is first necessary to estimate what constitutes an infective dose and then to determine what sort of ventilation control system will reduce concentrations of the suspected pathogen to a safe or noninfective level (9). GENERAL VENTILATION PRINCIPLES Although air is a gaseous mixture containing nitrogen, oxygen, carbon dioxide, and a number of trace elements, it behaves in accordance with the principles of fluid dynamics. In descriptions of ventilation systems, air is treated as though it were a liquid flowing through the system. Air moves in response to pressure. For liquids, the most common source of pressure is gravity. For gases, the most common source of pressure is temperature. The global system of air movement is powered by the rays of the sun. In a building HVAC system, pressure is provided by fans that push or pull air through the building. The most basic rule of airflow in a duct system is that air in must equal air out (10). For any two points in a closed duct, A1V1 = A2V2, where A1 is the cross-sectional area (measured in square feet) and V1 is the air velocity (in feet per minute). A1V1 gives the airflow in cubic feet per minute (cfm). This equation indicates that if the ducts contract (reducing A), air speed, V, must increase proportionally to maintain the same cubic feet per minute flow rate. The basic rule of air pressure is TP = VP - SP, where TP is the total pressure in the system, VP is the velocity pressure, and SP is the static pressure. Velocity pressure is measured in the direction of airflow and is directly proportional to V, the speed of the moving air. Velocity pressure is always positive. Static pressure is the pressure a body of air exerts on its container, and it can be measured in all directions. Static pressure may be either positive or negative. It is pressure that tends to either burst (positive pressure) or collapse (negative pressure) the duct. If a body of air increases in speed, the velocity pressure increases whereas the static pressure drops. TP, the total pressure, may be either positive or negative and is the sum of the static and velocity pressure. As a body of air moves through a duct system in response to pressure generated by a fan, the total pressure in the system decreases because of frictional losses between the moving air body and the walls of its container, the duct system. This concept is illustrated by a third equation, TP1 = TP2 - HL, which tells that, for a body of air moving from point 1 to point 2, the total pressures at the two points differ by the frictional losses (HL) caused by the intervening run of duct. These three rules provide the conceptual framework within which ventilation systems are designed. In a simple recirculating model, the fan creates sufficient positive pressure to force air through the supply duct work and sufficient negative pressure to draw the air out of the rooms into the return duct work and back to the fan, completing the circuit. The pressure generated by the fan must be sufficient to overcome the energy losses created by friction between the moving air and the duct system through which it travels. The duct work blows air into the various rooms through supply openings. The air circulates in the room and then moves toward return openings that draw air back into the return duct system with negative pressure (suction). The supply and return openings in the room illustrate an important difference between positive and negative pressure ventilation. An individual with healthy lungs can easily blow out a candle at arm's length. The same healthy lungs could not generate enough negative pressure, or suction, to cause the flame to even flicker (11). The supply duct is comparable with blowing out the candle, whereas the exhaust is attempting to suck it out. We refer to the strong directional flow of positively pressured supply air as “throw,” whereas the negatively pressured exhaust duct has a “capture velocity” (Fig. 89.3). The control of such a ventilation system is facilitated by a sealed room. A seal on the room allows air to enter and escape only through the ducted P.1579 openings. Such measures help to maintain consistent control of the ventilation (12). Figure 89.3. Basic difference between flow and pressure openings. HOSPITAL VENTILATION SYSTEMS In designing a HVAC system for any occupied building, one must properly size ducts and fans to provide the proper air pressures and duct velocities to meet the ventilation requirements of the entire building. Properly sized heating and cooling equipment and noise reduction enter into the total calculations, as does some sort of filtration or air cleaning system. As air recirculates in a building, it builds up an increasing load of gaseous contaminants that are not readily removed by filtration. It is necessary to exhaust a certain percentage of this stale air and replace it with fresh outdoor air to ensure occupant health and comfort (13). A wide variety of systems have been used to meet these criteria. I consider a few of the more common types with an eye toward the needs of the hospital environment. Central Air Conditioning System This system brings in fresh outdoor air and mixes it with recirculated air. This air mixture is filtered and conditioned for temperature and humidity according to institutional requirements and then distributed to all building locations. This system is favored for its low cost and simplicity. In a large hospital, the major drawback of centrally conditioned air is the difficulty in adapting it to the specific requirements of local areas, which may have differing heating and cooling needs. This is a particular problem in cold climates in which rooms along the exterior shell require warmer air than rooms in the central core. Large central supply ducts, which reduce noise by slowing airflow, require large amounts of space. Efforts to create local or zone conditions with additional equipment, such as extra heating and cooling coils or booster fans, rapidly increase costs and are often only partially effective. Dual Duct System This system has a central system that separately produces two air streams, one hot and the other cold, which are then parallel-ducted throughout the building. Each room is provided with a mixing box in which the two air streams are blended. This allows individual thermostats and volume controls for each room. Although more expensive and difficult to install, this system can provide a number of microclimates without much add-on equipment. The principal drawbacks are the degree of care required in installing the system and the sound baffling required to reduce the noise created by faster airflows within the smaller duct work. Other variations in the air-handling system may be unique to a regional climate condition that design engineers have considered in the ventilation specifications. This may be a factor for the considerations for humidification or dehumidification. The control of water in the air-handling system is paramount for controlling potential allergens and pathogens associated with growth of microorganisms on fibrous insulation (14, 15). The air-handling system variation can depend considerably on design for the climate. All designs require careful maintenance and operational considerations for infection control. For example, a local fan coil system has often been used in hospital areas requiring supplemental cooling. Such climate control is often provided with local systems that recirculate ambient air and provide dehumidification and cooling. Such systems, although engineered for temperature control, do not accommodate air purification control. The drain pans, if not properly maintained, become reservoirs for local fungal contamination (16). Air conditioners may also be reservoirs for fungal growth or accumulation (17, 18). Such systems should be discouraged for areas in which immunocompromised patients are hospitalized. Recent outbreak investigations have demonstrated prolific growth on cold ducted systems either on filters or associated with mixing boxes. Filtration Hospital HVAC systems are often required to perform additional tasks related to the prevention of nosocomial infections. By appropriate use of air-filtration technology, a hospital air-handling system can deliver air that is virtually particle free to areas where such a level of protection is needed. The problem presented by such a rigorous filtration system is the energy cost involved. Most filters scrub the air by trapping particles in dense pleated media. Dense filters impede the flow of air and cause a loss of system pressure. To maintain effective air velocities in the duct work, a more powerful fan must be installed to overcome this pressure drop across the filter. Filters are rated by their percentage of efficiency. A number of different test methods are used to rate air filters (19, 20). Most common are the dioctyl phthalate (DOP) and dust spot tests. The DOP test challenges an air filter with an aerosol 0.3 Вm in diameter. A light-scattering instrument downstream measures the penetration of the filter by these particles. A filter that can arrest 99.97% of the DOP particles is referred to as a high-efficiency particulate air (HEPA) filter. This method actually counts particles as a measurement of efficiency. The dust spot test is used to rate less rigorous filters. This test uses atmospheric air or a defined dust as the challenge. Air upstream and downstream from the tested filter is drawn through filter paper. The samples are then compared for opacity using a photometer. Although not quantitative in evaluating P.1580 particle reduction, this test measures the ability of a filter to reduce the dirt load of an air stream. Kuehn (21) and Rhame et al. (22) have shown that dust spot methods can measure high-efficiency removal of particles. The most effective hospital filtration system has been evaluated for air cleaning. Outdoor air is initially filtered through 20% to 40% efficient media, mixed with recirculating air, and sent through a 90% dust spot efficient filter. These 90% filters have been demonstrated to provide nearly 100% efficiency in removing particles 1 to 5 mm in diameter with a lower pressure drop than when the 99.97% HEPA filters are used. Modern filters designed with larger surface areas can provide high filter efficiency while maintaining relatively low pressure drops compared with previous versions of the HEPA filter. Distributing such clean air throughout the system provides an additional layer of safety to all occupants at risk for airborne pathogens. Then, where required, rooms or zones can be HEPA-filtered for a higher degree of protection. Modern filtration technology is creating low-pressure drop filters resulting from fiber electrostatic qualities and increased surface area of the filter. Although reduced resistance pressure while maintaining high-filter efficiency is beneficial for cost savings, careful consideration for proven long-term efficiency is necessary to prevent problems (23). High-efficiency filter innovation certainly helps provide sufficient air volume to assist in maintaining essential air quality parameters in hospitals, which often become deficient in air volume delivery and exhaust as the building ages. Such systems reduce risks created by opening and shutting doors and from transporting vulnerable patients for procedures that cannot be performed in specially protected areas. Filtration continues to dominate priorities for air quality (24, 25) in prevention of aspergillosis. The combination of appropriate ventilation parameters (filtration, air exchanges, and pressure) helps in the control of the many sources of opportunistic filamentous fungal infections plaguing the immunocompromised host (26). AREAS REQUIRING SPECIAL VENTILATION Certain areas in the hospital have special ventilation systems as described in the HVAC handbook (1) and American Institute of Architects guidelines for hospital construction (2). Air systems have been designed to meet these specific needs, most commonly operating rooms, positive-pressure protective environments, negative-pressure isolation units, and local air control flow life islands (Table 89.1). Each of these situations has specific ventilation requirements related to prevention of nosocomial infection or occupational exposure to airborne infectious diseases or medicated aerosols or gases. All operate on the underlying principle that clean air should move from less contaminated to more contaminated areas (clean to dirty airflow). To more clearly illustrate the principles involved, I discuss a specific patient, pathogen, or procedure for each type of situation. TABLE 89.1. SUMMARY OF SPECIAL-VENTILATION HOSPITAL AREAS Protective Environments Operating Room Surgery is by nature a process requiring invasive procedures that expose host tissues to the outside environment, creating the potential for exposure to external agents, such as bacteria and fungi. Therefore, in the operating room, the surgical site and instrument table should be considered the cleanest area, and infection control efforts should be directed toward providing protection through appropriate ventilation control. Surgical site infection is a well-documented surgical complication (27). Aseptic technique and prophylactic antibiotics provide the first line of defense, but it has been shown that removing bacteria and fungi from operating room air helps to minimize infection (28, 29). Microorganisms shed by humans are the most common airborne agents in a correctly designed operating room with appropriate air filtration (30). Large volumes of air filtered through high-efficiency filters should be provided from panels in the operating room ceiling over the surgical site. The downward force of air from the ceiling supply diffuser provides a focused ventilated area around the surgical site that is constantly washed by a high-volume flow of clean air. Such airflow moves particles away from the operating table toward the air returns at the margins of the room. It is important that this displacement airflow of filtered air is delivered in such a manner that infectious particles shed by the operating team are swept away toward the return ducts and not trapped and recirculated within the vicinity of the procedure. The more objects that interrupt the airflow pattern, the greater the turbulence. Special clean room laminar flow ventilation with HEPA filtration has been used in orthopedic cases to prevent the consequences of surgical site infections. A vertical flow system designed to provide a downward flow of air over the surgical site actually increases the air exchanges in the cleanest zone (31). Air delivery from a horizontal direction does not provide an extra benefit, because personnel and equipment in the way of the directed airflow cause turbulence and potential trajectory of problematic particles toward the surgical site. Vertical flow is preferred over horizontal airflow for space management and infection control considerations (32). Memarzadeh and Manning (33) performed computational fluid dynamic studies which reinforced the empirical findings of Lidwell (32) that a vertical flow with velocity from 30 to 35 linear feet per minute (lfpm) (0.15 to 0.18 m/second) could be achieved at the surgical site. If air supply can provide a laminar flow regimen albeit at a lower velocity than official definition of laminar flow of 90 lfpm (0.45 m/second), control of the shed particles over of the surgical site is realistic. Pressure management in the protective operating room environment is designated by a positive airflow out of the cleanest area of the operating room suites. This designation does not give guidance for what is necessary to provide that pressurization. Murray et al. (12) have suggested that a differential air volume (supply versus exhaust or return) exceeding 10% to 15% provides the required airflow. This concept works best in a high volume environment like an operating room or in bone marrow transplant rooms, which require higher airflow volumes. Such suggestions have not been validated. Consistent management of pressure is a problem when windows are operable or doors are left open. Using an anteroom or door closure is an essential component for room pressure management. Operating rooms have multiple doors, and, if any of those doors are open, the pressure differential is eliminated until the door is closed. Proce P.1581 dural practice for operating rooms should include closed doors, except for egress, while the surgical site is open. Investigations have shown value in properly clothing the operating room team for maximum contamination control. The surgical team is a potential reservoir of infection. The average person sheds approximately 107 particles of sloughed skin per day (34, 35). During an hour-long surgical procedure, each individual in the operating theater may shed 106 particles. Each one of these particles may be carrying bacteria that can infect a surgical site. However, in the properly ventilated operating room, such shedding should not pose an infectious risk to patients. For operative procedures involving insertion of a prosthetic device and for which ultraclean air may be desired, shedding can be greatly reduced by providing surgical personnel with negatively pressurized evacuated gowns. Opportunistic environmental microbes such as Clostridium perfringens or Aspergillus spores should be minimized in an operating room setting. These soil microorganisms are readily filtered from incoming air if filters are installed and maintained properly. Such microorganisms would be expected in air supply systems that have leaks or tears in the filters. A lack of maintenance also is a problem, because it allows a reservoir of microbial growth in the air-delivery system. Such inadequate maintenance or installation must be avoided in the critical surgical areas. Shed microbes from human attendants must be controlled with the directed airflow and barrier protection. Tunevall and Jorbeck (36) raised the issue that masks do not affect the presence of microbes in a surgical setting. The range of microbial recovery from air sampling suggests that the use of barriers prevents the inadvertent shedding of microbes from exposed areas such as the mouth or hair. Barriers have also been shown to prevent contamination of drapes and the surgical site. With aseptic technique and appropriate ventilation, the exposed skin from both the patient and attendants becomes an important source for microbial exposure in the surgical setting (37). Unclean floors from track dirt and accumulated debris could become an internal source for C. perfringens or other soil microorganisms (38) if disturbed. Human source microbes can be controlled with aseptic technique (39) and barrier protection (40). A forced air ventilation system enhances the cleanliness of the critical surgery area. The ventilation system is essential for protecting the surgical site using particle displacement dynamics of properly directed purified air movement. The patient is also a potential source for infecting the personnel in the operating room setting. The generation of aerosols during the use of cautery and lasers is a matter of concern. Information on the transmission of infectious agents by these procedures is minimal; however, scavenging devices are being used to minimize the presence of obnoxious odors or aerosols in the operating room setting. For example, such local exhaust and filtration systems can be used to capture problematic aerosols generated during the removal of extrapulmonary tuberculosis lesions. Positive-pressure Room (Protective Environments) Oncology and Solid Organ Transplant Patient Modern medical technology has provided methods for transplanting immunologically dissimilar tissue between donor and recipient. The immunosuppressive treatment necessary to prevent rejection of the transplanted organ or tissue puts the host at risk for opportunistic infections. Environmental pathogens causing legionellosis or aspergillosis are common (3, 41, 42) and must be controlled in a critical hospital setting. These environmental microorganisms pose little threat to the healthy individual protected by normal humoral and cellular immune defenses. A. fumigatus is a common soil fungus. Its spores range in diameter from 2 to 3.5 Вm and are commonly recovered from outdoor air samples. This airborne fungus is cosmopolitan and is commonly recovered when using a volumetric air sampler. This thermotolerant fungus poses a particular risk as a nosocomial pathogen because of its ability to reach the alveoli in the lung and its ability to thrive at 37ВC. On inhalation by the granulocytopenic patient, these spores can cause a form of pneumonia that is difficult to diagnose and treat. Peterson et al. (43) noted that 17 of 19 patients with aspergillosis died in a series of 60 patients. Opportunistic filamentous fungal infections seem to be less responsive to conventional antibiotic therapy. Providing spore-free air through filtration and ventilation and local activity control is the best method for preventing infections transmitted by fungal spores (44). Because some patients remain immunocompromised for up to several months, it is also necessary to minimize airborne environmental contamination by microbes in the environment of convalescent transplantation and oncology patients. The basic ventilation approach in such facilities is to provide P.1582 positive-pressure ventilation wherein the amount of HEPA-filtered supply air exceeds the amount of air exhausted by at least 10%. The offset should be about 125 cfm between the supply and exhaust/return to provide a substantial difference for ensuring consistent pressure differential in the special ventilation rooms. This difference should be able to establish a pressure differential greater than 0.01 inches water gauge (2.5 Pa). By delivering air at a rate of between six and ten air changes per hour, depending on heating and cooling requirements, and by using supply and return air that ensures thorough mixing, the room can be kept relatively spore-free (45). Supply air diffusers should be located in the ceiling and positioned to throw air down far enough into the room to ensure particle displacement and mixing. In the protected ventilation environment, the filtered air should flow from the vulnerable patient toward the corridor. Such clean to dirty airflow provides air movement that should prevent inhalation of common airborne fungal spores by the patient. Bone Marrow Transplantation Unit Simple positive pressure ventilation may not provide sufficient protection for the extremely vulnerable patient. Patients requiring bone marrow transplants are often housed in laminar air flow (LAF) rooms (41). Such rooms are designed with one entire wall of HEPA filters. Fans blow air through these filters at high velocity [about 100 to 150 lfpm (46, 47)] and out through high-capacity return ducts located on the opposite wall. Although the term laminar flow is not an accurate description of the fluid dynamics of the airflow under such conditions, the effect is that smoke particles injected into the LAF air stream are swept straight across the room, parallel to the floor, and out through the return. It is as though a piston of clean air is being pushed across the room, driving any contaminants out through the return ducts. To enhance patient protection, all caregivers should work downstream from the patient so as not to impede the protective airflow across the bed. Such rooms provide more than 100 air changes per hour. The high velocity of the airflow can create uncomfortable drafts and excess noise. Housing patients in such an environment is an extreme measure and can be problematic during long periods of convalescence. Because of high cost and limited availability, these LAF systems are difficult to provide for all immunosuppressed patients. Therefore, less drastic ventilation control procedures are often recommended (48, 49) (Table 89.2). TABLE 89.2. COMPONENTS OF A PROTECTED ENVIRONMENT Sealed room (windows and utility connections) Increased room air changes (>12) Highly filtered air (>95% efficient @ 0.3-Вm particles) Positive pressure rooms (>10% or >125 cfm) supply over exhaust/return air volume) Directed airflow (airflow from the “clean” patient to the “dirty” patient) Leakage total for room at 0.5 ft2 Procedural practice modification Self-closing doors The problem most frequently associated with contaminated hospital air is construction activity (50). Control of aerosol generation, airflow, filtration, barrier penetration, and traffic requires careful monitoring and supervision to maintain specially ventilated areas. Air filtration and increased room air changes help to prevent infection in areas adjacent to construction activity (51, 52). Patients must be continuously confined in such rooms to be totally protected. Items brought into such areas can also be contaminated (53) with fungi from outdoors. The ventilation procedural practices in the patient's room and construction and maintenance practices must be carefully controlled throughout critical care facilities (54). (See Chapter 88.) Airborne Infectious Disease Control Negative-Pressure Isolation: Airborne Infection Isolation (AII) Room Hospitals often house patients who have infectious diseases spread by the airborne route in negative-pressure isolation rooms to prevent escape of pathogens from the room to surrounding areas (Table 89.3). Patients harboring M. tuberculosis can pose an occupational risk to the caregiver (see Chapter 37). With the development of antibiotic-resistant M. tuberculosis, infections may be difficult to treat and may be fatal in immunocompromised healthcare workers. During contagious stages of the disease, patients can create infectious aerosols by coughing, speaking, singing, or sneezing. The infectious droplets can dry in air to form droplet nuclei 1 to 5 В in size and float for long periods, increasing the probability of inhalation. A single inhaled tubercle bacillus may be able to produce an infection. Although tuberculosis patients must be isolated to minimize the risk of transmission of infection, the other infectious diseases spread by the airborne route also require isolation using special ventilation (9, 55). TABLE 89.3. INFECTIOUS DISEASES REQUIRING SPECIAL VENTILATION Herpes Zoster, disseminated Tuberculosis, pulmonary or laryngeal Varicella (chickenpox) In designing ventilation for isolation rooms, the area of the infected patient should be considered dirty (Fig. 89.4). The current strategy is to provide negative pressure to ventilate the room with exhaust exceeding supply by about more than 10% or by more than 125 cfm difference. It must be noted that the relatively low differential for air volume requires significant sealing of the room to prevent leakage. The room air should be exhausted to the outside or if returned for reuse should be filtered through a HEPA filter. This prevents air contaminated by the patient from escaping into the rest of the hospital and reduces the concentration of airborne tubercle bacilli within the room. Figure 89.4. Computer simulation of airflow pattern in a patient room that can be used to visualize air patterns in special ventilation rooms. In this example, airflow from the supply air covers the healthcare worker area, passing the “dirty” patient before exhausting. The room exchange rate has been studied with respect to particle removal (9); a point of diminishing returns is reached at about 12 to 15 room air exchanges per hour. The retrofit of older space to the higher air exchanges is difficult and not practical unless new design and construction are planned. To maintain relative pressures, one must ensure that the ventilation in place is working. The control of the airflow depends on the anticipation of exhaust systems deterioration from accumulation of dirt and lint on fan blades and turning vanes. Cleaning the air pathway and exhaust fans helps to ensure consistent pressure relationships. Installing effective negative-pressure ventilation is more challenging than installing positive-pressure ventilation. The negative-pressure system is easily compromised by air infiltration, and extra attention must be paid to sealing all ducts, doors, walls, and windows of the room. Even if the system is well sealed, it is more difficult to create directional airflow using suction. The clean (employee area) to dirty (patient area) airflow pattern should also be incorporated into isolation room design. The effectiveness of such design features, although intuitive and associated with clean room ventilation methods, must still be verified. There are difficulties in applying exhaust ventilation to clear a room of low concentrations of infectious particles. One study reported that when the concentration of microorganisms is low, a 14-fold increase in fresh air ventilation only reduces concentrations by 10% (8). Clearly, additional measures are required to make the room of the infectious patient safe. Source control measures, such as surgical masks for patients, local exhaust ventilation near the patient's head, and a respiratory protection plan for employees, are necessary for a comprehensive plan. UV light fixtures mounted high on the walls of the room have been shown to reduce the concentration of airborne bacteria. Riley et al. (56) demonstrated that a 30-watt UV light reduced airborne bacteria at a rate equivalent to 20 air changes per hour of mechanical ventilation. It must be remembered that when using UV light or portable filters to enhance ventilation for particle removal, the devices do increase equivalent room air changes for airborne infectious diseases control but do not satisfy fresh air requirements (13). Maintenance Considerations Design of sophisticated hospital ventilation systems must include ongoing routine maintenance as part of the budget for the project (14). Ventilation systems rapidly fail if not carefully installed, monitored, and repaired as needed. Deferred maintenance is a common problem in many hospital systems. In addition, sophisticated ventilation systems have failed to perform as specified because of inadequate installation. Failure to provide the designed supply of air in special ventilation areas by installing a fan with insufficient delivery capability will create ventilation deficiencies. Likewise, a void in the caulk around a window in a positive pressure room can allow windblown spores to enter the patient's room, bypassing the filtration system and exposing the patient. Improperly installed humidification or cooling systems can allow moisture buildup, creating ideal growth conditions in the air-handling system for potentially lethal mold. Poorly designed gaskets and mounting apparatus can allow dirty air to bypass the HEPA filters and contaminate clean areas. The failure to maintain the system may cause the air balance to change because of increased accumulation of lint and dust on filters; this may decrease the exhaust ventilation. Such changes could alter the negative air balance and cause the room to become positively pressurized (Table 89.4). TABLE 89.4. VENTILATION HAZARDS When designing a high-performance air-handling system, it is vitally important that all components are easily accessible for routine inspection and maintenance. Filter change-out must be performed according to safe maintenance practice (54). Filter efficiency actually increases during use as trapped particles increase the density of the filter media. At the end of a filter's useful life, it is so loaded with particles that it begins to impede system airflow. Monitoring devices such as manometers or gauges should be installed to measure the pressure drop across filters, and when the indicator exceeds manufacturer's specifications, the filter should be changed. Often, these measuring devices are not operable because of neglected maintenance (57). It is difficult to remove and replace the filter without dislodging P.1583 P.1584 P.1585 trapped contaminants and sending them downstream. The point-of-use filter (placed at the end of the duct just above the diffuser) in the bone marrow transplantation unit minimizes this effect by preventing more than 95% of the released particles from reaching the patient care area (58). Fans, cooling coils, and condensate pans must be readily accessible for cleaning and repairs. Studies and reports indicate that failure to design hospital HVAC systems with provisions for routine maintenance access can result in untoward clinical consequences (14). Training of personnel in the principles and importance of ventilation is essential. Often, maintenance personnel shut down critical fan systems without notifying persons in the affected areas. Such shut downs are a real threat because of the lack of ventilation control during those times. Fan systems must be routinely maintained, and shut downs must be carefully planned. Likewise, plans for emergency outages must also include provisions for backup motors or redundant systems. For example, contingencies for failure of the ventilation system in a bone marrow transplantation unit should include changes of procedural practice during the absence of ventilation control. For example, on the patient care unit, should the routine cleaning and patient visitation be temporarily suspended during fan outages? If malfunction is persistent, should supplemental ventilation be provided with portable systems? Such scenarios should also be considered for the ventilation for infectious disease isolation in anticipation of planned or unplanned outages. Finally, it is crucial that funds for ongoing maintenance and training are included in the hospital budget. Provisions must be made for additional patient protection during construction and remodeling projects (57, 58). When wall cavities are opened, large quantities of spores might be released from water-damaged areas hidden from view (59). Protective air environments must be secured from penetration by dust and debris generated during remodeling projects. During a large construction project at a Midwestern hospital, the infection control team purchased an optical particle counter to monitor the operating theaters and ensure that the ventilation system was controlling the air quality during construction (60). Microbiologic air monitoring can also be used, but baseline data must first be generated along with construction monitoring during the project. Results are often hard to interpret, and time spent would be lost to the more important aspect of monitoring the compliance to construction specifications related to infection control during construction. On the other hand, commissioning of ventilation systems by air sampling would ensure that specifications for filter installation and operation have been met. Verification of Ventilation Parameters for Special Ventilation Rooms Infection control airflow design specifications should also be verified (61). The parameters important for verification are associated with pressurization, room air exchanges, and filtration. Nicas et al. (62) and Rice et al. (63) showed considerable variation of airflow when special ventilation rooms were tested. Rice et al. reported large pressure variation for positively pressurized rooms primarily because of maintenance manipulation of dampers or fan belts. Negatively pressurized rooms had much lower pressure differentials and were considered more stable, but the airflow direction changed from negative to positive more frequently. The fluctuation from negative to positive was probably due in part to a low pressure differential at or about 0.25 Pa (250 Pa per 1.0 inch water gauge). Recently, Streifel and Marshall (64) clarified parameters that could be measured before occupancy of special ventilation areas. Table 89.5 is a listing of the parameters and notably the pressure measurements are listed. The pressure performance must be considered as a range because of constant variation of outdoor conditions, elevator movement, and doors being used. TABLE 89.5. RECOMMENDED MEASUREMENTS FOR SPECIAL VENTILATION ROOMS Testing and proving that airflow is appropriate, air exchanges are sufficient, and filtration is appropriate permit mechanical ventilation to be ruled out as a source for acquisition of Aspergillus. Other considerations can, therefore, be explored. Air Sampling Methods The nonviable airborne particle can be detected with the use of a particle counter, optical or laser, that allows real-time air quality analysis. It is important to differentiate particle sizes. The most useful devices for measuring particle sizes are those that determine particle size diameters greater than 0.5 Вm, 1.0 Вm, and 5.0 Вm per cubic foot. The particles at greater than 0.5 Вm are used for assessing a clean room, and Military Standard 209 (e) is used to classify clean rooms with particles per cubic foot less than a certain number. The classification is based on increments of 10, and a HEPA filtered (99.97% efficient at 0.3-Вm diameter particles) operating room or bone marrow transplant environment with no people should be capable of class 1,000 clean room status or better. The definition of a class 1,000 clean room is that there are less than 1,000 particles per cubic foot greater than 0.5 Вm in diameter. Such information is especially useful for ensuring filtration integrity or infiltration in a critical environment before the areas are occupied. These devices are useful for determining the cleanest areas. The class of the room designation can be a useful guideline but should not have such a specification for an absolute number that cannot be exceeded. The viable airborne particle analysis is more complex, because laboratory expertise is necessary. The selection of media, incuba P.1586 tion temperature, and skill for identification of environmental microbes are factors that must be considered if an environmental sampling program is initiated. The purpose for sampling should include determination of what the sampling is expected to evaluate. For example, an air-sampling search for human-shed microbes such as M. tuberculosis or staphylococcal species should not be considered because of the difficulty in culturing the slow growing M. tuberculosis and because staphylococcal species are frequently shed from humans. Aerosols generated by a medical device such as a drill may be instructive for air sample evaluations but certainly are not routine in any setting. Air sampling from a practical point of view should be considered only for evaluation of the presence of airborne fungi. Evaluation of the air for airborne fungi yields information that may be helpful in preventing infection or determining the source of airborne opportunistic environmental fungi. Sampling for airborne fungi should be used for determining the levels in areas where patients are at risk for infections from these opportunistic fungi. The media used for sampling a hospital environment should be capable of isolating clinically relevant microorganisms. Because the fungi are capable of growth on a variety of media, clinical media such as Sabouraud or inhibitory mold agar provides direct morphologic identification from the recovered isolates. Some environmental media, although excellent for total recovery, may require extensive subculturing for identification (Table 89.6). TABLE 89.6. MEDIA AND INCUBATION TEMPERATURES FOR CULTURING AIR SAMPLES Appropriate selection of growth media helps to expedite identification Sabouraud, Czapek, inhibitory mold agar, etc. Incubation temperature At 25ВC, greater numbers of airborne fungi will grow; lower temperatures help to distinguish infiltration or filtration deficiencies At 35ВC, the temperature selects for pathogen recovery; Aspergillus fumigatus and Aspergillus flavus are thermotolerant The presence of fungi capable of growth at body temperature is of particular concern. The difference between fungi that grow at room temperature (25ВC) and body temperature (37ВC) are generally greater than one order of magnitude except in highly filtered environments (Table 89.6). The most common in hospital exposure occurs from improperly filtered incoming air or from internal sources that were disrupted because of construction or maintenance. Air sampling will not prevent infections during construction. Air sampling can provide information that should inform infection control professionals that the air quality is good enough for safe patient care, because control measures are in place. It is difficult to detect the short-term high-dose exposures that occur because of environmental disruption. There are a variety of samplers capable of viable particle air sampling that include volumetric samplers and slit or sieve impactors. It is important that a volume of air is sampled. Settle plates depend on gravity, but single spores are less than 5.0 Вm in diameter and are buoyant aerodynamic particles. Clumps of particles settle, but perhaps the most problematic particles are those that are capable of entering the lungs. These respirable particles are less than 5.0 Вm in diameter. Collecting the particles in sufficient quantity is essential to detect low concentrations of spores causing nosocomial infection. Arnow et al. (14) reported infection rates of about 1.2% with Aspergillus flavus and A. fumigatus at 2.2 and 1.1 colony-forming units (CFU)/m3, respectively. Rhame et al. (65) reported a 5.4% infection rate with A. fumigatus at 0.9 CFU/m3. A major problem with most samplers used in hospitals is low sample volume capability. Most samplers are designed to sample dirty environments. Samplers that sample 1 cfm may fail to detect spores at levels less than 1.0 CFU/m3. Hospital air samples should be at least 35 cubic feet or 1.0 m3 to detect low levels of spores. Disadvantages of many samplers include low-volume sampling, drying of media with long sampling times, difficult manipulation of culture plates, and difficult calibration. A slit to agar sampler with a timer up to 60 minutes may be the best choice of sampler dependent on the type of timer, noise levels, and portability. Interpretation of Data Timing for detecting airborne fungal levels is important for interpretation of results. For example, activity evaluation with an air sampler may reveal high concentrations of airborne fungi during renovation activity of a water-damaged bathroom. The best use of air sampling is before occupancy to determine proper filter installation and room pressurization. The purpose of such sampling is to establish rank order for the cleanest areas. The best filtration should demonstrate the lowest particle or viable airborne fungal counts. Such numbers are best demonstrated as baseline before occupancy. Subsequent sampling should take into account people and conditions such as incorrect airflow in a protective environment. Exposure to high levels of an airborne infectious agent over a short time is probably the greatest risk to the host. The ability to capture such events is difficult. The sampling of the environment should be to determine if the ventilation systems work according to specification. Therefore, the areas with the best filtration, pressurization, and air exchanges should have the lowest airborne fungal counts. This should also be true for nonviable airborne particles detected with a particle counter. If pathogens (A. fumigatus, A. flavus, or other opportunists capable of growth at body temperature) are recovered from protected environments, consideration should be taken for single-plate hits versus multiple-plate hits from pathogenic fungi. Random isolate recoveries may be represented by a single colony on a plate. Greater than two colonies, for example, A. fumigatus, may represent a point source within the patient care environment. Repeat sampling under such circumstances should determine if it was a passing phenomenon (Table 89.7). TABLE 89.7. INTERPRETATION OF AIR SAMPLE DATA Rank order determination Clean to cleanest with the lowest counts in the areas with proper ventilation control (pressure, air exchanges, and filtration) Lowest counts in the areas with best filtration. Comparison data necessary (outdoor vs. lobby vs. patient care area) Indoor-to-outdoor ratio I/O <1 normal I/O >1 potential problems. Consider outdoor conditions and comparison data colony types Qualitative information Pathogen recovery with results >1 CFU pathogen per plate a potential indoor source Comparison to determine homogenous versus heterogeneous population Temperature selectivity Pathogens grow at temps >35ВC Total fungi more sensitive to I/O at 25ВC CFU, colony-forming unit. Interpretation of the results from air sampling requires a comparison of sample locations. If sampling is requested, the cleanest environment (i.e., operating rooms or bone marrow transplant unit) should have the lowest numbers of microorganisms recovered. The basic comparison should be from clean to cleanest in CFU/m3. For better results, such comparisons should be done with culture media incubated at room P.1587 temperature. Room temperature incubation at about 25ВC is more sensitive for fungal recovery. The comparison samples for detecting filtration integrity or potential infiltration should also be incubated at room temperature. Qualitative analysis, however, of airborne pathogens such as A. fumigatus is better at close to body temperature (>35ВC), because the other mesophilic fungi are inhibited, allowing the pathogens to be more easily detected. The pathogens are easily obscured when the samples are incubated at room temperature. Also, the rank order comparison is difficult at the higher temperature, because the differences in levels in highly filtered areas are not very great. For example, the difference in recovery from media incubated at room temperature for samples taken from the nurses' station in the bone marrow transplant unit versus those taken from HEPA-filtered rooms might be 55 and 4 CFU/m3, whereas the same samples incubated at 35ВC might yield 10 and 4 CFU/m3, respectively. The samples incubated at room temperature are intended to demonstrate ventilation deficiencies, whereas the samples incubated at body temperature should be able to detect pathogens. Pathogen content should be less than 1.0 CFU/m3 with repeat sampling. Invariably A. fumigatus shows up as a single isolate with few, if any, other microorganisms on the sample plate. A combination of factors that demonstrate the cleanest environment with the lowest pathogen counts are important for data interpretation. The value of comparisons with outside recoveries is that levels of A. fumigatus are often higher outside the hospital than inside, for example, 9.0 versus 1.0 CFU per sample. When adjusted for CFU/m3, outside samples have much higher levels than inside, allowing an indoor-to-outdoor ratio of less than 1. However, if the inside levels are higher than outside levels (except during snow cover or after rain), then an internal source may be suspect. The recovery of two or more colonies of a pathogen from media incubated at 35ВC may indicate an internal point source (66). CONCLUSIONS It is important that infection control, environmental, engineering, and maintenance personnel actively monitor the proper operation of the HVAC system. Smoke tubes can be used to demonstrate airflow movement in special ventilation areas. However, new instruments are capable of measuring very low pressures and should be incorporated into the quality measures necessary for a safe environment of care. All maintenance, surveillance, repair, and construction activities should be coordinated in such a manner as to ensure that precautions to protect the health and well-being of all patients and staff are implemented. Use of pressure (airflow direction), room air changes per hour, and filtration verification specifications are essential for effectively maintaining protective and airborne infection isolation environments. Protection from Bioaerosols Concern for the protection of buildings is imminent especially because terrorism is part of the current state of affairs in the world order. Planning to provide an upgrade of building systems for protection certainly is being considered as part of the National Bioterrorism Hospital Preparedness Program. Hospitals should consider such planning; however, certain preparedness for fire protection and common sense planning for natural microbial agents (pathogenic Aspergillus species) will certainly help to prepare healthcare buildings for such events. Previous sections of this chapter consider the ventilation requirements for airborne infection isolation. For rooms, the described ventilation parameters will help maintain individual room control of microbial agents spread by the airborne route. The concern for the emergency room waiting areas and sections of the hospital needing to house potentially infectious patients is a challenge. Current fire code requirements for smoke control will aid in the development of a strategic plan for isolating a ward. Hospitals are segmented into smoke control zones, which are smoke compartments. These zones have ventilation dampers and fire stopped walls that will evacuate smoke if fires are detected in that zone. Engineering concepts are being explored to use the smoke control dampers and exhaust systems to help isolate the areas with infectious agents. The criteria for isolation would not be as extreme as the smoke management requirements, but the mechanism should already be in place for establishing the depressurized zone for an AII patient care unit. These concepts will help to establish such areas without the excess cost for configuring an area that may never be required. NIOSH has published a listing of building preparation tasks, if implemented, would help to protect from naturally occurring airborne infectious agents: http://www.cdc.gov/niosh/bldvent/2002-139.html http://www.cdc.gov/niosh/docs/2003-136.pdf It is vitally important to focus on what works, especially on what works consistently. To provide the best possible hospital air quality, state-of-the-art technology is needed. 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An evaluation of hospital special ventilation room pressures. ICHE 2001;22:19–23. 64. Streifel AJ, Marshall JW. Parameters for ventilation controlled environments in hospitals. In: Design, construction, and operation of healthy buildings. IAQ/1997. Atlanta: American Society for Heating, Refrigerating and Air-Conditioning Press, 1998. 65. Rhame FS, Streifel AJ, Kersey JH, et al. Extrinsic risk factors for pneumonia in the patient at high risk of infection. Am J Med 1984;76:42–52. 66. Streifel AJ. Air cultures for fungi. In: Isenberg HD, ed. Clinical microbiology procedures handbook. Washington DC: American Society for Microbiology Press, 2003:13.9.1–13.9.7.
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PATIENT SAFETY, HEALING ENVIRONMENTS AND INFECTIOUS RISKS Patient Safety Initiatives The Institute of Medicine's (IOM) first report on patient safety in 1999 seized the nation's attention, focusing on the importance of the healthcare environment's effect on patient outcomes (1). The Agency for Healthcare Research and Quality (AHRQ) was charged with developing a plan to reduce adverse outcomes and improve the safety of workers and patients. This focus on medical safety continues to develop in healthcare organizations across the United States (2). Care delivery processes occur in physical structures intended to be healing environments, enhancing patient's health outcomes. Coincident with the emphasis on patient safety, accreditation agencies such as the Joint Commission on Accreditation of Healthcare Organizations (JCAHO) also encourages facilities to ensure that the environment of care (EOC) in facilities does not serve as a reservoir for pathogens. Implicit in this emphasis on the EOC is preventive maintenance for critical utility systems that deliver ventilation and water to patient care areas. Microbial Hazards Associated with Construction and Renovation The physical environment in a healthcare facility may pose risks to occupants (e.g., patients, personnel and visitors), if enhancements to the environment are carried out without a basic understanding of the potential for creating hazards and the associated morbidity and/or mortality. Physical hazards, infectious risks among them, may occur as the result of well-intentioned designs that may have unexpected consequences. For example, hospital epidemiologists need to balance proposals for a water feature such as a water wall, with potential risks of disease from water-borne opportunistic infectious agents such as Legionella species. A clearer picture of infectious hazards associated with care delivery environments has emerged over the past decades. Healthcare epidemiologists and other infection control professionals (ICPs) are increasingly recognizing that such risks may occur during construction, renovation, or preventive maintenance or from damage following natural or manmade disasters. New knowledge gained from disease outbreaks and successful interventions can be incorporated by architectural and engineering communities to improve designs, resulting in truly healing environments. It is essential that architects, engineers, healthcare epidemiologists, infectious disease specialists, infection control (IC) personnel, safety specialists, and others balance planning for construction and renovation with a thorough knowledge of infectious hazards, preventive techniques, and effective interventions to ensure the safest and most patient friendly environment. Rubin et al. (3) analyzed reports in the literature describing associations between the EOC and occurrence of infectious diseases. Of the reports in this review, almost all were observational and the few randomized controlled trials that were conducted had small sample sizes and lacked statistical power thereby precluding definitive conclusions. Therefore, most knowledge from studies of the role of the EOC on healthcare-associated infections (HAIs) is derived from investigation of clusters of disease. This evidence suggests that an overall cause-effect relationship does exist between healthcare environmental factors and therapeutic outcomes, but it is evident that there is a great need for more research. These experiences do provide information on mitigating risks and designing the EOC to prevent disease transmission. Airborne Microorganisms Most studies that have associated disease transmission with construction or renovation have involved improper ventilation design or maintenance that allowed exposure of highly immunocompromised populations such as bone marrow transplant patients to opportunistic pathogens (e.g., Aspergillus species). Airborne infectious agents (e.g., Mycobacterium tuberculosis) affect the health of patients and healthcare personnel (HCP). Insights gained from infectious diseases outbreak investigations have been used to mitigate risks of nosocomial exposure during construction or renovation. Interventions that were frequently associated with decreased infection rates or that terminated outbreaks have been steadily incorporated as standard design requirements by guideline-setting agencies (4, 5). Selected examples of risk mitigation or prevention are summarized in this section to underscore the importance of specific design issues such as controlling dissemination of particulates and airborne pathogens during demo P.1550 lition and ensuring that the design of heating, ventilation, and air conditioning (HVAC) systems meet the needs for general and special patient care areas [e.g., operating rooms (ORs), interventional cardiology units, and airborne infection isolation rooms (AIIRs)]. Sources of airborne contaminants and infectious agents are closely related with water- and moisture-related conditions. Representative outbreaks are also discussed considering primarily the major mode of infectious agent transmission. Construction and Airborne Sources Air quality management during construction is key to preventing transmission of opportunistic microorganisms to susceptible patients, most notably highly immunosuppressed patients. Key publications of outbreaks related to Aspergillus species and related fungi received increased attention in the 1970s and are summarized elsewhere (6, 7) (see Chapter 60). Transmission of airborne infectious agents may originate from patient reservoirs (Chapter 37), from laboratories and autopsy rooms (Chapters 82 and 84), and from dust and soil introduced into the facilities during construction (8, 9). The relationship between facility HVAC and airborne nosocomial infections is discussed elsewhere in this text (Chapter 89). Numerous studies have confirmed the process by which construction activity brings outdoor contaminants into a building normally “protected” by multiple systems. Key findings from investigations describing airborne microbial contamination associated with construction between 1976 to 2002 are summarized in Table 88.1 (10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61). TABLE 88.1. AIRBORNE MICROBIAL CONTAMINATION ASSOCIATED WITH CONSTRUCTION–SELECTED STUDIES BY YEAR AND MICROORGANISM Soil and dust become vehicles for particulates, which carry microorganisms, leading to infection and disease in specific populations. This process has been described in several excellent studies (23, 24, 62, 63). Dust particles from excavation (aside from irritation from fumes and chemicals) become the vehicle for introducing opportunistic microorganisms into the air handling systems or HVAC (33, 64). External Demolition and Implosions. Excavation has been cited as the major problem with external demolition and implosions (65). Recent reports regarding the impact of large-scale demolition (e.g., implosion) have provided important new information about whole-building HVAC and air pressurization. Facility-associated cases of aspergillosis have been related to depressurization, drawing contaminants into a facility adjacent to another building that was imploded (54, 66, 67) (see Chapter 89). Intrusion of contaminants during nearby building implosions producing larger than normal burdens of dust and contaminants has been measured; proper planning can reduce the risk from this increased burden (68, 69). Preemptive measures include cancelling elective surgery for patients at high risk, sealing windows and doors, additional filtering, and maintaining positive air pressure for special areas. A fire in a nearby building may also have resulted in transmission of Aspergillus species through open windows by imbedding spores in carpeting (36). Indoor Environment. Aspergillus species and Rhizopus are among the most important fungi introduced during construction and are characterized by an ability to grow in an indoor environment under favorable temperature and moisture conditions (13, 14, 24). Other fungi that gain access through building penetrations include Penicillium species, Cladosporium species, and similar airborne contaminants (33, 63, 70). Air Handlers. Many publications have addressed the importance of appropriate air handling during construction to reduce the risk of transmission of airborne pathogens such as Aspergillus species to susceptible patients. Appropriate air handling includes zonal use of high-efficiency particulate air (HEPA) filters, provision of negative air pressure (39, 45, 71, 72), dedicated exhaust, and physical isolation of the construction area from patient care areas (24, 32, 40). Numerous patient outbreaks of bacterial and fungal infections associated with aerosols from contaminated ventilation ducts, grills, damaged barriers (e.g., bird screens, ventilation fans), and vacuum cleaners reinforce the importance of maintaining an intact air handling system (11, 43, 50). Room Design and Location. Room design must consider location of supply air and exhaust vents, critical determinants in transmitting airborne contaminants (33, 41). Negative air pressure in pediatric oncology units, for example, was shown to reduce the spread of varicella-zoster virus (VZV) among workers and patients (16). Lower bloodstream infection and mortality rates were reported for burn patients in enclosed intensive care unit (ICU) beds than for patients in open wards (73). Multiple outbreaks related to M. tuberculosis were terminated with properly designed and improved maintenance of negative air pressure (isolation) rooms (74). The Surgical Suite Environment. The OR environment has been studied extensively in an attempt to reduce infectious risks in patients undergoing orthopedic joint replacement. The literature on reductions in surgical site infection (SSI) rates, primarily found in total joint arthroplasty, is reviewed elsewhere (75, 76, 77). The focus for this chapter relates to contamination of the OR during construction and renovation from airborne fungi and other pathogens (27, 28, 31, 78, 79, 80, 81, 82, 83, 84, 85). A summary of the general issues and interventions to mitigate these problems have been reported elsewhere (8, 9, 28, 82, 86) (see Chapter 89). Multiple interventions in ORs have led to steady reductions in infectious outcomes for surgical patients. As a result, current standards include increased outside air and total air exchanges per hour, improved air filtration efficiency, proper humidification, and filter location in air handlers serving ORs (15, 31, 42). Major studies by Lidwell (87, 88) focused on the use of ultraclean (laminar airflow) HEPA-filtered air in clean orthopedic surgical procedures. These studies, together with other multisite studies (80, 89), led to a better understanding of the independent contribution of ultraclean air in reducing clean SSIs; its effect is comparable to the use of preoperative prophylactic antibiotics. Accordingly, laminar airflow HEPA filtration may be considered for specific high-risk populations to reduce SSIs. However, definitive evidence on efficacy of elaborate laminar airflow in prevention of SSIs is lacking. Water-Borne Microorganisms Contaminated water can be a source of water-borne pathogens. Those at greatest risk are immunocompromised patients, P.1551 P.1552 P.1553 and many outbreak investigations have identified potable water systems and storage tanks, shower heads, and ice machines as sources of water-borne pathogens (90, 91, 92, 93). Table 88.2 summarizes findings from investigations of clusters of infection caused by water-borne pathogens (92, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111). Legionella species, for example, have been implicated in patient infections acquired through inhalation of aerosols spread from contaminated storage tanks, shower heads, and equipment that used tap water, such as water baths, and/or entire water systems (103, 112, 113, 114, 115, 116). A review of nosocomial water-borne infections excluding those caused by Legionella species revealed 43 outbreaks with associated deaths of almost 1,400 per year and called for provision of sterile rather than potable water for high-risk patients during hospitalization (117). Maintenance of drinking water quality depends on good design and preventive maintenance and surveillance for nosocomial infections that includes a high index of suspicion for infectious agents associated with moisture and water distribution systems. One study assessed the risk of bacterial pathogens in drinking water in an attempt to determine if dose-response relationships could be developed, and whether or not potable water poses a public health hazard (118). The results included a ranking of water-associated microorganisms from P.1554 studies reported primarily from medical centers. Although the purpose of the study was not directly related to construction, the review does confirm the expected frequency of opportunistic microorganisms causing serious infections associated with water. These opportunistic microorganisms are of concern because of their potential for direct or indirect transmission from taps and sinks or through inhalation of aerosols generated from construction activities. Even contaminated condensation from window air conditioning units when combined with other work practices can lead to invasive infections such as Acinetobacter species bloodstream infections in high-risk pediatric populations (119). TABLE 88.2. WATER-ASSOCIATED CONTAMINATION ASSOCIATED WITH CONSTRUCTION—SELECTED STUDIES BY YEAR AND MICROORGANISM Moisture and Fungi Excessive moisture around pipes and insulation, condensation in drain pans, and flooding from broken pipes can lead to extensive environmental fungal contamination. Such contamination has been associated, for example, with water-soaked cabinets in medication rooms (23, 62). Static water systems can provide a reservoir of microorganisms in the healthcare environment by supporting their growth. Nonsterile water used for invasive patient-related procedures can result in direct or indirect transmission of microorganisms to patients (92, 98, 120). A recent report of fungal endophthalmitis from Acremonium kiliense following cataract surgery in an ambulatory surgery setting demonstrated the process by which contaminated humidifier water functioned as a reservoir for an infectious agent eventually spreading through the airborne route by way of the ventilation system (42). Typically nosocomial transmission of fungi is airborne; however, there is emerging evidence that potable water in health facilities may also be a significant reservoir, suggesting that prompt disinfection of high water-use areas such as showers is an important measure to prevent exposure to fungal pathogens (121). Legionella Species Annually there are estimates of between 8,000 to 18,000 hospitalizations for legionellosis (122). However, reported hospital outbreaks predominate in the literature because of the fatal effects on susceptible patient populations; they have helped characterize Legionella and identify key risk factors from affected individuals (123, 124, 125, 126). Although each reported outbreak of legionellosis improved the epidemiologic profile of this pathogen, endemic, sporadic cases (representing most of the observed cases) still evade full understanding. The mode of transmission implicates not only cooling towers, potable water reservoirs, and distribution systems (124, 125, 127, 128) but also water-related equipment (e.g., medication nebulizers) (129) and potable water used for nasogastric feeding (93). Legionella species from nearby environmental water sources enter hospital water systems, multiply in cooling towers and evaporative condensers, and/or contaminate the potable water system. Because infection develops after inhaling airborne water droplets containing Legionella species, any opportunity for contaminated water to aerosolize is of concern during construction and renovation. Major construction has been associated with numerous nosocomial outbreaks or clusters (112). Potential mechanisms include release of this microorganism from vibration or significant changes in water pressure. These disturbances loosen corrosion and disturb biofilms thereby releasing Legionella species in water system pipes. Excavation permits the microorganism to be released from the soil; the microorganisms eventually enter cooling towers, air intakes, or water systems, leading to direct inhalation from water sources (130). Summaries of outbreaks have been described in the Centers for Disease Control and Prevention (CDC) guidelines and other government and private recommendations for detection and treatment (130, 131, 132, 133, 134, 135). CHANGES IN HEALTHCARE DELIVERY AND IMPACT ON CONSTRUCTION TRENDS Construction Costs Annual construction and design surveys in the United States indicate a continued major expenditure on healthcare construction and renovation. Changes in patient acuity, aging, and reduced capitol funds have affected construction expenditures in a number of ways. Recent trends show dollars are spent primarily on inpatient specialty beds (e.g., cardiac and cancer) along with increasing demands for assisted-living and skilled nursing centers. Construction for hospitals, nursing homes, and outpatient facilities in 2001 totaled 3,362 projects, at a cost of $15.7 billion (136). However, 76% of the projects involved either expansion or renovation at a cost of $8.7 billion—more than half of total construction expenditures. The increasing age of U.S. healthcare facilities generates a constant need for repair and remediation work (cabling, room additions). These processes increase risks of environmental contamination, affecting air and water quality. Natural disasters (e.g., flooding) add additional opportunities for contaminating healthcare delivery sites. New concerns for protecting buildings from airborne contaminants from intentional release of biologic agents or unintended manmade disasters have focused additional attention to the building envelope, ventilation management, and the isolation room capacity (137, 138). Costs of Healthcare-Associated Disease Outbreak investigations documenting health outcomes resulting from contamination are associated with multiple healthcare settings but focus primarily on hospitals. Although the actual percentage of HAIs directly related to construction is unknown, one can consider costs in terms of one significant airborne infectious agent, Aspergillus species. Aspergillus can be either community-acquired or nosocomial, but it is difficult to always distinguish between them. The total cost impact is enormous. For example, in considering aspergillosis alone for 1 year (1996), costs were estimated at $633.1 million. Although the number of aspergillosis-related hospitalizations are a small percentage of the total hospitalizations (10,190 hospitalizations; 1,970 deaths), the average length of stay (LOS) attributable to treating this disease is 17.3 days, costing an average $62,426 [95% confidence interval (CI) $52,670 to $72,181] based on 176,272 hospital days (95% CI 147,163 to 206,275 days) (139). P.1555 The case fatality rate for aspergillosis averages 58%, but for bone marrow transplant recipients it reaches 86.7% (140) (see Chapter 60). A better assessment of risks and their mitigation can enable architects to design and plan for patient-friendly and safer facilities. DESIGNING FOR DISEASE PREVENTION AND HEALTH PROMOTION Healthcare Study Design This section focuses on design and construction of healthcare environments that plan to reduce risks of adverse outcomes learned from past experience and that emphasize infection prevention and control during new construction and renovation (external and internal). Suggestions and recommendations to prevent and control infectious risks are based on published investigations occurring most frequently in hospitals; these recommendations may need tailoring for other healthcare delivery sites. Design professionals are increasingly interested in identifying individual variables that affect patient outcomes and worker productivity, forming a growing science around the relationship between the built environment and quality of care (141). The built or physical environment is defined as any aspect of the environment that is constructed by design experts such as architects or designers. More attention is being given to designing facilities that are cost-effective, efficient, and functional for staff while cultivating a caring, healing environment for patients. Collaborative efforts between the Picker Institute and the Center for Health Design resulted in initiatives to analyze and improve patient outcomes (142, 143). Focus groups identified properties that were important for healing and well-being of patients in acute, ambulatory, or long-term care settings. Participants identified the need for an environment that enables a connection to staff, is conducive to well-being, is convenient and accessible, allows confidentiality and privacy, cares for the family, is considerate of impairments, provides connection to the outside world, and provides safety and security. It is noteworthy that participants identified physical conditions only in terms of comfort (temperature, lighting, and cleanliness) but not in terms of illnesses (e.g., M. tuberculosis associated with ventilation structures). Although numerous studies have reinforced the importance of a safe physical environment, patient perceptions have a powerful—but not always measurable—impact on patient outcomes (142, 143). Current and Future Design and Materials Because of the paucity of scientific evidence, ICPs must rely on fundamental principles such as the epidemiology of infectious diseases to determine what interventions are most likely to be effective in preventing infection. Evidence from prevention of HAIs through use of antimicrobial-impregnated medical devices is leading to incorporation of antimicrobial surface or polymer treatments to minimize environmental reservoirs of potential pathogens (144, 145). Other architectural and utility system features under study include ventilation systems that provide 100% exhaust, design of microbial-resistant building materials (e.g., glass mat faced gypsum board), use of ultraviolet germicidal irradiation to prevent biofouling of air handling units, and design features that minimize buildup of biofilms in potable water systems (146). Of the published studies with better research designs there were findings that environmental features can correlate with health outcomes; therefore, improvement in outcomes may be possible through design interventions that are guided by sound scientific inquiry. However, studies that contain data about the effect of the environment are surprisingly scarce. The need for broadened research is striking; many factors have never been investigated. Many studies have significant flaws that render conclusions suspect or cast doubt on the ability to generalize the findings to other populations. Future research should be more carefully designed to ensure that groups of patients being compared under various conditions do not differ in other ways, thus preventing skewed results. Current efforts include designing the safest possible hospitals in the broadest sense of safety (147, 148, 149) and considering IC issues in design (145, 150). A number of engineering studies directed at determining ideal ventilation for patient rooms (151) or AAIRs (152) have provided a foundation for design recommendations (153). Additional studies of areas needing special ventilation such as the OR suite have and will continue to drive changes in specific parameters for consensus guidelines. Interestingly, a computer modeling study of efficacy of OR HVAC design found that increasing the number of air changes per hour was not as important as air velocity, and unidirectional airflow at the surgical site was more important than location (high or low) of exhaust ducts (154). Floor covering materials such as carpeting have been studied extensively, and, although it is colonized with a variety of pathogens (e.g., Clostridium difficile), no direct link to patient infections has been found (36, 155, 156). Accordingly, carpet in patient care areas should be chosen with respect to aesthetics and cleanability and not because of risk to patients. Current interest in surfaces and treatment or incorporation of antimicrobial products into the surface matrix to inhibit microbial growth are available commercially. However, most efficacy studies involve in vitro investigations; more research is needed to determine if such measures can prevent HAIs (157). REGULATORY AND ACCREDITATION AGENCIES' GUIDELINES AND STANDARDS THAT IMPACT CONSTRUCTION Agencies with Impact on Design and Physical Environment Standards and guidelines issued or enforced by the following agencies have had major impact on the physical structure of healthcare settings. There are many agencies and professional associations that have a direct impact or provide resources to plan, design, and better construct facilities; some of note include the following: American Institute of Architects/Academy of Architecture for Health and the Facilities Guideline Institute (AIA/AAH/ P.1556 FGI): “2001 Guidelines for Design and Construction of Hospitals and Healthcare Facilities”—minimum standards for most states (4) Centers for Medicare and Medicaid Services (CMS), formerly Health Care Finance Administration (HCFA): “Hospital Conditions of Participation (COP)”—for Medicare and Medicaid (158) JCAHO: “Comprehensive Accreditation Manual for Hospitals: The Official Handbook” (159) CDC/Healthcare Infection Control Practices Advisory Committee (HICPAC): “Guidelines for Environmental Infection Control for Healthcare Facilities” (160) and numerous other guidelines (5, 161, 162, 163, 164) Other agencies Occupational Safety and Health Administration (OSHA): tuberculosis, construction, bloodborne pathogens, and legionellosis (133, 165, 166) National Institute of Occupational Safety and Health (NIOSH): HVAC, sharps containers, and air sampling (167, 168, 169) State and local standards (170) Professional organizations with resources and/or standards Association for Professionals in Infection Control and Epidemiology (APIC): state-of-the-art report (SOAR); infection control risk assessment (ICRA) (8, 9, 171) American Society of Healthcare Engineering (ASHE): contractor certificate program including ICRA; monographs American Society of Heating, Refrigerating and Air-conditioning (ASHRAE): basic design research; design handbooks Relationship between AIA/FGI Guidelines and Regulations Changes related to facility design aimed at reducing infectious risks are evident in many of the revised standards. For example, the 2001 AIA/FGI guidelines (minimum standards) added explicit requirements for design consideration termed an ICRA. CMS requirements are consistent with the AIA/FGI guidelines, although CMS uses additional physical plant standards to enforce the COP and the Life Safety Code (LSC), currently the 2000 LSC. In addition to CMS, more than 40 states adopted the AIA/FGI guidelines as minimum design standards or adapted them with state-specific regulations governing physical plant and safety issues, transforming guidelines to regulatory status. Facilities accredited by JCAHO must consider the EOC standards that became effective January 1, 2001, because these impact utility management standards for all facilities. In 2002, JCAHO added specific standards for design and construction that reflect the 2001 AIA/FGI guidelines requirement for a risk assessment that state, “When planning demolition, construction, or renovation work, the hospital conducts a proactive risk assessment using risk criteria to identify hazards that may potentially compromise patient care in occupied areas of the hospital's buildings. The scope and nature of the activities should determine the extent of risk assessment required. The risk criteria should address the impact demolition, renovation, or new construction activities have on air quality requirements, IC, utility requirements, noise, vibration, and emergency procedures. As required, the hospital selects and implements proper controls to reduce risk and minimize impact of these activities” (159). The CDC guideline for environmental IC supports many key guidelines and recommendations and provides strength-ranked recommendations based on peer-reviewed scientific evidence (160). AIA/FGI: Key Design Agency The AIA/FGI with assistance from the U.S. Department of Health and Human Services publishes minimum guidelines that have been wholly adopted by most states and the Indian Health Service; the remaining states accept them with some modifications. Chapters address outpatient care sites, nursing homes, hospice, assisted living, and rehabilitation settings in addition to the basic hospital guidelines. Although the 1996 to 1997 Guidelines for Design and Construction of Hospitals and Health Care Facilities required an ICRA, the impact was narrowly confined to determining numbers of AIIRs (172). The AIA/FGI 2001 guidelines expanded ICRA based on the facility's patient or resident population and programs (4). INFECTION CONTROL RISK ASSESSMENT—DESIGN AND CONSTRUCTION ASPECTS Concept—The Infection Control Risk Assessment Infection Control Risk Assessment—Construction Projects The AIA/FGI guidelines recognize that renovation and new construction in existing facilities can create conditions that may be hazardous to occupants. The 1996 to 1997 edition of the guidelines required construction and major renovation assessments during project planning related to specific risks. The current 2001 guidelines lend stronger weight to IC input at the initial stages of planning and design of a project by requiring documentation of an ICRA (4). The ICRA is considered a process requiring documentation of continued involvement of IC throughout specific projects. ICRA is a determination of the potential risk of transmission of various agents, particularly biologic, in the facility but expands far beyond determining optimal numbers of isolation rooms or location of hand washing stations. Instead, ICRA supports design of the EOC toward systems that prevent transmission of infection and ensures a safe environment for patients, personnel, and visitors. For example, an important component of ICRA is determining locations and installation of dedicated exhaust when cleaning and disinfection of medical equipment is anticipated. Furthermore, preliminary evidence suggests that ICUs with a central nursing station surrounded by private rooms permits easy visualization and response to rapid changes in patient status (150). Such architectural arrangements, although not directly related to preventing disease transmission, enhance spatial separation of patients and facilitate communication thereby improving safety for patients and personnel. P.1557 The 2001 guidelines state that “the ICRA shall be conducted by a panel with expertise in IC, risk management, facility design, construction, ventilation, safety, and epidemiology. The panel shall provide documentation of the risk assessment during planning, design, and construction. The ICRA shall only address building areas anticipated to be affected by construction. The design professional shall incorporate the specific, construction-related requirements of the ICRA in the contract documents. The contract documents shall require the constructor to implement these specific requirements during construction” (4). The specific elements to be addressed include the following: Impact of disruption on patients and employees Patient placement or relocation Placement of effective barriers to protect susceptible patients from airborne contaminants such as Aspergillus species Air handling needs in surgical services, airborne infection isolation and protective environment (PE) rooms, laboratories, local exhaust systems for hazardous agents, and other special areas Determination of additional numbers of airborne infection isolation or PE rooms Consideration of the domestic water system to limit Legionella species and other water-borne opportunistic pathogens ICRA and Long-Range Planning and Design Although the ICRA as described by the guidelines is basic, it is equally important to step back and consider the long-range planning that goes into the overall master facility plan and the critical need for early and continuous input from IC. Although the language of the ICRA clearly calls for input during planning, it is applied most frequently to specific projects. APIC published a strategy in 2000 for assessing healthcare facilities for infectious risks during construction in the APIC SOAR on construction and renovation and recommended an ICRA similar to that later required by AIA/FGI guidelines and in the draft CDC environmental IC guidelines. However, the tactics begin with developing a construction and renovation policy (CRP), a multidisciplinary team, and a process to implement the policy (9). Once a system is in place providing for oversight, the application of the guidelines fit into each specific project. The guidelines require documentation of an ICRA for each specific project; they are not retrospective and apply only to new construction or major renovation. However, the approaches may be applied to smaller repair or preventive maintenance projects as appropriate. Thus, development of a broad-based CRP is an efficient and effective method to address basic principles that affect all projects, using the CRP as reference point for the facility. Recommended resources for a CRP include the AIA/FGI guidelines, the CDC environmental IC guidelines, the APIC SOAR, and Canadian guidelines for Aspergillus and Legionella. Infection Control Risk Assessment—Overview for Planning and Design Teams Multidisciplinary planning committees vary according to the size, although all resources agree that an assessment panel must include professionals with expertise in IC, risk management, facility design, construction, ventilation, safety, and epidemiology. The panel is most effective if it includes an administrator and major stakeholders such as environmental services and the patient care manager most affected by the construction or renovation. If a CRP is developed and approved, it becomes the basis of the ICRA for major or minor processes. A key first step is identification of a multidisciplinary planning group involving design professionals, engineers, risk and safety, IC and epidemiology, the IC committee (or committee charged with development and review of the IC policy), and administrators representing special program needs. Construction and Renovation Policy A comprehensive CRP requiring IC input is the fundamental strategy that ensures timely notification of the ICP (or person with IC responsibilities) for early program planning. Once established, the ICP should be made aware of planned projects as a matter of routine. This in turn ensures that an IC evaluation of the project will be provided from concept to completion as now required by the ICRA. The evaluation should include design of the EOC, construction preparation and demolition, intraconstruction operations and maintenance, project completion with postconstruction cleanup, and monitoring. The ICRA documentation process fits future projects from small to complex (8, 171). Construction and Renovation Policy Elements The policy should address overall planning, designing, and monitoring processes, anticipating that future projects will vary in degree of complexity. It should ensure that input is required in all phases (i.e., structural design and specific practices to protect occupants during the preconstruction, intraconstruction, and postconstruction phases). Basic issues include the authority and responsibility for establishing internal and subcontractor coordination of each stage of the project. The policy should be submitted for approval by the facility's board of trustees and reviewed and approved periodically (e.g., annually). Specific elements that should be included in the policy include the authority and responsibility for establishing internal and subcontractor coordination of (a) construction preparation and demolition, (b) intraconstruction operations and maintenance, (c) project completion and postconstruction cleanup, and (d) monitoring. A comprehensive policy is the basis of individual project ICRAs. The CRP should also anticipate remediation responses in the event of major disruptions. Elements include the following: Authority and communication lines to determine if or how patient unit closure will occur Planning for air handling and water systems and plumbing as appropriate Expectations for contractor accountability in the event of breaches in IC practices and related written agreements Patient area risk assessment—location or admission criteria P.1558 Criteria for emergency work interruptions (stop and start processes) Education: for whom and by whom Occupational health expectations for subcontractors before start, as needed Traffic patterns for patients, HCP, and visitors Transport and approval for disposal of waste materials Emergency preparedness plans for major utility failures with IC implications, including location and responsibilities Commissioning—what testing will be done to determine that delivered projects meet the owner's expectations Monitoring processes Integration of the CRP and ICRA Once approved, a CRP becomes the ‘driver’ to ensure appropriate and continuous input from IC into (a) the structural design processes to identify appropriate and timely IC practices and (b) involvement in specific projects during each construction phase, focusing on patient and worker protection from construction activity. Infection Control Risk Assessment—Design Population Assessment Long-range planning for major new construction projects begins with assessments of the organization's patient population to identify the type and structure needed by defined programs. For example, an elderly population requires different support structure than an organ transplant unit. Reviewing communicable disease reports to local public health agencies and historical summaries of HAI may suggest the need for increased numbers of private rooms for AIIRs. There are major differences across the United States for the types and prevalence of disease requiring ventilation controls, which affect the need for AIIRs or PEs. Budget Issues Healthcare epidemiology and infection control (HEIC) staff participation is critical in the initial planning and approval meetings during the programming or design phase. Issues frequently addressed include budget, space constraints including storage and equipment cleaning areas, air handling units, hand washing facilities, appropriate finishes, specific products with infectious implications, and applicable regulations. HEIC staff should be prepared to support their position and recommendations with published citations whenever feasible, especially when a recommendation is not budget neutral (8, 9, 64, 86). HEIC staff frequently work with consultants during the planning phase of specific projects, including architectural and construction companies in a “partnering” process. Consulting an environmental expert might also be necessary if the size and complexity of construction provides considerable risk to highly susceptible patients because of location, prolonged time of construction, work conducted over continuous shifts, and likelihood of air handlers sustaining frequent interruptions. These variables increase risks to patients and personnel and may require environmental testing. If appropriate, budgets for environmental consultants and anticipated testing or environmental monitoring must be considered at the earliest stage of planning. Major design components that must be addressed include design to support IC practice and design and number and type of isolation rooms (i.e., AIIR or PE). Special Environments—AIIR and PE New Construction or Renovation AIA/FGI guidelines outline the design characteristics for AIIR, including no minimum requirement for anterooms. Anterooms may be useful for supplies and accommodating personal protection equipment but are not needed to maintain negative air pressure of the room with respect to the adjacent corridor. The guidelines do not support dual-purpose positive and negative ventilation (i.e., rooms “switched” from negative to positive air pressure) because of concerns over reliability and maintenance of intended pressurization relationships. AIIR in new construction or renovation require a negative airflow of at least 12 air exchanges/hour (ACH). Although audible alarms may be used to monitor AIIR, current guidelines for new construction require permanently installed visual mechanisms to constantly monitor the direction of airflow (4). AIIRs also require self-closing doors and tight sealing of the room. If the air cannot be exhausted directly to the outside, it must be filtered through HEPA filters before it is recirculated to the facility's HVAC system. PEs are not required by the guidelines because they are dependent on the program of the organization. However, the guidelines appendix provides suggestions for PE design (4). These designs are consistent with CDC guidelines regarding tuberculosis and pneumonia (5, 161). Planning for a population needing PE should consider the one condition that requires an anteroom to achieve proper airflow (i.e., a highly immunosuppressed patient who is infected with an airborne infectious agent like VZV requires positive pressure in the room to protect from other airborne infectious agents like Aspergillus and also requires removal of the air to ensure protection of caregivers from VZV). The guidelines offer two designs to accomplish the pressure relationships, both requiring an anteroom. Ventilation and Mechanical Systems and Basic Infrastructure Long-range planning requires attention to key systems such as HVAC, including recommended ventilation and filtration specifications and mechanical systems involving water supply and plumbing. Key parameters for HVAC include filtration efficiency, air exchanges, pressurization relationships, humidity, and temperature. Recommended ranges for each of these are outlined in detail in the guidelines and elsewhere in this text (4) (see Chapter 89). Rooms and Storage Supporting Infection Control Practice The guidelines require specific areas such as utility rooms (soiled and clean), instrument processing, holding, and work P.1559 rooms. Storage of movable and modular equipment is critical from both a life safety and cleanliness viewpoint. The public perception of clutter is frequently associated with contamination and is seen as an IC problem. Stretchers, wheelchairs, intravenous (IV) poles, and other large patient care equipment are generally shared among units. Adequate space is needed to store, remove, clean, and maintain the items in an orderly fashion and reduce damage to surfaces and must be located away from normal traffic (4). In addition CMS and state-based enforcement agencies emphasize clear, unobstructed corridors in healthcare facilities. Design and Surfaces Ideally, surfaces are designed to include cleanability; problems can be avoided if surfaces near plumbing fixtures are smooth, nonporous, and water resistant. Operating and delivery rooms and isolation and sterile processing areas also need smooth finishes that are free of fissures or open joints and crevices that retain or permit passage of dirt particles (4, 170, 173). Planning may include consideration of light fixtures that have flat surfaces for ease in wiping clean. Window ledges are dust-collecting horizontal spaces that can be eliminated with a minimum width of nonporous material. Seamless, sealed floors are required to be clean not waxed and having rounded corners and edges aids in reducing the accumulation of debris from traffic, fluids, and dirt. Noncloth furniture resists absorption of moisture and stains, making cleaning more effective and efficient. Stainless steel surfaces, in particular, are both resilient and easily sanitized. Selection of surface materials, therefore, must balance use life, cleanability, cost, and maintenance. Selection of Building Materials The construction materials vary for flooring (identify precise location of carpet or vinyl); walls; headwall components; windows; doors; countertops; plumbing fixtures (i.e., sinks, faucets, handles, etc.); lighting; electrical outlets; furnishings (e.g., bed, chairs, bedside tables); and computers, equipment, and supplies storage areas. Choices should consider selection of latex-free construction materials for all items, sizes, dimensions, colors, finishes, securement, and seams. Counter space required for various activities should have countertops that are seamless, nonporous, and durable against multiple germicidal cleanings. IC aspects associated with construction materials must be included along with those of local fire marshal requirements and state and local mandated codes and standards. General IC considerations include nonporous surfaces that are easily cleaned with Environmental Protection Agency (EPA) registered germicides. They should also consider hands-free, foot pedal, or sensor-activated faucets; lids; handles; dispensers; and controls to the extent feasible. HEIC staff should evaluate materials that withstand harsh chemical contact without corrosion, staining, or disruption of function and durability. Modifications that reduce soil and debris reservoirs include seamless design, rounded corners, sealed seams, wall bumpers, handrails, and electronic door openers. Counter space required for various activities should have countertops that are seamless, nonporous, and durable against multiple germicidal cleanings. Drawers and containers for storage should be constructed from seamless, molded materials with rounded corners to prevent cracks, crevices, or folded edges that attract soil and are difficult to clean (150, 174). Furnishings, Fixtures, and Equipment Furniture Modular furniture not easily moved should be installed on raised platforms or suspended in some manner to achieve a minimum 6-in. to 12-in. clearance from the floor to allow pull out for cleaning or to allow cleaning underneath. Attention must be paid to storage units with electrical or computer connections. Upholstered furniture should be managed like carpeting (including disposal) in the event of major soaking and contamination as a result of floods, leaks, or sewage. If furniture is affected by only steam moisture, it can be dried. Hardwood with intact laminate can be cleaned and disinfected with dilute bleach. Laminated furniture that has exposed particle board beneath the surface or other furniture composed of pressed wood or chipboard supports fungal contamination and growth when wet and should be discarded if it becomes soaked (9, 64). Hand Washing Stations and Hand Cleaning Agent Dispenser Placement Design and placement of hand washing stations becomes more critical with the additional consideration of waterless alcohol-based hand rubs and has an impact in the event of plumbing disruptions or lack of preventive maintenance. Number and Design. The guidelines for new construction recommend the minimum number of hand washing facilities for hospital patient rooms as one in the toilet room and one in the patient room outside of the privacy curtain to ensure that HCP can carry out standard precautions. Having a sink in a patient or resident room and in the toilet room supports essential IC practices. IC plays a critical role in recommending proper placement of hand wash facilities. In addition, IC support for a sink standard of minimum dimensions may prevent installation of small “cup” sinks that challenge proper hand washing (170). The guidelines describe permissible types of controls for hand washing facilities in various areas. Placement. Improper placement can add to the environmental reservoir of contaminants. Sinks must be convenient and accessible, but nearby surfaces should also be nonporous to resist fungal growth (64, 170). One source recommends a minimum distance of 15 ft from all inpatient beds or bassinets and 25 ft from outpatient chairs, stretcher, and treatment areas to ensure access (170). Hand washing facilities should also be situated to avoid splashing (suggesting at least 36 in. from patients or clean supplies) or equipped with a splash guard to avoid splash contamination (170). CDC hand hygiene guidelines (175) make a strong recommendation for addition of waterless alcohol-based hand antiseptic agents as part of a facility's overall hand hygiene program. Dispenser location has emerged as one of the critical issues to address for this class of products. For example the CDC P.1560 guideline recommends that these not be placed near the hand washing stations to reduce confusion between them and antimicrobial soap used with water. Since the publication of these guidelines, there has been an increase in the adoption of waterless alcohol-based hand antiseptics by U.S. healthcare facilities. Theoretical concern of flammability of this class of hand hygiene agents has prompted fire safety officials in several states to restrict location of dispensers to patient care rooms or suites and prohibit them in exit or egress corridors (176). Perceptions that waterless hand hygiene products will supplant the need for hand washing stations also are unfounded. Both traditional washing with soap and water and the waterless products are needed, and the ICRA process should ensure adequate provision for new construction and renovation. Cabinets. Areas beneath sinks should not be considered storage areas because of proximity to sanitary sewer connections and risk of leaks or water damage. Clean or sterile patient items should be not be placed beneath sanitary sewer pipe connections or stored with soiled items; cleaning materials are the only items acceptable to be stored under sinks, from a regulatory aspect (170). Facilities may develop design standards excluding storage space beneath sinks, thus preventing misuse and need for cleaning. As noted earlier, cabinet construction materials need to be nonporous to resist fungal growth. Aerators. Aerated sink faucets located near patients, particularly in ICUs, may be a risk because of their ability to enhance growth of water-borne microorganisms. The faucet aerator has been identified as a reservoir and possible source of infection within the hospital. Rutala (177) noted that the most convincing evidence for the role of faucet aerators is provided by Fierer et al. In this study, premature infants became infected with Pseudomonas aeruginosa from delivery room resuscitation equipment contaminated by a faucet aerator. Rutala concluded that the degree of importance of aerators as reservoirs for nosocomial pathogens remains unknown. Because Legionella species grow well in the sediment formed in aerators, Freije et al. (135) recommend aerator removal. Proper sink design and dimensions can reduce splashing and risks of general contamination, while eliminating concerns for aerators completely. Flush Sinks and Hoppers Clinical sinks are frequently located in soiled utility rooms for disposal of body fluids and liquids but warrant similar considerations for moisture and contamination. Clinical or “flushing rim” sinks remove contaminated fluids in a manner similar to toilets and are not intended as utility or instrument cleaning sinks. Splashguards are valuable but inclusion may depend on sink design and use. If staff members are not routinely required to use face protectors, a splashguard should be required. Whirlpool and Spa-like Bathing Facilities Various types of bathing facilities are now available for mothers in birthing rooms and as additional amenity for some patient care rooms. Recommendations for cleaning have been compared with hydrotherapy tanks and equipment cleaning procedures (9). However, plumbing for a traditional whirlpool bath circulates water through piping and jets that are inaccessible to mechanical cleaning. Potential risks for cross-transmission of contaminants is, therefore, possible, especially if used during labor given the likelihood of introducing blood or other body fluids, which can be trapped in the pipe system. Pipeless whirlpool baths are commercially available, and cleanability using an in vitro testing protocol has been verified by the National Sanitation Foundation (Sanijet Corp., Coppell, TX; http://www.sanijet.com). Controlled trials comparing traditional to pipeless whirlpool baths are lacking, and the evidence demonstrating disease transmission from these systems is anecdotal. Communication with state regulators, cleaning and disinfecting the tub and jets with specific spa-cleaning products, and proper draining and flushing sequences are essential when considering installation (9). Eyewash Stations OSHA directs proper use and placement of eyewash stations with distance determined by the pH of the involved chemicals. Source water in stationary eyewash stations may stand unused in the incoming pipes at room temperature for long periods, providing a reservoir for potential pathogens (177). After a report of Acanthamoeba in eyewash stations, OSHA issued a bulletin recommending cleaning and disinfection methods. The schedule follows the American National Standards Institute Z358-1981 recommendations for flushing the system 3 minutes each week (120). Dispenser Placement—Sharps Containers Location of disposal containers should consider ease of visibility to avoid overfilling and should be within easy horizontal reach of the user. Systems should have secure locking and enable easy replacement. When containers are fixed to a wall, the vertical height should allow the worker to view the opening or access the container. NIOSH recommendations suggest ergonomic considerations for installation heights or creative approaches for specialty areas (168). Sufficient temporary storage space for filled containers must be in design planning (166). If a mobile cart mechanism is used, construction materials for the carts and containers must be fluid resistant, have appropriate biohazard signage, be puncture proof, and have a secure closure (166). Sharps containers and needle boxes are currently wall mounted in close proximity to the point of use; the containers are usually replaced when two-thirds full (168). Location, placement on the wall, and so forth must consider use such as residents' needs for medication, the main medication preparation area, and treatment rooms. Although this may be addressed in furnishings, it is appropriate to consider it with waste management. CMS also addresses proper storage and containment of waste in dumpsters and the management of the loading dock (e.g., free of debris and covered receptacles) (158). Ice Machines Ice availability for human consumption and medical nursing treatment may be located in the nutritional area or a clean room. Because contamination frequently occurs with ice because of inadequate machine maintenance or contamination during collection and handling of ice, an ice delivery method should be designed to minimize contamination. When icemaking equip P.1561 ment is accessible to patients or visitors it should be self-dispensing to avoid touch contamination. The ICP should ensure that the ice machine is designed to deliver ice without permitting the receptacle and human hands from coming in contact with the dispensing port. The drainage tray should permit routine cleaning and disinfection and eliminate any standing water source. Direct access and storage bins with ice scoops should be avoided (178). If a wall collection and removal system is planned, then construction materials and mechanisms would need to address IC aspects of containment and confinement with risk-reduction cleaning capabilities. ICRA for Construction and Renovation Projects—Process Overview A good CRP supports long-range planning as discussed previously and provides guidance for individual construction projects, large or small. An ICRA for a specific construction project ensures appropriate planning for major new construction that also involves excavation and/or demolition or basic steps for simpler renovation projects. The ICRA team reviews the plan with considerable attention to detail by making inquiries to clarify understanding before a sign-off is completed. HEIC staff assess the plans, paying particular attention to the specific requirements cited for the building improvement. HEIC staff should focus on both the general and specific design aspects that influence and/or impact desired IC practices. If IC input does not occur in the beginning phase, there may be problems later with the infrastructure systems, such as air, water, traffic, and disruptions that impact on residents. For example, air quality may be compromised because of infrequent filter changes, leading to aerosolized fungi released from dust during the demolition phase (8, 9) (see Chapter 89). Water may become contaminated with microbes when numerous dead-end pipe junctions contain stagnant water or when old piping is disrupted in replacement phases. Problems also occur when chlorine and/or temperature interventions to control Legionella are not maintained. A recent report documents that plumbing in even newly constructed nursing homes was readily colonized with Legionella (108). Patients The ICRA team assesses the inherent susceptibility of the patient (e.g., degree of immunosuppression as in a bone marrow transplant patient) and the risk associated with the degree of invasiveness for procedures (e.g., patient undergoing surgery). The degree of dust and moisture is also assessed according to the size of the project, the length of time of the project, and the frequency of shift. After the assessment is made, a determination of the impact on the populations and the impact on areas adjacent to the construction site is made. Fig. 88.1 describes one widely used process using a matrix that matches levels of patient risk with levels of anticipated construction dust. Figure 88.1. Infection Control Risk Assessment Matrix of Precautions for Construction and Renovation and Infection Control Construction Permit. (Forms modified and provided courtesy of J Bartley, ECSI Inc, Beverly Hills, MI 2002. Steps 1 to 3 adapted with permission from Kennedy V, Barnard B, St Luke's Episcopal Hospital, Houston TX; and Fine C, CA; Steps 4 to 14 adapted with permission from Fairview University Medical Center, Minneapolis MN.) The risk score determines needed interventions based on the following: Construction activity—project complexity in terms of dust generation and duration of activity Patients—assessment of the population at risk and location in terms of invasive procedures The matrix grid format immediately leads to identifying the following: Number and types of necessary controls and IC interventions Signatures of all parties, thus providing accountability for the mutually agreed on plan (9, 171) The process is made efficient by incorporating the precautions that can be determined using a decision-support matrix and a checklist in the form of a permit with signatures. Submission of an IC permit is an additional step and a useful method that is designed to assess the complexity of the project as a matrix of risk groups (patients and environment) (Fig. 88.1). The precautions, internal and/or external, include determining appropriate protection of occupants from demolition, ventilation and water management following planned or unplanned power outages, movement of debris, traffic flow, cleanup, and acceptance of the final renovation from the constructor. Whether or not this matrix method is used, there are key issues that should still occur: Routine submission of scheduled project lists from facility management to IC, enabling IC to be proactively aware of projects and to anticipate IC needs Submission of an “IC permit” or “project approval signature block” before the beginning of projects, beyond required project lists (9, 171). Formats may range from simple checklists to questionnaires designed to assist staff members in assessing risks and identifying prevention strategies Worker and Contractor Expectations Contracting companies receiving the documentation that describes steps to take to protect patients must also consider management of contractor employees for security and IC purposes. Requirements for contract workers must be spelled out in project manual specifications documents. Expectations include control methods such as badges (pictures), point of entrance or access to the construction site, or entrance to the hospital. Check-in and checkout procedures, specific areas for donning and removing protective garb, and eating and toilet facilities should be identified well before the project begins. Health requirements and educational issues vary by project but should be included in principle as items that must be determined by mutual agreement between the owner (healthcare organization) and the construction company or companies. Obtaining the cooperation of contractors is key to ensure that the hired work crew observes appropriate behavior when entering a hospital site. Provision of training and education by ICPs and healthcare professionals to contractors and subcontractors is the first step in creating a stronger sense of partnership. Training should include information on hygiene, traffic patterns, availability of protective wear (e.g., shoe covers and cover gowns), and other dust containment recommendations. Tendering documents should include all expected necessary containment recommendations. These recommendations may include that dust on clothing and boots be removed before entering the healthcare facility; that entrance to high-risk patient and staff P.1562 P.1563 P.1564 P.1565 P.1566 P.1567 traffic areas be avoided; that cover gowns and booties be made available for workers; and that workers be provided with portable toilets for their use only and with potable water to wash, preferably outside of occupied healthcare facility grounds. These precautions help limit the amount of dust that is introduced into the healthcare facility. A partnership with contractors helps ensure greater respect for IC concerns among construction workers and raise the level of IC awareness regarding the different phases of the project, particularly high dust-generating activities (e.g., demolition of a targeted building) (67). Select aspects that should be in place for contractors and subcontractors include the following: Proof of liability and worker's compensation insurance Training on owner (facility) safety and IC policies and any other federal, state, and local authority having jurisdictional requirements Identification of hazardous chemicals planned for use and material safety data sheets (MSDS) provided to owner Spill response plans outlined for hazardous chemicals Personal protective equipment (PPE) available and notice of anticipated generation of hazardous waste Location and access to owner emergency care services Assessment and documentation of interim life safety measures (ILSM) Evacuation and fire safety response plans confirmed Plans for worksite dust containment reinforced and attention to wall or floor penetrations PRECONSTRUCTION Project Management ICRA Team Sets the Stage Worker Risk Assessment and Education Health, Training, and Education Health risk evaluations for potential exposures depend on the type of construction planned. Facility staff overseeing or working with outside contractors should assist in determining potential environmental risks for facility workers or contractors. Policies should include provisions for training and by whom (facility or contractor). Training must be appropriate to the task (e.g., staff entering air systems for preventive maintenance, such as changing filters, should be alerted to the potential for airborne dust containing spores of microorganisms and arrange to first turn off fans and don a mask). Staff members working in sanitary or septic sewage systems, drainage pipes, and so forth should be alerted to the risks of moisture and fungal contamination (8, 9, 82, 161, 163, 177). Agreements should be developed appropriate to the project regarding provisions for pertinent health protection, vaccinations, tuberculosis assessment and purified protein derivative (PPD) skin testing, or related education before workers begin construction. Requirements vary with degree of environmental risk and proximity to the patient population. As agreements are completed, they should provide evidence that workers have received appropriate health protection as noted previously and should include the following information: Facility exposure control plan(s) for IC, hazardous chemicals, and life safety How to seek help and report exposures (e.g., first-aid location and initial steps to report exposures) Use of particulate respirators or other PPE Risk prevention for unexpected safety issues, such as noxious fumes, asbestos, and so forth (9, 161, 162, 163, 164) (see Chapter 89) The facility should be satisfied that provisions have been made for effective IC education designed to address facility-specific needs related to potential infectious risk exposures as described previously (9, 160, 161, 162, 163, 164) Preparation for Demolition and Construction The project teams provide ongoing planning and monitoring during area preparation and throughout the demolition, construction, cleanup, preparation for return to service, and final project review (4, 8,159). Before construction begins, the focus of preparations should be on isolation of the construction or renovation area. Some sources categorize projects in terms of minor or major risk based on the level of needed barriers; checklists are developed accordingly (9, 64). External Excavation Precautions External excavation is ideally conducted during off-hours so that air handlers can be adjusted; the goal is to protect the intake as much as possible. Small projects require similar planning and vary by degree, but preparation still requires early communication with facility management. Specific educational needs (e.g., OSHA), regulations, and health issues for patients and workers need to be addressed. A final customized checklist should be appended to the CRP (9). Inspection of the Worksite Daily inspections should be made, particularly at the start of a project. Recording inspections and observations is recommended. The inspection should look at major areas, including the following: Dust containment barriers at the source are appropriate The frequency in wetting excavated soil or demolished building, truck, and equipment path is adequate Doors, windows, and other ports of entry located near the project are sealed or barred from use Construction worker behavior, such as removing dust and observing good hygiene before entering into health care grounds, is acceptable Waste is kept to a minimum It is recommended that an inspection worksheet or checklist be created, with daily inspections and observations recorded and copies given to the designated individuals who can correct the situation when necessary. The worksheet should include key precautions to observe and a follow-up segment. These worksheets act as a means of communication, and, if a problem arises, they become evidence that due diligence was exercised by ICPs and other healthcare professionals (67). P.1568 Internal Issues Type and Extent of Construction Project complexity varies with time, numbers of workers, whether contractors work continuous shifts, scope and degree of activity (high or low dust generation), and proximity to patients with varying degrees of risk for infection. Internal Renovations Internal projects require much additional planning, compared to external construction. Patient areas or units that cannot be closed or that are adjacent to a major renovation require special planning (e.g., OR additions adjacent to an active surgical suite). These situations may justify environmental monitoring beyond visual inspection to detect increased airborne contamination and to plan interventions (5, 8, 9, 18, 24, 82, 160). General Issues Patient Location during Construction There should be no flow-through traffic in the area, meaning routing patterns for staff traffic and visitor access traffic must be planned and designated, and signage must be posted for ease in compliance. Adherence to existing codes and standards for the size of corridors and doorways remains in effect. Visitors or residents investigating progress during construction may place themselves and construction workers at risk. This requires considerable monitoring by staff to ensure a safe environment surrounding the renovation and/or construction. Risk Factors Managing infectious risks during construction means collaboration among all personnel. These risks include dust and debris compromising the environment, airborne microbes carried to immunocompromised residents, an unbalanced ventilation system affecting air quality, water contamination, accumulated and multiple waste reservoirs, ineffective dustproof barriers, to name a few. Depending on the location of the construction and the proximity to resident care areas, residents may have to be relocated to a safer unit. Meticulous maintenance of physical barriers and infrastructure systems (i.e., air, water, etc.) are required as risk reduction efforts. Airborne debris of particulate matter may carry microbes that contaminate the air and are especially hazardous to residents who may inhale the debris and develop respiratory infections and/or complications. Control of airflow patterns (e.g., clean to dirty); interruption of utility, building, and equipment services; and communication requirements should be specified in the project bid proposal to ensure construction specification compliance. Environmental Control and Containment Containment Isolating the construction site by physical dust control partitions requires floor to deck (solid compartment separation between floors above dropped ceiling) walls made of airtight fire-rated barriers, usually consisting of drywall or plywood with caulked seams or heavy duty plastic with sealed seams and gasketed door frames. Site access points are controlled entries for those authorized to enter. These egress paths are located where minimal debris can be transferred from the construction side to the cleaner areas of the facility. Personnel authorized for entry are commonly identified by badge and protective gear, such as hard hats. Emphasis is placed on dust control, which is a constant challenge during the project; diligent cleaning efforts are critical. Dust collection mats with adhesive surface can also assist with minimizing migration of dust and debris carried by construction personnel. These mats typically have several layers that can be removed as needed when the exposed surface becomes loaded with dust. Daily cleaning by gathering gross debris for disposal is necessary before damp mopping the area as a dust control mechanism. Containment is further practiced when a debris exit path is marked and a delivery point of materials and supplies is designated. Containment also includes HVAC systems. Measures such as sealing of grills or vents against construction debris; frequent changing of filters within the ventilation ducts; ensuring that the window seals are leak proof and airtight; and, if chutes are used to remove demolition materials, monitoring for negative pressure and ensuring that the chutes are closed when nonoperational or during duct cleaning are all important aspects to address. During construction, unintentional water contamination of porous, acoustical ceiling tiles and/or fireproofing and filter materials may occur. Prompt removal of damaged, moisture-laden materials reduces the potential for fungal spore release (9, 160, 173). Dust and Debris Control—Barrier Systems. The area should be isolated, as the project requires. Small, short duration projects generating minimal dust may use fire-rated plastic sheeting but should be sealed at full ceiling height with at least 2-foot overlapping flaps for access to entry. Any project that produces moderate to high levels of dust requires rigid, dust-proof, and fire-rated barrier walls (e.g., drywall) with caulked seams for a tight seal. Large, dusty projects need an entry vestibule for clothing changes and tool storage. The entry area should have gasketed door frames; tight seals should be maintained at the full perimeter of walls and wall penetrations. An interim plastic dust barrier may be required to protect the area while the rigid impervious barrier is being constructed. Cleaning is required at completion of the barrier construction; plans should also describe a terminal barrier removal process that minimizes dust dispersal (9, 64). Ventilation. Air System Flow. It should be determined whether the construction area uses fresh (outside) or recirculated air; filters should be added or return vents covered as needed with filter material or plastic. Air must flow from clean to dirty areas (4, 8, 9) (see Chapter 89). Negative Air Pressure. The air within the construction area must be negative with respect to surrounding areas and with no dis P.1569 ruption of air systems of adjacent areas. Constant negative pressure within the zone should be monitored with an alarmed device, which must be maintained and monitored by construction personnel. Exhaust from construction air should be directed outside or exhaust vents in the construction area should be sealed to prevent recirculation if possible. If the exhaust must tie into a recirculated air system, a prefilter and high-efficiency filter (95%) should be used before exhaust to prevent contamination of the ducts. Fans should be turned off before opening ductwork, and necessary interruptions (e.g., fire drills) should be planned for to minimize risk (4, 9, 64). Portable HEPA filtration devices can also aid in capture of particulates that might be aerosolized during demolition of drywall, removal of flooring materials, and so forth. Such devices can also facilitate creation of negative pressure by adding a flexible duct from the exhaust pathway of the portable device directly outside, if feasible. Other variables to address include the following: The status of sealed penetrations and intact ceilings should be verified in adjacent areas. Air exchange rates and pressure relationships: It should be verified that the facility can maintain proper rates in critical areas near construction activity, ensure air is not being recirculated without filtration from the construction area elsewhere, and provide accountability for and frequency of testing air pressures throughout the project (8, 9, 64). Vibration or disturbances: Drilling and other sources of vibration have potential to dislodge dust collected above suspended or false ceilings; vibrations loosen corrosion within water pipes as well. Plans should require vacuuming of affected areas and flushing debris from water systems before reoccupancy (8, 24, 115, 135). Specification of temperature and humidity ranges: Determine limits as appropriate (4, 9, 86, 158). Monitoring: Consideration must include risks of malfunction or complete loss of utilities. Both visual cues and particulate air monitoring may be used. The type and frequency of monitoring, evaluation of results, and follow-up action by designated parties are essential to planning (8, 9, 64). Traffic Control Control The safety approach to traffic control is signage that identifies construction areas and restricts entry to authorized construction personnel who have appropriate protective equipment. The IC perspective is to divert nonessential traffic (e.g., patients, HCP, or visitors) from the site, thereby reducing risk of exposure to or dissemination of airborne pathogens carried by dust. If intersection of patient care areas and construction is unavoidable, the route should be designed to minimize risks of exposure to infectious agents even if they have donned personal protective attire (masks). Visitors are guided to the most direct but safest route to visit residents. Because visitors are potential reservoirs of infectious agents transmissible to susceptible residents, they should be assessed for symptoms of communicable infectious diseases whether construction projects are in progress or not. Designated entry and exit procedures must be defined. Egress paths should be free of debris, designated elevators should be used during scheduled times, and only authorized personnel should be allowed to enter the construction zone. Signage should direct pedestrian traffic away from the construction area and materials (8, 9, 24, 64). Debris Management: Windows, Chutes Debris. Used materials should be removed in carts with tightly fitted covers, using designated traffic routes. Medical waste containers (sharps or other medical regulated waste) should be removed by the facility before start of the project. Efforts should be made to minimize use of elevators with transport during the lowest period of activity. Debris should be removed daily and at times specified by agreements. If chutes are used to direct debris outside, HEPA-filtered negative air machines should be used, and the chute opening should be sealed when not in use. Filters should be bagged and sealed before being transported out of the construction area (8, 9, 24, 64). Exterior Windows. Windows should be sealed to minimize infiltration from excavation debris. Patient Equipment—Contamination of Patient Rooms, Supplies, and Equipment Worksite Garb Contractor personnel clothing should be free of loose soil and debris before leaving the construction area. If protective apparel is not worn, a HEPA-filtered vacuum should be used to remove dust from clothing before leaving the barricade. PPE (e.g., face shields, gloves, respirators) is worn as appropriate. Contractors entering invasive procedure areas should be provided with disposable jump suits and head and shoe coverings. Protective clothing should be removed before exiting the work area. Tools and equipment should be damp wiped before entry and exit from the work areas (8, 9, 64). Barriers Areas around construction should be monitored to maintain protection of in-use patient care areas as described. Patient doors adjacent to construction area should be kept closed, with appropriate traffic control (8, 9). Storage Sites should be designated for new and damaged construction materials (9). Contractor Cleaning The construction zone should be maintained in a clean manner by contractors and swept or HEPA-vacuumed daily or more frequently as needed to minimize dust. Adjacent areas should be damp mopped daily or more frequently as needed. Walk-off mats may minimize tracking of heavy dirt and dust from construction areas (8, 9). Facility Cleaning Contracts should clearly specify responsibilities and expectations for routine and terminal cleaning before opening the newly renovated or construction zone (8, 9). P.1570 Site Cleanliness Monitoring the area proximal to the barriers surrounding the project site is usually delegated to the housekeeping and support service. Frequent cleaning is basic to maintaining dust control. Project site cleaning is an ongoing activity that should be viewed as a critical success factor in reducing risk. A question may be raised concerning the need for air testing of particulate matter to determine site cleanliness. A more productive approach is a preventive one, that is, establish routine cleaning frequencies at the same rate that a facility might institute if air testing demonstrated that dust levels were high. The IC and safety aspects of maintaining a clean work area include reduced clutter and fall hazards, diminished exposure to airborne debris that may cause infectious or allergic responses, and enhanced visibility to perform the work at hand. CMS is also concerned with providing an environment that is free from hazards (e.g., wet floors not identified with signage or blocked access) (158). Similar concerns arise throughout construction or renovation projects and require vigilance on everyone's part to maintain safety and control dust. Standard housekeeping IC practices are followed. Housekeeping equipment should be designated for this area. Fresh germicidal solutions are used and changed often. Chemically treated dust cloths and mop heads should not be shaken and are laundered daily. Vacuum and suction machines are equipped with high-efficiency filters and changed frequently for maximum benefit in controlling airborne dispersal of dust and microorganisms. Frequency of filter changes is workload dependent and based on filter efficiency and performance effectiveness. INTRACONSTRUCTION PHASE AND THE ROLE OF A HOSPITAL EPIDEMIOLOGY AND INFECTION CONTROL PROGRAM Communication Once renovation or construction has begun, the ICP should be available to provide maintenance and operational input. Frequency of input or meetings depends on the scope of the project. Specific concerns must be customized in each project and include IC practices, education, and monitoring. The ICP is vital in educating and supporting “users or owners” to manage their area under construction (e.g., educating staff members on how to monitor their own performance as much as possible). In more complex projects, the ICP may assist directly or make provisions for items already outlined. A number of areas involving specific ICP involvement are discussed later. Environmental Rounds An efficient method to integrate key IC and life safety issues is the use of rounds, using simple checklists based on the items addressed previously (171). ICPs can advise or participate in rounds, which should be scheduled as often as necessary and include a variety of observable “indicators” such as barriers (doors, signage), air handling (windows closed), project area (debris, cleaning), traffic control, and dress code. It may be necessary on occasion to schedule rounds after normal hours or on weekends if that is when construction or renovation is scheduled (8, 9, 64). Environmental Monitoring Activities during Construction There are currently no recommendations for routine environmental culturing during construction. Enhanced targeted patient surveillance (e.g., respiratory illnesses consistent with aspergillosis or legionellosis) near construction areas should be part of the ICRA. Other control measures previously discussed must be continuously monitored. However, when an outbreak associated with construction is suspected or identified, water or air sampling may be indicated. It is vitally important to establish a hypothesis with clear and measurable goals. Culturing or sampling procedures should be defined before initiation (e.g., asbestos, fungal, or particulates). Sampling procedures relative to the suspected agent(s) and sources should be used. The investigator must be cognizant of the many pitfalls associated with the interpretation of environmental data. Therefore, as part of the investigation planning, it is important to establish parameters for interpreting collected data. Outcome or Process Measures Projects may be approached as performance improvement initiatives using outcome measures (e.g., SSI rates) or process measures (measuring compliance) using visual observations, airborne particulate monitors, satisfaction surveys, and so forth (9, 18, 160). Impact on Special Areas Patients requiring AIIRs need close monitoring to ensure that negative-pressure relationships are maintained, particularly when there is potential for disruption of pressure relationships (8, 9, 32, 179). Intake areas such as emergency departments need planning to triage potentially infectious patients (4, 5, 160). If highly susceptible patients cannot be relocated, indicators should be identified to trigger planned intervention (8, 9, 18, 24, 64). Immunosuppressed populations in bone marrow transplantation units or protected environments, ICUs, and so forth require special planning. The goal is to minimize patient exposure to major construction activity; therefore, nonemergency admissions should be avoided during periods of major excavation. If delaying admissions is not an option, patients should be located in areas as remote as possible from construction activity (8, 9). Patient Location and Transport Healthcare providers should plan patient care activities to minimize exposure to construction sites. At least one study found that critically ill, ventilator-dependent patients transported from the ICU for diagnostic or therapeutic procedures was an independent risk factor for development of ventilator-associated pneumonia (9). To decrease exposure for patients during construction activities the following should be considered: P.1571 Provide treatment in the patient's room Transport via an alternate route Schedule transport or procedures during periods with minimal construction activity Minimize waiting and procedure times near construction zones Mask patient or provide other barriers (e.g., covering open wounds) based on patient's clinical status Emergent Issues—Interruption of Utility Services Utility services may be interrupted during any type of construction. Infectious agents may contaminate air-handling units, medical vacuum, and water systems after planned or unplanned power disruptions. HEIC can provide input into emergency preparedness to reduce the potential risks of contamination. Response plans should include assessment of the population at risk and cleanup should focus on steps to prevent, detect, and reduce risk from infectious hazards. For example, as power is reestablished after an interruption, dampers and fans of air handling units resume operation. Dust and particulate matter released during this process may transmit allergenic or infectious agents such as Aspergillus species to patients and staff (8, 9, 17, 24, 64, 135). Therefore, IC policies for areas in which invasive procedures are performed should require sufficient time to clear the air of potential contaminants before resuming the room(s) use. Ventilation time should be based on the number of air changes per hour required by the area. The NIOSH chart for removal efficiency of airborne contaminants may provide guidance, but its use should be tempered by its assumptions (5, 160). In the event of major contamination of patient care areas, plans should specify responsibilities for these decisions and for intensified cleaning, environmental surveillance of airborne infectious agents, and restriction of water use until testing or flushing determines safe use. POSTCONSTRUCTION Postconstruction and Cleanup Project Checklists Check-off lists of expected practices identified at the beginning of the project should be reviewed for items agreed on before the area is returned to full service or patient occupancy. A useful tool during review is the contractor's “punchlist” to ensure that missed details have been addressed (e.g., installations of soap dispensers or designated types of hand washing and sink controls) (8, 9, 171). Owner Preinspections before Move-in Suggested check points for inspections include validating air systems by verifying air balances and pressures, checking electrical current of wall outlets, testing suction capability of wall units, assessing oxygen and gas delivery ports for ease in delivery and control accuracy, checking illumination sources, flushing water systems, rechecking that sinks are in place and functioning properly, determining if aerators are absent, testing whether soap and towel dispensers are full and functional and whether sharps containers properly placed. Postconstruction Agreements Cleanup agreements (e.g., cleaning, air balancing, filter changes, flushing of water systems, etc.) and other utility service checks and cleaning must be established in the early planning phase as discussed previously. These include the following at minimum: Contractor cleaning to include area clearance, cleaning, and decontamination and wipedown Cleaning after removal of partitions around construction area, minimizing dust production Facility-based routine and terminal cleaning before returning area to service Provision of time frames for facility review (e.g., 2 weeks) after completion of the project to ensure that all issues were addressed properly Systematic review of outcomes in the facility's designated review process, whether by contract or committee structure. Items may range from sealed cabling and electrical penetrations and ceiling tile replacements to the completed punchlist Cleaning and replacement of filters and other equipment if affected by major or minor disruptions or conditions that could have contaminated the air or water supply (9, 23, 62, 63, 64) Steps before Occupancy Checklists specific to the project should be developed for a walk-through just before occupancy. Core IC issues for inclusion are listed later as applicable. The designated team should do the following: Check that sinks are properly located and functioning Verify that sinks in critical patient care areas have properly functioning fixtures Check for the presence or absence of aerators in these fixtures according to facility policy Test whether soap and towel dispensers are filled and functioning Check whether surfaces in procedure and service areas are appropriate for use (e.g., smooth, nonporous, water-resistant) Verify that air balancing has been completed according to specifications Test whether air flows into negative-pressure rooms or out of positive-pressure rooms In conclusion, the role of HEIC in construction and renovation remains a challenging and exciting one and is the ultimate demonstration of its multidisciplinary nature. 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It is difficult for those who have no personal experience with the purchase, processing, and distribution of medical devices in hospitals to appreciate the magnitude and diversity of this enterprise. These are the “tools of the trade,” tens of thousands of different products, many of which contact or penetrate some part of some patient some time and whose aggregate cost is in the multibillion dollar range. Superficial attempts to classify the medical device world into neat and precise categories usually oversimplify the picture and understate its complexity. Still, one traditional classification has served hospital workers well for nearly a century, their identification as either reusables or disposables. Reusable devices, also called durables, are usually fabricated from metal, glass, rubber, or woven textiles. They are purchased from an original equipment manufacturer (OEM) in “factory release” condition and before use on a patient are inspected, cleaned, wrapped, and sterilized in the hospital's central supply service (CSS). After use on a patient, they are again cleaned, inspected, packaged, and sterilized. Although the initial unit cost might be high, the ultimate cost is considerably reduced after repeated cycles of use and in-house reprocessing. Disposable devices are traditionally constructed from inexpensive, heat-sensitive materials such as plastics. They are purchased from an OEM, factory-sterilized and packaged, ready-for-use. The original cost is usually low enough so that recycling does not make economic sense. They are intended to be used just once and then discarded. If they are designed for direct patient care, they are usually labeled “for single-use only.” After decades of separate but equal coexistence in the hospital, the distinctions between reusables and disposables started to blur. By the middle 1970s, for various economic reasons hospitals were replacing more and more of their traditional durable and reusable devices with the less expensive disposables. At the same time, there was a revolution in medical technology. Almost daily advances and innovations in diagnosis and treatment and the wholesale adoption of these new techniques created an urgent demand for the instruments and devices that enabled the techniques to be performed. The disposable medical device industry happily responded to this need by fabricating many of these relatively complicated and sophisticated devices, using the same kind of nondurable raw materials found in their simpler, traditional disposables. They were considerably more expensive than the latter but for a variety of reasons they were still labeled for single-use only. In the hospital world of the 1970s, discarding anything that could be used again was not acceptable. Moreover, by this time in history, hospitals had significantly improved their sterilizing competence. (See Chapters 74 and 86.) Recycling was an ecologic and economic virtue. All the incentives for recycling disposable medical devices were in place. It soon became a common practice. The same common sense that justified discarding urine collection bags, after a single use, rebelled against discarding, after only one use, expensive sphincterotomes that “have a lot of life left in them.” Then like now, the hospital world was under constant pressure to cut costs of a “runaway” healthcare system. Parenthetically, during the same period of the late 1970s, some hospitals were experiencing some strange infections (see Chapter 47). They were advised to discard perfectly good reusables that had been used on patients exposed to or suffering from the so-called slow viruses (today known as prions), which were surprisingly refractory to the conventional sterilizing treatments of steam, EO, and strong germicides. Thus, disposables were reused and reusables were discarded. A new nomenclature was in order and it evolved. The colloquial term disposable, once descriptive and appropriate (this chapter, in previous editions of the text, was actually titled “Reuse of Disposable Devices”), is considered today somewhat archaic and even pejorative. The new term, adopted by the Center of Devices and Radiological Health (CDRH) of the Food and Drug Administration (FDA) is single-use devices (SUDs) or “medical devices labeled for single-use.” To avoid ambiguity (and the subtle inference that if a device is called disposable it probably is) the terminology in the rest of the chapter conforms to that used by the agency. What defines a SUD or distinguishes it from a reusable? It certainly is not purchase cost or technical complexity. The FDA implies it is the presence or absence of the OEM's label warning against reuse. The hospital uses a more pragmatic definition: if the device, after use, can be returned to a satisfactory state of sterility and function, it can be reused. However, the most important single feature that should distinguish SUDs from reusa P.1536 ble devices is the intent of the OEM (or arguably, lack of intent). Quite simply, if the OEM intends for the device to be reused, it will be specifically designed for that purpose and fabricated from the appropriate durable materials. If, on the other hand, it is intended to be used once and then discarded, this intent will significantly influence the device design and material selection. Two terms, safe and functional, lie at the heart of the SUD reuse controversy. Clinicians all agree that any device that poses a demonstrable risk of infection or malfunction should have no place in the care of humans. Thus, the first and basic question is whether SUDs, recycled after use, are as safe to use and as functionally reliable as the original SUD purchased from the OEM who fabricated it in a facility that was approved by CDRH and that met their rigorous quality assurance (QA) standards. Another point of interest is whether the original SUD is equivalent to the traditional reusable device it is replacing—the one routinely recycled through the CSS. In addition, it would also be interesting to compare the safety and reliability of recycled SUDs to recycled reusables. Only then can one debate disagreements about economic incentives, legal ramifications, ethical issues, and bureaucratic oversight. Finally, one can raise the question about where the reprocessing should be done—in the hospital, in a facility controlled by the OEM, or by so-called third-party reprocessors. The FDA might have preempted all debate. The agency has recently reexamined its regulatory policy and decided to extend the existing SUD manufacturing regulations, which in the past applied only to OEMs, to hospitals and any third parties who reprocess SUDs. There are those who think that this means the end of SUD reuse. Others worry about burgeoning bureaucracy and intrusion of federal government regulators into hospital practice. This chapter reviews some of the more reliable published studies dealing with the risks of reusing SUDs. To provide some perspective, it describes the historical evolution of device processing in hospitals. It reviews the aims and strategies of the recent FDA action. Finally, it discusses some of the nonmedical issues that still fuel the reuse controversy whether or not the FDA actually implements its new regulations and whether or not they succeed in solving the reuse problem. A brief explanation might be in order for essentially ignoring two types of devices commonly included in discussions of SUD reuse: endoscopes and hemodialyzers. They are routinely recycled in hospitals and are relatively difficult to clean and sterilize. Moreover, the former may sometimes have attachments labeled for single-use only. However, the endoscope is basically a durable device sold to the hospital with full intention and knowledge that it will be reused many times and reprocessed either in the hospital or in a commercial facility. The dialyzer was once labeled as a SUD, but today the manufacturer is obligated by the FDA to provide instructions for reprocessing and reusing. HISTORICAL INSIGHTS Medical Devices and Nosocomial Infections Not too long ago humans lived in a world of epidemiologic naivety. The common fomite phobia that prevailed in the Western world since the discovery of bacteria was also shared by hospitals. From the time of Lister until the 1960s, any medical device—durables or single-use—would be among the first suspects in a case of nosocomial infection. If doorknobs, kitchen cutlery, and pencil erasers were considered serious vehicles for disease agent transmission, what was one to think about devices that came into intimate contact with a patient's skin, mucous membranes, blood, and deep tissue? Actually, the suspicions were not groundless, particularly if the devices had previously been used on patients with overt infections or who might have been carriers. Equally as important, hospital sterilizing facilities and skills had not achieved the level expected today. Packaging was primitive, gravity steam autoclaves frequently failed, poststerilization recontamination was not uncommon, and the parameters and protocols of modern QA were still being perfected. Perhaps the first documented case of a nosocomial infection, attributed to a contaminated medical device, was described by Semmelweis (1) more than a century ago. During a postmortem examination of a woman who died from puerperal fever, a student assistant accidentally pricked the finger of the pathology instructor, Jakob Kolletschka, with the dissection knife. Kolletschka, who was Semmelweis's friend and teacher, developed a sore at the puncture site, was hospitalized within a week, and died shortly thereafter with the generalized inflammatory symptoms of puerperal fever. Medicine did not yet know much about microbes or infectious diseases, but Semmelweis intuitively recognized the reservoir of infection (cadaver), the path of transmission (knife), and the portal of entry (puncture wound) for “the cadaverous particles [that] caused his death.” Students of medical history know that this reasoning, although originally rejected, really anticipated many of the modern concepts about antisepsis, asepsis, disinfection, and surgical sterility. For the purpose of this chapter, however, it is cited only to show that nosocomial infections attributed to medical devices long predate the practice of reusing disposables. They even predate the germ theory. After Louis Pasteur, Joseph Lister, and their contemporaries established the etiologic connection between microbes and infectious diseases, the medical world began to focus its attention on the disinfection of devices and materials used in surgery (2). Metal instruments, sponges, and sutures made from silk and catgut were soaked in corrosive and potent chemicals like carbolic acid, sublimate of mercury, and formalin. The number of device-related infections were reduced, but both patients and practitioners experienced irritation and tissue toxicity caused by the disinfectants. The invention of the steam autoclave, about 1890, was the major breakthrough that essentially solved both problems associated with medical and surgical devices—the risk of infections and chemical toxicity. Most of these devices and materials, at least the critical ones that would contact the very susceptible interior tissues of the body or would be used for parenteral and vascular injections, were made from glass, metal, rubber, cotton, or wool. They could be cleaned and wrapped and then sterilized by steam. After removal from the autoclave, they would remain wrapped and sterile and unexposed to any P.1537 contaminating sources until opened by the physician just before use. Evolution of Hospital In-house Sterilization Thus began the remarkable hospital cottage industry known as the central sterilization department (CSD), central sterile supply, supply processing and distribution (SPD), or any of the dozens of other terms used to describe the same generic task. For nearly a century, these enterprises have been recycling used devices and instruments, originally only from surgery and then from all over the hospital, for safe and efficient reuse. The steam autoclave, the mainstay of the CSS for nearly a century, was joined in the 1970s by EO sterilizers—the gas autoclave. The combination of both systems permitted the hospital to sterilize nearly anything it wanted to, including heat-sensitive materials such as plastics, electronics, optical systems, batteries, and motors—all of which would have been destroyed by the moisture, heat, and pressure of the steam autoclave. In recent years, more sophisticated sterilization systems, including vapor phase hydrogen peroxide and plasma gas, have been introduced to treat heat-labile devices and instruments in the hospital (see Chapter 86). Considering the epidemiologic potential, remarkably few nosocomial infections can be attributed to medical devices sterilized in the modern hospital CSS. This is ample empirical evidence that the sterilizers in use today are reliable and that the hospital reprocessing system works. The used devices are decontaminated, cleaned, and inspected by personnel specially trained for the task. The packs containing the devices to be sterilized are assembled, wrapped, and positioned in the autoclaves according to rigorous protocols. Vacuum pumps remove any air that would prevent penetration of the sterilizing gas. Chemical indicators sensitive to heat or EO are placed in every pack to verify that the contents are actually exposed to the desired sterilizing conditions. The steam and gas autoclaves used for sterilizing are designed for overkill margins of safety to reduce the probability of survival of viable bacterial spores (that are orders of magnitude more resistant than any normal nosocomial pathogen) to less than 1/1,000,000 per pack. The autoclaves are challenged at least once per week with biologic indicators (dried spore suspensions) that monitor their continuing functional reliability. Furthermore, the sterilized packs are stored under strictly controlled environmental conditions until opened and used. (3) In addition to the risk of transmitting infections, users of medical devices face additional problems. Even durable devices wear out and break down; sharps become dull, springs lose their tension, metal rusts. Repeated cleaning and sterilizing cycles accelerated the deterioration. QA programs can be implemented to reduce the number of impaired devices from entering the system, but much depends on the frequency and sophistication of the inspection. Good QA costs money and most middle-sized and small hospitals cannot afford sophisticated QA. However, they can afford the consequences of failure even less. For such institutions, a ready-to-use device whose sterility and function was warranted by an OEM would always be welcome, particularly if it was cheap enough to be discarded after use. SINGLE-USE DEVICES AND THEIR REUSE Hospital Supply Industry and the Plastics Revolution Even during the very early years of in-house sterilization and recycling, hospitals recognized that certain devices and materials, such as surgical dressings, gauze bandages, and catgut sutures, were difficult to reuse. The practice was uneconomical, or inefficient, or, in the case of Listerian dressings—cloth plastered with pitch, paraffin, and carbolic acid—simply too messy. The manufacture of these items was, consequently, relegated to an embryonic hospital supply industry, and the concept of the prepackaged, presterilized disposable, today known as a SUD, was born (4). These two sterilizing enterprises—the hospital's recycling program for reusables and industry's production of SUDs—enjoyed a somewhat symbiotic relationship for close to 50 years until the end of World War II when the plastics revolution swept the country. It was quickly evident that many items recycled by the hospital (e.g., gloves, tubing, syringes, bedpans, dishes, bottles, and linens) formerly made from durable metal, glass, rubber, and woven textiles could now be made much cheaper from the abundant variety of new plastics and synthetic compounds that were being developed and introduced at an unprecedented rate, and these devices were truly disposable. They were fabricated from heat-sensitive materials that would disintegrate in the hospital's steam autoclave, which was the only sterilizing system universally available until the early 1970s. No one wanted to reuse these things anyway; economically, it was not worth the effort. By the middle 1970s, as many as possible of the hospitals' reusable devices, those traditionally recycled in the CSS, were gradually being replaced by presterilized SUDs. Ironically, during these plastics years, the greatest concerns hospitals had about the prepackaged factory-sterilized SUDs were their sterility! With typical professional arrogance, they assumed that only doctors and nurses could properly sterilize medical devices. The sterility concern was resolved after 1976, when the Medical Device Amendments became part of the Food, Drug, and Cosmetics Act. Today, the shoe is on the other foot, and questions are legitimately raised as to whether the in-house hospital sterility standards are as good as those of industry (5). Biotechnology and Medical Devices When the incentives for purchasing SUDs were entirely economic and the SUDs were mostly cheaper replacements for simple items like bedpans and gloves, the only real concerns dealt with inventory management, the space available for storage, and the potential environmental impact of disposing of megatons of refuse (6). The dimensions of the SUD problem changed again during the technology revolution mentioned previously. Hospitals began purchasing an amazing variety of complex gadgetry based on electronic circuitry, membrane technology, expensive optics, and miniaturized components. Today, it is estimated that more than two thirds of the tens of thousands of sterile devices used daily in American hospitals are SUDs. They include the original cheap disposable items and modern arthroscopy instruments, P.1538 laparoscopic dissectors, and endotracheal tubes. Furthermore, the standards of sterility and reliability they must meet are regulated by federal law. Quality Assurance in the SUD Industry The labeling of SUDs for single-use only is, in part, a consequence of the strict testing and manufacturing requirements imposed before the device can be released for sale. The manufacturer must be able to demonstrate both theoretically and empirically to the CDRH that the sterilizing process used is adequate to destroy all resistant contaminants that would be found on the original device and that the probability of contamination on the final product is actually less than one microbe on a million devices. The construction, organization, and sanitary conditions of the manufacturing facilities are regulated by guidelines known as good manufacturing practices (GMPs), and all of this is subject to inspection. Because the manufacturer cannot control any of these manufacturing standards anywhere except in his or her own factory, and one presumes that QA and GMPs are relevant to the safety and effectiveness of the finished device, the manufacturer is protecting himself or herself from liability, as well as protecting the consumer from harm, by warning the world that the product is guaranteed only for the first use. Often overlooked but essential to the understanding of this problem is the well-known fact that cleaning and sterilizing sophisticated medical devices are not always routine procedures, simply accomplished by passing them through a washer followed by an autoclave. The devices must be designed and fabricated with cleaning and sterilizing in mind; concomitantly the recycling process should be designed with the device and its idiosyncrasies in mind (3). Otherwise, the process might fail. The cleaning and sterilizing agents used might not pass through narrow apertures or gain access to all of the critical surfaces or the interior of long narrow lumens, or the chemicals used might corrode or weaken these surfaces. The manufacturers of reusable devices not only design them to be compatible with repeated processing in the hospital's CSS and select fabrication material that can stand up to multiple cycles of use and reprocessing they also provide detailed protocols and instructions to CSS personnel about how to render a used device once again safe and functional. Quite different circumstances prevail in the SUD industry. Here the OEM designs the device to be cleaned, tested, packaged, and sterilized by personnel under his or her supervision and in his or her own facility. Incentives for Reuse It would be reasonable to imagine that the single-use warning label would convince the hospital's management not to recycle a SUD and many hospitals have heeded the warning. Cost-saving imperatives are compelling, however, particularly if the hospital's management is convinced that the enterprise is technically feasible. Most hospitals that are big enough to gain economically from reuse of SUDs have also invested considerable capital in modern sterilizing equipment. They are also the ones that would suffer most from legal and economic sanctions imposed by the community relative to hospital wastes. Moreover, as Mayhall (7) pointed out nearly two decades ago, there are several good reasons for in-house sterilization of SUDs, other than economics. For example, a hospital might want to recycle used SUDs when the delivery of new SUDs has been interrupted, when a package has been opened or damaged and the sterile status of the unused SUD is unknown, or when an unused and presterilized SUD is being incorporated into a new pack that will be sterilized as a unit. A hospital will simply ignore the OEM's warning when the Puritan streak, so deeply ingrained in American hospitals, convinces the hospital that discarding a device is wasteful, expensive, and probably sinful. The attitude of many healthcare professionals was summarized in a succinct declaration at the Association for the Advancement of Medical Instrumentation (AAMI) 1983 conference: “We had not regarded woven catheters as disposable devices. The fact that they are declared disposable means next to nothing” (8). Magnitude of the Reuse Practice No one knows who was the first to resterilize and use again a medical device labeled for single-use only and exactly when it was done. Several lines of evidence point to specialists who were working with expensive SUDs during the early 1970s. At the National Workshop on Reuse of Consumables in Hemodialysis in 1982 and at the AAMI Technology Assessment Conference on the Reuse of Disposables in 1983, the issue came out of the closet and some brave pioneers, particularly in the fields of hemodialysis and cardiac angiography, described their own empirical success with recycling. This should not be surprising. Modern medicine is the home of innovation and “stretching the envelope.” What is surprising is the speed with which SUD reuse swept through the hospital world and its acceptance as a routine, even unquestionable practice. At the 1984 Georgetown University Conference, an informal survey of 204 respondents revealed that 82% were aware of the reuse of one or more types of SUDs in their own institutions. Only 6% stated that their facilities either had a policy prohibiting reuse or did not reuse SUDs; 12% were either unaware of reuse in their institution or did not answer the question (9). At this conference, the FDA cited surveys that showed that in 14% of hospitals were reusing at least selected SUDs in 1976 and that this number increased to 90% by 1982 (10). Also at this conference, the Centers for Disease Control and Prevention (CDC) described the growth of the common practice of reusing hemodialyzers in dialysis centers. During the period 1976 to 1980, 17% to 18% of the centers were reusing. In 1982, this proportion increased to 43%, and it was anticipated that this would rise to 60% by 1983. In the early 1980s, 52% of patients undergoing dialysis in centers reimbursed by the Health Care Financing Administration were in reuse programs (11). In the Georgetown informal survey, the most common SUDs reused were hemodialyzers (46% of respondents), cardiovascular catheters and guidewires (31%), respiratory therapy breathing circuits (18%), biopsy needles (17%), cautery devices (16%), anesthesia breathing circuits (14%), and endotracheal tubes (10%). Of the respondents, 5% to 10% indicated that they reused suture staple removers, syringes, orthopedic appliances, suction canisters, tracheal tubes, and Bovie cords. These were P.1539 followed by a list of 31 devices, the reuse of which was reported by less than 5% of the respondents (9). Reuse in Canadian Hospitals A survey of 1,238 Canadian hospitals (1,065 responded) in 1986 is probably the most reliable and certainly the most comprehensive report on the prevalence of SUD reuse during those years. It revealed that, among the larger hospitals (more than 200 beds), 86% regularly and 6% occasionally reused single-use medical devices; only 8% never reused. Among the smaller hospitals, 50% never reused, 38% said they reused regularly, and 12% said they did so only occasionally or during emergencies. Interestingly, only 38% of hospitals that regularly reused had written procedures for reuse, and only 32% indicated a mechanism for determining the number of times a device was reused. Cost-analysis studies to demonstrate the economic justification for reuse had been undertaken by only 29% of regular reusers (12). The Canadian survey, surprisingly, does not even mention hemodialyzers and ranks the frequency of reuse reporting among the 377 hospitals that regularly reuse SUDs as follows: Bain circuits, 67% to 70%; nebulizers-humidifiers, 61% to 71%; endotracheal tubes, 13% to 19%; other breathing circuits, 47% to 58%; transducer domes, 7% to 8%; cardiac catheters, 7% to 20%; and arterial catheter needles, 0% to 8%. Current Reuse Prevalence The data cited previously reflect the situation in the 1980s. By the year 2000, a number of reliable surveys suggested that only 20% to 30% of American hospitals were reusing SUDs and that one third of those hospitals relied on a third-party reprocessing company to do the job. The Government Accounting Office (GAO) report (13) that summarized these surveys also provided the most comprehensive and certainly the most objective evaluation of the SUD reuse issue known to me. The most recent update on reuse prevalence is derived from an FDA telephone survey of all hospitals in the country (except military and Veterans Administration institutions) carried out between December 2001 and February 2002 (14) The response rate was nearly 80% and verified that 24% reuse SUDs. The most common devices reused were sequential compression device (SCD) sleeves (15.8%), followed by “drill bits, saws, blades, or burrs” (7.3%), “biopsy forceps, snares” (6.2%), “endoscopic/laparoscopic scissors, graspers, dissectors, or clamps” (6.1%), and electrophysiology (EP) catheters (3.9%). Nearly half of all hospitals with more than 250 beds reuse SUDs, compared with only 12.3% of hospitals with less than 50 beds. This probably reflected the new FDA regulations that were looming on the hospitals' horizons; most reusers (84%) used the services of third-party reprocessors. The majority of the remaining in-house reprocessors (60% of the 15.4%) were small hospitals with less than 100 beds. MEDICAL RISKS ASSOCIATED WITH REUSE OF SINGLE-USE DEVICES The recycling of SUDs poses two kinds of problems: medical risks that may result in physical and physiologic harm and nonmedical problems that derive from the economics, possible liability, and ethics of the practice. Among the potential medical risks, Phillips (15) included the following: Infection risk: the medical device in question may become contaminated during the first use or during the reprocessing procedure. If for any reason the hospital's CSD is incapable of properly resterilizing the device (see Chapter 86), it becomes a potential infection hazard to any patient on whom it will be reused. Pyrogens: medical devices may become contaminated with gram-negative bacteria during patient use or subsequent rinsing in contaminated water. Sterilization destroys the viable microorganisms, but the residual lipopolysaccharide or endotoxins may remain. These chemicals can cause febrile reactions in patients even if the reused device is sterile (see Chapters 62 and 64). Toxic residues: the recycling process involves decontaminating, cleaning, and sterilizing with a variety of germicides, detergents, and toxic gases. If these chemical residuals are not completely removed, they can irritate and harm the tissues of the patient on whom they are reused. Bioincompatibility: devices that have been implanted in a patient or that have had significant contact with the patient's body tissues and fluids may become coated with some of his or her unique cells and biochemicals. If the device is reused on another patient without scrupulous cleaning and removal of those biochemicals, they might generate foreign-tissue reactions and lead to immunologic rejection of the device. Functional reliability: as devices are used over and over again, it might be expected that they will gradually lose the original functional reliability that they had when new. The electronic, mechanical, optical, and physical properties of any device usually deteriorate with age and repeated use. How can a hospital determine the number of times a device can be safely reused without experimenting and placing patients at riskn? Physical integrity and sterile barriers. What is the effect of repeated use, cleaning, and sterilizing on such properties as tensile strength of a device, burst pressure, leak pressure, surface finish, dimensional tolerances, and membrane integrity? Do the materials used to construct medical devices suffer from fatigue? How many times can they be reused safely before failure? All of the risks, catalogued previously, are consistent with theory and have happened in practice. However, they apply to all devices, reusables and previously used SUDs, which are really the subjects of concern in this chapter. In theory, used SUDs pose even greater risks because of several extenuating circumstances that have already been alluded to previously, such as the questionable ability of the average hospital CSS to conduct technically demanding QA tests of safety and function, the common use of nondurable raw materials for SUD fabrication, the inability of CSS cleaning and sterilizing practices to process a SUD that has not been designed or constructed to be compatible with the CSS system, and the unwillingness of the SUD manufacturers to provide instructions for reprocessing a given device. No matter how compelling the theory, what is the evidence P.1540 that SUD reuse poses a real risk for real patients? There are three potential sources for this kind of information: hospital and medical record surveys, anecdotal reports, and systematic epidemiologic studies. DOCUMENTING REUSE PROBLEMS Two studies from the early 1980s (16, 17) are characteristic of the time and the type of information then available. In one 326-bed hospital there were 623 instrument failures in 22 months. Seventy percent of these were associated with SUDs. No mention was made whether these were new or reused devices. In a 452-bed university-affiliated hospital there were 224 incidents of equipment failure in 36 months. The majority involved SUDs being used for the first time. The stated policy of this hospital was not to reuse. Thirty-six of the 224 incidents involved invasive procedures. Perhaps the most comprehensive and certainly the most recent survey was reported by the FDA (18), based on their medical device report (MDR) system. The CDRH is supposed to receive “event reports” about inadvertent outcomes (e.g., injuries) in the field that can be attributed to medical devices, but they concede that the MDR system does not enable accurate assessment of failure rates. Their most recent evaluation is based on the 3 years from 1996 to 1999. Of 300,000 reports submitted, 219 involved hemodialyzers (which are strictly speaking, not really SUDs), and 245 other adverse events could possibly be attributed to reuse of 70 different SUDs. In truth, the general impression shared about the risks of reusing SUDs is derived not from MDRs but from historical anecdotes reports of isolated events that occurred 20 or 30 years ago. These events actually happened and were sufficiently newsworthy to receive wide publicity or sufficiently egregious to result in generous damage awards after litigation. However, there is rarely sufficient information from anecdotal reports to compare relative risks (RR) of infections, endotoxic reactions, or equipment failure associated with reused SUDs vis-à -vis unused SUDs vis-à -vis classical reusable devices. Some of these reports are cited as evidence that the concerns described previously are not just theoretical and that reprocessing and reuse of disposable devices do (or did) involve some health risks. Perhaps the most notorious incident involving a reused product was the Mosely case—a legal action in which a doctor and a hospital were held liable for $970,000 in damages after a cardiac catheter broke and became lodged in a patient's thigh. This was actually a reusable device labeled by the manufacturer for a maximum of three uses. However, it had been reused at least 19 times and had been recalled by the manufacturer 9 years before the incident. When the manufacturer's representative contacted the hospital after the recall, he was informed that none of the items remained in use. However, a search revealed that 53 of the dated catheters were in stock; they were used regularly although some had not even been sterilized (19). A more recent and relevant case of structural weakening because of SUD reuse was described by Fishman (20). An aluminum stylet, the manufacturer of which had cautioned against reuse, broke off in the esophagus of a 72-year-old patient during intubation and ultimately perforated her duodenum. Apparently, the cleaning and sterilizing procedure caused the stylet to lose its malleability, and the metallic structure was sufficiently compromised to permit breakage. Butler and Worthley (21) reported several adverse outcomes associated with the reuse of flow-directed balloon-tipped catheters and demonstrated that devices resterilized with EO were less rigid and had an increased incidence of balloon rupture compared with new devices. The greatest incidence of rupture occurred during the third use, and they recommended that the instrument be recleaned and resterilized for only one extra use; beyond this limit, both function and structure were significantly compromised. Repeated EO sterilization can also weaken the structural integrity of single-use (polyvinylchloride) esophageal stethoscopes. Bryson et al. (22) described how one of these devices, which had been cleaned and resterilized “for economy,” fragmented during a routine thoracotomy and had to be removed in several pieces in the recovery room. Resterilization with EO caused structural damage to a thin (0.003 in.) polycarbonate membrane in the single-use dome of a blood pressure transducer. As the number of sterilizations increased, the probability of a defect also increased. The minute cracks that resulted, cracks that could not be detected by routine CSD monitoring, seriously compromised the sterile integrity of the device. In a 1976 outbreak, 25 patients developed primary bacteremia with Serratia marcescens, and four died during the 4.5-month period when single-use domes were being reused on blood pressure transducers (23). In fairness, it should be reported that contaminated reusable pressure transducers were also implicated in a number of other nosocomial infections episodes during the 1970s (24, 25). The outbreaks involved S. marcescens, Pseudomonas species, Enterobacter species, Candida species, and hepatitis B virus and were responsible for several fatalities. In these cases, however, improper cleaning and sterilization of the devices were blamed not compromise of sterile membrane barriers. When appropriate sterilization and disinfection practices were introduced, the outbreaks were brought under control. In contrast to the cardiac catheter experiences described previously, the infection risk associated with the reuse of single-use plastic insulin syringes seems negligible. Reports from California (26), Virginia (27), Ireland (28), Scotland (29), and Australia (30) all agree that the practice combines both cost benefits and safety. Nearly all of this reuse involves a given patient reusing the same syringe, and the insulin for injection is formulated with antibacterial agents that suppress growth of contaminants. However, these findings cannot be extrapolated to the hospital, where cross-infection via inadequately sterilized devices is much more probable. Other reports of infections associated with the reuse of SUDs incriminated hemodialyzers and blood lancets. The lancet incident occurred in a private physician's office in which 18 cases of hepatitis B could be traced to a nurse's reuse of single-use blood lancets for hemoglobin testing (31). One wonders how much money that nurse actually saved. Reprocessed hemodialyzers identified as SUDs have not only been incriminated as sources of infection but also have been reported as the sources of pyrogenic reactions (32). The infection P.1541 problem is being solved by more comprehensive high-level disinfection protocols, but the pyrogen control is much more complex. This finding has serious implications because of the prevalence of reuse of these devices and the general acceptance that, if the hemodialyzer's reuse is restricted to the same patient, the procedure is actually beneficial. The dialyzer situation is thoroughly reviewed in Chapter 64. Endotoxic reactions were also observed following reuse of cardiac catheters (33, 34) (see Chapter 62). Again the problem was not so much intrinsic to reuse as it was to inadequacy of the reprocessing system. Jacobson et al. (35) conducted a carefully controlled trial of patients studied with both single-use and reused catheters. They concluded that if the catheters were carefully cleaned and reused, there was no statistical difference in infection rates or endotoxic reactions between new and reused devices. Most of the anecdotal events reported previously occurred 2 decades ago, when recycling protocols for used SUDs were still in early stages of development. It should not come as a surprise that infections and pyrogenic reactions occurred. Over the years, however, hospitals learned from their mistakes and perfected more suitable recycling processes for various SUDs just as they did previously for durable devices. It may not be fair to assume that the problems described previously are still current. What is the risk situation now? Systematic studies of SUD-reuse problems do exist and some are very well designed and executed. Their most common drawback, usually beyond control of the investigators, is inadequate sample size, lack of suitable controls, and the inability to “blind” the clinician who is doing the procedure and evaluating the outcome. These faults seriously limit the generalization of their findings to other hospitals or devices. Some studies may be flawed by commercial bias. Not surprisingly, those sponsored by SUD suppliers suggest that reuse results in considerable numbers of QA failures. In contrast, hospitals and physicians who practice SUD reuse and who have a financial incentive to do so point to impressive track records with no adverse iatrogenic events. It is quite possible that both are right. Much depends on what one is looking for and how hard (and long) one looks. Several recent reports are cited as examples. Jacob and Bentolila (36) described an extensive and comprehensive study of contaminated angioplastic catheters conducted at two hospitals in Quebec. They challenged the hospitals' sterilizing systems (EO) with a variety of catheters, various bioloads inside and outside the lumens, and heavy loads of liquid and dried blood occluding the microbial contamination. They concluded that the risk of infection is not significantly higher with reused catheters than with new ones. They also verified that their presterilizing cleaning technique with pyrogen-free water and judicious choice of cleaning chemicals solved the pyrogen and toxic residual problem. Mechanical tests on several types of SUDs revealed that they did not become more fragile after multiple use but emphasized that this aspect of safety must be established de novo for every new type of catheter that is purchased. Kazorek and his colleagues (37, 38, 39) conducted several prospective studies on the reuse of sphincterotomes and biopsy forceps sold as SUDs. They ascertained the sterilizability of the devices after artificial challenges with contaminants and after use in the clinical setting and the number of times that the devices could be reused before a critical malfunction would occur. Most important, they carried out a cost analysis of comparing reusable, disposable, and reprocessed disposable devices. Although some of their clinical trials enrolled too few patients to reach broad generalized conclusions, there is no doubt that these workers could successfully practice modern gastroenterology with reused SUDs and save significant sums of money for their hospital. A randomized, double-blind, controlled clinical trial was conducted in Kuwait by Zubaid et al. (40) to compare the safety (clinical success) and efficacy (angiographic success) of reused versus new coronary angioplasty balloon catheters. There were no significant differences in incidence of balloon failure in the two groups, the angiographic success rate was similar, and the number of catheters used per lesion, amount of contrast, and procedural and fluoroscopy time were similar. After 30 days, the incidence of major adverse cardiac events was similar and the incidence of fever no different. In contrast to the studies that demonstrated feasibility of reuse, Heeg et al. (41) in Germany concluded that none of the SUDs they studied (biopsy forceps and papillotomes) were effectively cleaned, disinfected, or sterilized. Moreover, there was some material damage to the structure of the fragile devices. The scanning electron micrographs of the residual contamination on the SUDs after reprocessing dramatically demonstrated the inadequacy of the cleaning process. In all fairness, however, it should be emphasized that these investigators were also unable to sterilize reusable biopsy forceps, papillotomes, and a stone retrieval basket that had been included as controls. Is it possible that the bottom line of this study—sponsored by a leading SUD manufacturer—is the self-serving conclusion not to reprocess anything—neither SUDs nor reusables? A significant contribution to the debate was made by Chaufer et al. (42) in Australia who evaluated the transmission of live viruses via reusable angioscopes. Thirteen of these devices became contaminated with duck hepatitis B virus (DHBV)-containing blood after examining an infected duck. After a variety of cleaning, disinfection (glutaraldehyde), and sterilizing (EO) treatments (and combinations of these), the angioscopes were reused to examine healthy ducks. All 38 control (no treatment) birds became infected. No disease was transmitted by devices properly cleaned and sterilized. However, if the instruments were inadequately cleaned, DBHV survived despite disinfection or sterilization. Perhaps the a fortieri argument may be made that if it is so difficult to render reusable devices safe and effective (devices designed for recycling and backed by decades of empirical success), the probability of succeeding with recycled SUDs is considerably diminished. This point is reinforced by an in vitro study recently published by Luijt et al. (43). They deliberately contaminated disposable catheters with an RNA virus (echovirus-11) and a DNA virus (adenovirus-2), reprocessed them by cleaning and sterilizing with glutaraldehyde, and simulated their reuse. After performing polymerase chain reaction (PCR) and cell culture assays they concluded that, even after vigorous cleaning and sterilization, virus was still present in the device and that catheters labeled for single-use only should not be reprocessed. Plante et al. (44) stirred the crucible of controversy somewhat P.1542 with a 1994 study that challenged the official premise of the Ministry of Health of their own province (36), namely that reuse of coronary catheters is safe, effective, and economically justified. These investigators conducted a prospective observational study of 693 patients undergoing coronary angioplasty in two hospitals, one of which reused single-use catheters and the other one did not. Reuse involved more devices per procedure (2.4 vs. 1.5), had a higher incidence of initial balloon failure (10.2 vs. 3.3), prolonged procedure time (81 vs. 68 minutes), and required an increased volume of contrast medium (201 vs. 165 ml). Reuse was also associated with a higher rate of adverse clinical events (7.8% vs. 3.8%). There was no significant difference in the very low incidence of fever in either group (3/320 vs. 1/373) and in no case did the fever appear to be related to the catheterization procedure. To be fair, they reported that the hospital that reused the SUDs saved $110,000 CDN during the 10-month course of the study. It is quite common when faced with research results that contradict one's own position—in this case, the argument that SUD reuse is safe, effective, and economical—to reanalyze the opponent's contradictory data, preferably with a sophisticated statistical technique that might discover serious flaws. Two years after it appeared, a reanalysis of Plante's paper was published by Mak et al. (45) in an equally distinguished journal. The latter made several justifiable criticisms and his new calculations dampened the difference in outcomes between the patients treated with only new SUDs and those in whom SUDs were reused. However, he could not counter the observation that reused catheters failed more frequently than new ones, required more frequent replacement, and significantly lengthened duration of the procedure. The bottom line regarding nosocomial infection risks associated with reusing SUDs is that they exist and may not be dismissed as trivial. However, there is no compelling evidence, certainly not from recent studies and not from consideration of the prevalence of the practice, that these risks are significantly higher than those experienced with new SUDs or traditional reusables. The other problems cited by Phillips (15), namely pyrogens, toxic residues, bioincompatiblity, functional reliability, and physical integrity really require further and more systematic study before reaching rational conclusions about risks of SUD reuse. The overwhelming impression conveyed by the most reliable sources is that the harder one looks the more one finds and much depends on who is looking. A scanning electron microscope reveals residuals that could be missed by ordinary light microscopes. Tests that measure compression strength, leak rates, resonant frequency, and other equally arcane criteria that are used by QA engineers to judge function and integrity might reject devices as unsuitable even if the physician claims that “they work fine.” The duration of an angioplastic procedure probably depends as much (or more) on the patient and the physician as it does on the number of times that the catheter has been recycled. In the past, hospitals have focused much of their attention on the cleaning, sterilizing, and infection problems of used SUDs and largely ignored structural and functional QA. It may very well be the case that the latter should play a greater role in deciding whether to continue reuse practice or, at the very least, in making device-by-device decisions. The only answers currently available are track records of empirical success. Moreover, without a fuller and more comprehensive record of all device-related events, one cannot tell whether the damage resulted from reuse per se (as would be suggested by theory), whether the process used to recycle them was inadequate and correctable, or whether the process was simply not carried out properly. The track record suggests that many items labeled as SUDs can actually be recycled several times safely. Nonmedical Problems Associated with Reuse of Disposables Even if the technical and medical issues are in order, certain economic, legal, and moral ramifications of SUD reuse suggest strongly that the practice should be severely curtailed or at least more deeply reexamined. This is not be the appropriate medium for a thorough analysis of these issues, but a brief review of some of the questions that have been raised should illustrate the point. Power and Politics The debate about reusing SUDs goes beyond the ivory towers of academia and the drab cubicles of bureaucracy. It reflects a serious struggle between several powerful forces—the hospital world, healthcare professionals, the device supply industry, government regulators, and others—with some very significant stakes in contention: turf control, money, the health of the public, hospital traditions, and employment of the working poor. The numbers and diversity of groups whose members stand to lose or gain—sometimes their very livelihood—depending on decisions reached about reusing or discarding SUDs is impressive [e.g., see the Web site maintained by the Association for Advancement of Medical Instrumentation (AAMI)] (46). Each side tries to present those data and arguments that paint it in the best possible light and tries to obfuscate the opposition. Under these circumstances, scientific truth and objectivity is sometimes difficult to ascertain Economics The original justification for reusing SUDs—saving money—has been challenged from the very beginning (47, 48, 49). These authorities point out that most hospitals involved in SUD reuse do not carry out proper cost-accounting studies that would validate such savings and that those few who do studies overlook a number of direct and indirect costs involved. For example, they do not factor into the equation the extra time required to do a procedure with reprocessed SUDs that may be functional but not quite as flexible or manageable as new unused devices (44) or the number of recycled devices that would be rejected by the practitioner during the procedure. They ask about the point in the reuse sequence at which savings move from “negligible” to “significant”: Do we reuse a SUD to save $100 or $10 but do not think it worthwhile to save $5? How many times? Until it fails or when it reaches the 50% point in its “life expectancy” cycle? Who decides? Critics of reuse claim that hospitals do not even factor into P.1543 their economic incentive calculations the potential legal costs that will be faced if a patient dies or is injured by a SUD used contrary to manufacturers' warnings. Others emphasize the costs of establishing a proper QA program to minimize such events; they point out that if a hospital had to spend money on QA, the savings realized from reuse of disposables would soon evaporate. This is apparently what will happen when the new FDA policy transfers SUD reprocessing from the hospital to a commercial, outside facility. Some of the most biting criticism of SUD reuse deals with the question, “Who really benefits economically?” Is the patient examined with a cardiac catheter, previously used 20 times, charged less than the patient who was number 10 in line? Is it fair to charge them the same? And if we do, is it the average cost of a reused SUD, or the prorated cost after each reuse, or the original price of the brand new one? Does the hospital pocket the savings? Or the insurance company? Or Medicare? Do we even tell the insurance carrier that we are using reprocessed SUDs and charging as if they were new? Legal Considerations Liability questions associated with SUD reuse are as intriguing and frustrating as those of economics. The point is that there is no specific law against reuse that would expose the reuser to criminal charges. However, there are more than a million attorneys in the United States, most of whom earn their livelihood from litigation and a large number of these from litigation in the fields of medical malpractice, product liability, and personal injury. There is remarkably little statute law on the books dealing with the reuse issue, and there is a dearth of case law on the subject. Until the FDA's initiative in 2000 to treat reprocessing of SUDs as a manufacturing activity that came under its jurisdiction (see later) there was a confusing hodgepodge of directives, guidelines, regulations, advisories, licensing criteria, and codes emanating from governmental agencies, professional associations, and conference proceedings that related to safety and effectiveness of reused devices. The jungle is always ecologically ripe for an explosion of litigation. Good reviews of the liability issues relative to SUD reuse can be found in the 1983 AAMI report (50) and the 1984 Georgetown conference proceedings (51); a brief but more recent summary was published in the 1992 Emergency Care Research Institute (ECRI) newsletter (19) already cited. It should also be noted that he new FDA initiative does not ban reuse in the hospital. The hospital may still be caught in the “litigation net” along with the third-party reprocessor if some undesirable event occurs and plaintiff's attorney demonstrates that reuse, in that particular case, of a device labeled for single-use only was a negligent act. Ethical Concerns The ethical arguments against the reuse of SUDs are even more compelling than the economic uncertainties and the fears of litigation presented previously. If by reusing SUDs, the hospital is exposing itself to unnecessary legal liability and associated costs of litigation, the practice has little, if any, moral justification and requires very little further analysis. Win or lose, the litigation will certainly raise the costs of medical care, and the practice has a negligible, even questionable, benefit to the patient or the hospital. However, the moral issues go much deeper. How do we reconcile patient autonomy and justice in a situation in which one patient gets a brand new device and the next gets a device for which the manufacturer denies responsibility? How do we frame the informed consent questions? Who will be first and who last? How did the hospital originally determine the limits of reuse before it started the practice? Or was this a kind of empirical clinical trial on human beings without their informed consent and without permission from the institutional review board? The questions about charging for SUDs have been mentioned previously; they might sound flippant and insignificant in view of the huge costs of medical care, but there are some basic issues of honesty and potential fraud involved. The fundamental ethical question in SUD reuse, as in most other biomedical issues, must deal with the beneficence of any practice versus all of the other values, such as justice, autonomy, and risk of harm (52). Here the answer seems clear. Except for the case of previously used dialyzers (with which some benefits to the patient are clinically discernible along with some risks), a patient treated or diagnosed with a reused SUD is no better off and is theoretically at higher risk than a patient exposed to the prepackaged, presterilized, and previously unused device. If there are other benefits, such as monetary savings for the patient, this might become a question of informed consent. If the patient will be deprived of treatment or care because the only device available has been previously used and reprocessed, this is also a matter of informed consent. However, the bottom line is benefit to the patient, and, until the advocates of reuse can demonstrate this with data, the practice should be avoided. THE NEW FDA APPROACH TO THE ISSUE OF SUD REUSE The Medical Device Amendments of 1976 require the FDA to see that devices that enter the market are safe and effective and to ensure that they remain that way. The position of the FDA then, a position which has not really changed today, is that their regulatory authority relates to manufacture of medical devices rather than to their use (10). Thus, when some medical practitioners started to recycle their more expensive and sophisticated SUDs in the 1970s to save money, the FDA did not exert any regulatory efforts to outlaw the practice, although they were aware of its rapidly rising prevalence and the early reports of associated casualties (23). They issued guidelines in 1981, addressed to the institutions and practitioners who “reprocess and reuse disposable medical devices,” instructing them to be able to demonstrate “(1) that the device can be adequately cleaned and sterilized, (2) that the physical characteristics or quality of the device will not be adversely affected, and (3) that the device remains safe and effective. Also, the user must bear full responsibility for reuse.” Sixteen years after these positions were presented at the Georgetown Conference (10) the FDA completely reversed its approach to SUD reuse. The current director of CDRH read a statement (18) before P.1544 a Senate committee in June, 2000, in which he stated that the FDA “has re-examined its policy on this issue” and reached a “decision to treat all reprocessors of SUDs, whether third-party firms or hospitals, in a similar manner,” namely as manufacturers of medical devices and subject to the same licensing, inspection, regulation, and noncompliance penalties as commercial OEMs. In other words, the FDA, which is constrained from simply banning SUD reuse because that is essentially a medical practice option, is redefining some aspects of the SUD-reprocessing operation to accomplish the same end. A used SUD would now be considered “raw material.” The cleaning, testing, packaging, and sterilizing steps that are daily done to recycle reusable devices in every CSS in the country, would be considered a manufacturing process when recycling SUDs. The hospital in which this was done would now be recognized as an OEM, which would ironically be required to label the reprocessed used devices for single-use only! Because of this, the hospital would have to adhere to all of the premarketing requirements incumbent on all OEMs of medical devices and go through the technical and bureaucratic steps of validating their procedures and QA standards through the CDRH. The details, deadlines, fines for noncompliance, and updates of FDA new approach can be accessed on the Internet (53). In previous editions, the chapter on SUD reuse ended with a plea to hospitals to “|.|.|. do what they do best—provide medical and surgical and rehabilitative care to patients—and let industry do what it does best—supply safe and effective devices to the hospital and practitioner.” The new FDA policy seems to reinforce this advice. Certainly the decreased prevalence of SUD recycling, cited earlier, demonstrates that the practice in American hospitals has dropped significantly in the last few years. However, if the new directives just remove the in-house phase of reprocessing, transfer it to a third-party, and continue to allow devices to be used over and over again contrary to the advice of the original manufacturer, the legal and ethical issues have not been resolved. It should be emphasized once again that, if a medical device is not designed for reuse, it should not be reused or it should not be reused until the patient is aware of what is taking place and consents to it. Actually, those with the most experience in the field believe that this is not only the end of SUD reprocessing in the American hospital but also that it is the end of SUD reuse, period! In a brilliant essay Favero (54) suggested that hospitals do not want to become nor will they be able to afford the cost of becoming OEMs. Furthermore, the third-party reprocessors have also been redefined as OEMs and will have to dance the same dance as the real OEM with respect to manufacturing practices, premarket approval, inspections, QA validations, ad infinitum. In turn, the extra costs that OEM status will entail and which they will have to pass on to their hospital customers will reduce any financial advantage that used SUDs used to have over brand-new ones. Perhaps this is what FDA wanted in the first place—to terminate SUD reuse without banning it. If so, it is an ingenious ploy. Why they changed their mind after nearly 3 decades of basic inaction except for guidelines and platitudes is another subject for historians to elucidate, particularly because they did it just when the hospitals were getting so proficient at recycling. One of the more noteworthy quotations from the Senate hearing stated “Despite a lack of clear data that directly link injuries to reuse, FDA has concluded that the practice of reprocessing SUDs merits increased regulatory oversight” (18). Will the next FDA policy reexamination lead it to extend its oversight to the world of reusable devices? Will Dr. Favero's next requiem be offered for the venerable hospital institution known as the CSS? CONCLUSIONS Analysis of the historical, epidemiologic, and regulatory literature pertaining to the reuse in hospitals of medical devices labeled for single-use only or SUDs leads to the following conclusions: Compared with previously unused devices, reused SUDs should in theory pose increased risks of infection; a higher incidence of febrile reactions from pyrogenic residuals; irritation from toxic residues deposited by cleaning and sterilizing chemicals; immunologic reactions to foreign tissue residues on previously implanted devices; a higher incidence of electronic, mechanical, optical, and physical malfunctions; and diminished physical integrity of the device and integral sterile barriers. In clinical practice, however, empirical evidence from institutions that have been reusing SUDs for decades does not support the premise that the practice demonstrably endangers their patients' life and health. Systematic and controlled prospective studies in this field provide contradictory results. Many of the studies are flawed by inadequate sample numbers to provide the statistical power that would demonstrate safety. Investigator bias and commercial bias permeate the literature. The field is in need of some good systematic studies using large numbers of experimental animals. The economic, legal, and ethical aspects of SUD reuse are not the same as those of reprocessing. Even a hospital that delegates the latter to a third-party processor is obligated to obtain informed consent from patients before using them, to make sure that the allocation of new and reused devices is fair, and to return the savings—if any—to the patient. The reuse debate may quickly become (or already has become) moot because of the recent FDA initiative to classify both hospitals and third-party reprocessors of SUDs as device manufacturers who must conform to all of the restrictions and testing standards previously demanded only from commercial manufacturers. This initiative not only removes the economic incentive for reuse but also actually adds a regulatory disincentive. In effect, both SUD reprocessing and reuse will fade from the scene and might disappear. REFERENCES 1. Semmelweis IF. The etiology, concept, and prophylaxis of childbed fever—1860. Madison: University of Wisconsin Press, 1983. Carter KC, translator and editor. 2. Richardson RG. Surgery: old and new frontiers. New York: Scribner, 1968:75–81. P.1545 3. Perkins JJ. Principles and methods of Sterilization in health sciences, 2nd ed. Springfield, IL: Charles Thomas Publishers, 1969. 4. Kilmer FB. Modern surgical dressings. Am J Pharm 1897:69:24–39. 5. Bruch CW. Inhospital versus industrial sterility assurance: is there a double standard? Inhospital sterility assurance-current perspectives. Technology Assessment Report 4-82. Arlington, VA: AAMI, 1982:19–22. 6. Brown RM, ed. Use and disposal of single use items in health care facilities. Ann Arbor, MI: National Sanitation Foundation, 1968. 7. Mayhall CG. Types of disposable medical devices reused in hospitals. Infect Control 1986;7:491–494. 8. Sones M. Position of the Society for Cardiac Angiography. Reuse of disposables. Technology Assessment Report 6-83. Arlington, VA: AAMI, 1983:92. 9. Institute for Health Policy Analysis. Reuse of disposable medical devices in the 1980s. Washington, DC: Georgetown University Medical Center, 1984. 10. Villforth JC. Position of the US Food and Drug Administration. In: Reuse of disposable medical devices in the 1980s. Washington, DC: Georgetown University Medical Center, 1984:91–94. 11. Favero M. Position of the Centers for Disease Control. In: Reuse of disposable medical devices in the 1980s. Washington, DC: Georgetown University Medical Center, 1984:98–101. 12. Campbell BA, Wells GA, Palmer WN, et al. Reuse of disposable medical devices in Canadian hospitals. Am J Infect Control 1987;15:196–200. 13. General Accounting Office (GAO). Single-use medical devices: little available evidence of harm from reuse but oversight warranted. Letter Report, 06/20/2000, GAO/HEHS-00-123. Available at http://www.aami.org/reuse/. 14. Food and Drug Administration. Survey on the reuse and reprocessing of single-use devices (SUDs) in US hospitals—executive summary. Updated 10/16/02. Available at http://www.fda.gov/cdrh/Reuse/survey-execsum.html. 15. Phillips GB. Reuse of products labeled for single use only. Inhospital sterility assurance-current perspectives. Technology Assessment Report 4-82. Arlington, VA: AAMI, 1982:52–54. 16. Beck WC, Geffert JP, Comella LH. Lessons learned from the Hospital Experience Reporting System. Med Instrum 1983;17:343–346. 17. Bancroft M, Bushnell LS. Hospital experience reporting system. Final report, Food and Drug Administration Contract 223-80-5090, 26 Mar 1984. Silver Spring, MD: Center for Devices and Radiological Health. 18. Feigal DW. Statement before the Senate Committee on Health, Education, Labor and Pensions June 27, 2000. Available at http://www.fda.gov/ola/2000/suds2.html. 19. ECRI. Reusing disposable products. Operating room risk management. Plymouth Meeting, PA: ECRI, October, 1992. 20. Fishman RL. Reuse of a disposable stylet with life threatening complications. Anesth Analg 1991;72:266–267. 21. Butler L, Worthley LIG. Reuse of flow-directed balloon-tipped catheters. BMJ 1982;284:207. 22. Bryson TK, Saidman LJ, Nelson W. A potential hazard connected with the resterilization and reuse of disposable equipment. Anesthesiology 1979;50:370. 23. Sterilization and disinfection of hospital supplies. MMWR Morb Mortal Wkly Rep 1977;26:266. 24. Weinstein RA, Stamm WE, Kramer L, et al. Pressure monitoring devices-overlooked source of nosocomial infections. JAMA 1976;236:936–938. 25. Donowitz LG, Marsik FJ, Hoyt JW, et al. Serratia marcescens bacteremia from contaminated pressure transducers. JAMA 1979;242:1749–1751. 26. Crouch M, Jones A, Kleinbeck E, et al. Reuse of disposable syringe-needle units in the diabetic patient. Diabetes Care 1979;2:418–420. 27. Hodge RH, Krongaard L, Sande MA, et al. Multiple use of disposable insulin syringe-needle units. JAMA 1980;244:266–267. 28. Collins BJ, Richardson SG, Spence BK, et al. Safety of reusing disposable plastic insulin syringes. Lancet 1983;1:559–560. 29. Strathclyde Diabetic Group. Disposable or non-disposable syringes and needles for diabetics? BMJ 1983;286:369–370. 30. Stepanas TV, Turley H, Tuohy E. Reuse of disposable insulin syringes. Med J Aust 1982;1:311–313. 31. Phillips GB. The reuse of single use medical devices: issues and impacts. Washington, DC: Health Industry Manufacturers Association, 1984. 32. Gordon SM, Tipple M, Bland LA, et al. Pyrogen reactions associated with the reuse of disposable hollow-fibre hemodialyzers. JAMA 1988;260:2077–2081. 33. Endotoxic reactions associated with the reuse of cardiac catheters—Massachusetts. MMWR Morb Mortal Wkly Rep 1979;28:25–27. 34. Kundsin RB, Walter CW. Detection of endotoxin on sterile catheters used for cardiac catheterization. J Clin Microbiol 1980;1:209–212. 35. Jacobson JA, Schwartz CE, Marshall HW, et al. Fever, chills, and hypotension following cardiac catheterization with single- and multiple-use disposable catheters. Cathet Cardiovasc Diagn 1982;9:39–46. 36. Jacob R, Bentolila P. The reuse of single-use catheters. Report submitted to the Ministre de la Sante et des Services sociaux du Quebec by the Conseil d'evaluation des technologies de la sante. Conseil d'evaluation: Montreal, Canada 1993. 37. Kozarek RA, Raltz SL, Merriam LD, et al. Disposable versus reusable biopsy forceps: a prospective evaluation of costs. Gastrointest Endosc 1996;43:10–13. 38. Kozarek RA, Raltz SL, Ball TJ, et al. Reuse of disposable sphincterotomes for diagnostic and therapeutic ERCP: a one-year prospective study. Gastrointest Endosc 1999;49:39–42. 39. Lee RM, Vido F, Kozarek RA, et al. In vitro and in vivo evaluation of a reusable double-channel sphincterotome. Gastrointest Endosc 1999;49:477–482. 40. Zubaid M, Thomas CS, Salman H, et al. A randomized study of the safety and efficacy of reused angioplasty balloon catheters. Indian Heart J 2001;53:167–171. 41. Heeg P, Roth K, Reichl R, et al. Decontaminated single-use devices: an oxymoron that may be placing patients at risk for cross contamination. Infect Control Hosp Epidemiol 2001;22:542–549. 42. Chaufour X, Deva AK, Vickery K, et al. Evaluation of disinfection and sterilization of reusable angioscopes with the duck hepatitis B model. J Vasc Surg 1999;30:277–282. 43. Luijt DS, Schirm J, Savelkoul PH, et al. Risk of infection by reprocessed and resterilized virus-contaminated catheters; an in vitro study. Eur Heart J 2001;22:378–384. 44. Plante S, Strauss BH, Goulet G, et al. Reuse of balloon catheters for coronary angioplasty: a potential cost-saving strategy? J Am Coll Cardiol 1994;24:1475–481. 45. Mak KH et al. Absence of increased in-hospital complications with reused balloon catheters Am J Cardiol 1996;78:717–719. 46. AAMI resources on reuse of single-use devices. Updated 01-31-02. Available at http://www.aami.org/reuse. 47. Romeo AA. The economics of reuse. In: Reuse of disposable medical devices in the 1980s. Washington, DC: Georgetown University Medical Center, 1984:43–49. 48. Duffie ER. Concerns of the medical device industry. In: Reuse of disposable medical devices in the 1980s. Washington, DC: Georgetown University Medical Center, 1984:107–112. 49. Jarvis AE. Reuse and product development, production, quality assurance, and cost. Reuse of disposables. Technology Assessment Report 6-83. Arlington, VA: AAMI, 1983:62–64. 50. Salman SL. Reuse and insurance coverage. Reuse of disposables. Technology Assessment Report 6-83. Arlington, VA: AAMI, 1983:41–43. 51. Novak N. Legal concerns surrounding the reuse of disposable medical devices. In: Reuse of disposable medical devices in the 1980s. Washington, DC: Georgetown University Medical Center, 1984:56–72. 52. Beauchamp TL. Moral problems in the reuse of disposable medical devices in the 1980s. Washington, DC: Georgetown University Medical Center, 1984:50–55. 53. Reuse of single-use devices: Key Government documents. Available at http://www.fda.gov/cdrh/reuse/index.html. 54. Favero MS. Requiem for reuse of single-use devices in US hospitals. Infect Control Hosp Epidemiol 2001;22:539–541.
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Although chemicals have been used empirically for centuries to preserve foods, sterilization methods for medical equipment and devices are a relatively recent development. The recognition and acceptance of germs as a causative agent of disease led, in the mid- to late 1800s, to the realization that removal of germs from surgical instruments and other hospital equipment would protect patients from life-threatening infections. Pasteur's laboratory experiments led him to discover the dust on his laboratory instruments and that passing them through a flame before use prevented contamination of his experiments (1). The use of heat as a sterilizing agent was not readily accepted, but as the positive results became known, more emphasis was placed on sterilization processes in the medical field. Sterilization has become a prerequisite for certain procedures and devices, and a whole industry has been developed to provide new, better, and more cost-effective ways of ensuring sterilization of medical equipment and devices. It is important to understand the terminology and technology of sterilization and to recognize the importance of following appropriate procedures to achieve sterilization. In addition, it is important to understand the need for and methodology of validating and documenting sterilization procedures. Failure to implement the appropriate sterilization process leads to contamination of critical instrumentation, infection of patients, and potential loss of life. In many cases, the destruction of common pathogens is sufficient for a particular process. However, it is important to remember that any microorganism in the wrong place at the right time is a potential pathogen. Because the current patient population is at particular risk for infection due to immune incompetence (patients infected with the human immunodeficiency virus, transplant patients, cancer chemotherapy patients, and elderly patients), sterilization verification becomes even more important. In addition to their concern for proper sterilization processes and protection of patients, healthcare administrators must also be concerned with the health and safety of their personnel and the potential for environmental contamination. Sterilization processes designed to destroy microorganisms carry with them the potential to harm the personnel who must perform the processes and the potential to result in environmental damage. Appropriate mechanisms for minimizing personnel exposure and environmental release must be developed and incorporated in the operation of the healthcare facility. DEFINITIONS Disinfection is a process that results in the destruction of infectious agents on inanimate objects but does not necessarily destroy all bacterial spores. The process may be a result of treatment with chemicals or physical agents. Although the term disinfection is often used synonymously with sterilization, it is not the same, and the two processes should be considered separately. Disinfection is the subject of Chapter 85 and is not further considered here. Sterilization, on the other hand, is defined as a process that results in the destruction or elimination of all forms of life, including bacterial spores. The term is most often used in the context of destroying microorganisms. Sterilization is an absolute in that a material, when sterile, cannot be contaminated with any form of viable microorganism. However, the term has been used to denote the filter treatment of fluids that removes bacteria, fungi, and spores but not viruses. Therefore, one must understand the limitations of the sterilization process before accepting the product as truly sterile. The verification of sterility would necessarily depend on the ability of personnel to demonstrate the destruction of all living microorganisms. Such verification would suppose that we have knowledge of all living microorganisms and can demonstrate their existence. Because this is virtually impossible and totally impractical, the efficacy of sterilization processes is most often demonstrated through the use of known highly resistant microorganisms as indicators, and the verification of sterility becomes a matter of probability. The assurance of the completion of the sterilization process is different for differing operations and is measured by the percentage of reduction, or log reduction (D value), in initial counts of biologic indicators that is accomplished by the process. Pasteurization is historically defined as the heating of materials to temperatures of around 60ВC for 30 minutes to destroy pathogens that may be present, although other time/temperature relationships have also been used. The process of pasteurization is also used for the reduction of infectious agents in liquids and has been tried in the processing of various devices, particularly anesthesia equipment and various types of scopes. It should be noted that this is not sterilization and should not be used for devices when there is a critical need for a sterilized product. P.1524 Filtration is another mechanism for treatment of air and fluids to reduce microbial contamination. Although filtration is often referred to as a sterilization process, it is possible for viral particles and bacteria to pass through many filters. Properly chosen and controlled, however, this process can be used to ensure that fluids and air are free from bacterial, mold, and particulate contamination. CRITERIA OF STERILIZATION Several criteria of sterilization as an absolute process should be recognized: Thermal death time: the time required to kill all spores at a specified temperature; D value: the time required to reduce the microbial population by 90% or 1 log; F value: the time in minutes required to kill all the spores in suspension when at a temperature of 121ВC or 250ВF. The D and F values can be used to evaluate various methods of sterilization. PRINCIPLES OF STERILIZATION The kinetics of inactivation and principles of thermal destruction of microorganisms are beyond the scope of this chapter; interested readers are referred to the excellent treatises of Wickamanayake and Sproul (2) and Pflug and Holcomb (3). The efficacy of various sterilization processes depends on a number of factors. Each factor that must be considered in choosing a particular process and determining the efficacy of that process is discussed below. Natural Resistance Sterilization depends on the inactivation of microbial life processes faster than the microorganism can replace or repair the destroyed cell material. Death curves for microorganisms are generally accepted to be logarithmic, and variations from log death curves are considered to be due to variations in the nature of the microorganisms in question (4). Some antimicrobial agents (chemical disinfectants and antibiotics) react with crucial enzymes or interfere with enzyme systems within the cell. Cells that are not killed by the initial insult often are genetically different from those that are killed and have altered enzymes or enzyme systems that allow for survival. These microorganisms then multiply and become the resistant population. Sterilization processes do not lead to resistant populations because, by definition, all microorganisms are killed by the process. However, even in regard to sterilization processes, genetics do play a significant role in protection of microorganisms. For example, bacterial spores are significantly more resistant to various sterilization processes than are vegetative cells. The natural resistance of spores is primarily due to the chemical composition of the spore coat and differs for different genera and species. The requirements for sterilization differ for different microorganisms according to the genetic makeup of the microorganism. Some microorganisms grow well at temperatures normally used for pasteurization and must be treated at higher temperatures. Some microorganisms can rapidly repair radiation damage; thus, the level and duration of radiation treatment must be increased to ensure inactivation. Some microorganisms can find their way through filter materials, and the final use of the filtrate must be considered. This is not to imply that sterilization cannot be accomplished, but only to point out that the process must be carefully determined and scrupulously monitored to ensure the desired result. Microbial Load and Extraneous Organic Materials The final outcome of the sterilization process depends on the numbers of microorganisms initially present in the material to be sterilized, and the values that define the process all depend on the initial number of microorganisms. Therefore, the higher the number of microorganisms in or on the materials to be treated, the longer or more concentrated the treatment must be to achieve sterilization. In addition to the effect of bioburden on the final outcome of the sterilization process, extraneous organic materials also contribute to the efficacy of the process. As with microorganisms, excess organic material increases the duration of, and changes the requirements for, the sterilization process. Organic material serves to protect the microorganisms from the effects of the specific process and may cause process failure. Sterilization processes have been developed to ensure successful sterilization. Because, in a practical sense, sterilization is a statistical phenomenon, we must assume that a given process will result in complete kill of any microorganisms present, and our assumption must be based on the monitoring data obtained from that process. GENERAL REQUIREMENTS FOR STERILIZATION PROCESSES As in disinfection processes, a number of factors, aside from the natural resistance of spores and other microorganisms, affect the efficacy of any sterilization process. These factors include time, temperature, relative humidity (RH), pH, and standardization of loads. Time All sterilization processes require time for completion. The time required primarily depends on the process (e.g., wet heat, dry heat, gas, radiation). In addition, the time depends on the presence or absence of organic material and bioburden. The time required for adequate processing is determined by the use of indicator microorganisms that are known to be particularly resistant to the process being used. The sterilization process is defined in terms of time required to kill all spores present or to reduce the P.1525 number of microorganisms present by 90%. Because microbial death curves tend to be exponential, extrapolations can ensure that appropriate times are used to allow for destruction of the microorganisms that might be present. Temperature Microorganisms generally have an optimal growth temperature above which they do not grow well or they die. Therefore, increasing the temperature of a sterilization process above the optimal growth temperature for the microorganism in question would increase the efficacy of a process. Relative Humidity The role of RH has been studied with regard to both heat sterilization processes and chemical (gas) processes. RH is defined as the ratio of the actual water vapor pressure in a system to the saturated water vapor pressure of the system at the same temperature. This term describes the water conditions in the atmosphere and as such inherently describes the water condition of the microbial cell or spore. Water activity is the relative water availability in a cell or spore and depends on the RH. There is an inverse relationship of cell resistance to water activity. It appears that, in most instances, the more water available to the vegetative cells or spores, the faster the heat inactivation process. Any sterilization process should account for the RH (5). pH As with disinfectant activity, the pH of the suspending medium appears to play a role in the sensitivity of microorganisms and spores to heat inactivation. A number of studies have demonstrated that a lowered pH may result in decreased resistance to heat treatment for bacterial species and spores, but the opposite is true for yeasts (3). It is postulated that pH changes alter the degree of dissociation of materials in solution, resulting in a shift of the oxidation reduction potential, thus affecting the survival of microorganisms. Load Standardization For all contained sterilization processes, it is important that loads be standardized to ensure a uniform process. Loads can vary in a number of ways, including the number of packs, the volume of the packs, the size of the packs, and the contents of the packs. Failure to standardize loads (i.e., instrument packs, linens, routine loads) adds another variable to the process. Theoretically, if a sterilization container/process [e.g., autoclave, ethylene oxide (ETO) unit] is tested and validated with a given load, any change in that load could result in a failure of the process. However, as a practical matter, the parameters of sterilization are chosen to ensure overkill, and failure of the process is most often due to actual equipment failure or to failure of personnel to monitor or to adequately follow the instructions for performing the process. HEAT STERILIZATION PROCESSES Since the beginning of recorded time, heat in one form or another has been used to cleanse and purify. In the medical field, hot air ovens, which require extended process times to be effective, have been used to sterilize materials and equipment that must be kept dry. On the other hand, moist heat (steam sterilization) processes have been found to be a more rapid and effective method of sterilization for those materials with which they are compatible. Steam Sterilization Steam sterilization is the most common of all the sterilization procedures used in the healthcare facility, because steam under pressure has been found to effectively destroy even the most resistant bacterial spores during a brief exposure. Steam sterilization is universally used except where heat and moisture damage may occur to the material being sterilized. Various types of steam sterilization equipment (autoclaves) have been developed and used with success over the years. It has been demonstrated that moisture is a necessary part of the steam sterilization process, because without moisture the process reverts to a dry heat process and requires longer exposure times. The major design features of steam sterilization equipment involve the mechanisms for removal of air from the load, thus ensuring complete mixing of the steam and elimination of cold spots in the autoclave. These mechanisms include gravity displacement, mass flow dilution, pressure pulsing, high vacuum, and pressure pulsing with gravity displacement. All these methods have been developed to help remove air from the system and from the materials to be sterilized to optimize efficiency and efficacy. Each method has its own deficiencies because of the physics and thermodynamics of steam, air, and water mixtures. The pressure pulsing gravity displacement system has been found to be most useful for general use, because it reduces the thermal lag on heating of the load to the desired exposure temperature. Factors that can affect the efficacy of the steam sterilizer include the air tightness of the sterilizer, atmospheric pressure, quality of steam, and characteristics of the load. In autoclaves that use the vacuum process, air from outside the vessel may be brought in through leaks in the system. This may result in a failure of the system because of uneven heating and spot dry conditions. Autoclaves operated at or below atmospheric pressure are inherently subject to air leaks, and continued vigilance with regard to maintenance of equipment is necessary to minimize potential problems. Joslyn (4) has described a new mechanism whereby sterilization is performed using a pulse method in which the steam pulses are performed at pressures above atmospheric pressure. This process should eliminate problems associated with air leaks because it is performed completely under positive pressure conditions. The quality of the steam introduced into the sterilizer is also important in ensuring appropriate operation of the device. The quality of steam is defined by the weight of dry steam in a mixture of dry saturated steam and water in the system. Ideally, 100% saturated steam P.1526 is required for proper operation of steam sterilizing equipment. Most equipment is designed with a steam separator and baffle that removes the water from the steam and directs the pure saturated steam to the chamber at the required velocity. An appropriately designed autoclave operates efficiently regardless of the quality of the steam delivered to the equipment except when the separator or baffle malfunctions. Decreased steam quality (i.e., increased water content) may result in saturation of the materials such as dressings, wrappings, or linens. Excessive moisture then reduces the diffusion of steam throughout the load and, specifically, throughout the moisture laden packs. This may result in trapped air in the pack and increased time requirements for sterilization. In addition, grossly wet materials do not dry easily when the sterilization cycle is completed, and wet packs easily become contaminated. Rutala et al. (6) showed that the type of container in which bags of waste were treated in a gravity displacement steam sterilizer had a significant effect on the sterilization time. These workers found that stainless steel containers allowed for optimal heat transfer and decreased the time required to sterilize the waste. Although steam sterilization is the most common sterilization process used in the healthcare facility and personnel are most familiar with the process, the maintenance and operation of the equipment must still be closely monitored. The process is extremely complex and can be affected by a number of variables. Personnel responsible for steam sterilization in a healthcare facility should be familiar with all requirements for proper operation of the process. An excellent reference on the subject is found in the Association for the Advancement of Medical Instrumentation's recommended practice (7). Failure to understand the steam sterilization process, the equipment operation, or the validation process could lead to sterilization failure and contamination of critical medical supplies. Flash Sterilization The process of flash sterilization is often used for treatment of items that have become contaminated in the operating suite and will be needed again in a short time. As mentioned in the section on steam sterilization, sterilization requires removal of air and replacement of that air with saturated steam. Materials to be flash sterilized may inherently trap air in the system (e.g., porous linen, lumens of instruments), and varying conditions are necessary with these types of materials to ensure appropriate treatment. Flash sterilization for nonporous items is accomplished by heating to 270ВF (132ВC) for 3 minutes, or 10 minutes for porous materials, in a gravity displacement steam sterilizer. The actual sterilization cycle is the time required to heat up, treat, and cool down the sterilizer and therefore can take as long as 5 to 7 minutes for the 3-minute cycle and 12 to 18 minutes for the 10-minute cycle (8). This process undoubtedly results in the destruction of most vegetative cells and viruses provided they are not protected by excess organic matter and the bioburden is low. Experimental evidence in the laboratory also indicates that the times and temperatures are sufficient to inactivate spores of Bacillus stearothermophilus. However, spore testing with commercial self-contained biologic indicators is often misleading (9). In addition, when this process is used, there is rarely time, before the use of the sterilized item, to allow for incubation of biologic indicators. Because of difficulties in verifying the validation process, Garner and Favero (10) have recommended against the use of flash sterilization for implantable items. The cleanliness of the instruments to be sterilized, the condition of the autoclave, failure to document loads, and autoclave parameters all may affect the outcome of the process. It is important to recognize the shortcomings of flash sterilization and to use this process sparingly if protection of patients from wound contamination is to be ensured. Dry Heat Sterilization Dry heat (hot air ovens) has been used for many years as a method for sterilizing glassware, instruments, and other critical supplies that, for various reasons, could not be sterilized by steam sterilization procedures. Although wet heat sterilization is defined as sterilization at an RH of 1% or 100%, the parameters of dry heat treatment are not so easily determined. Dry heat sterilization takes place at an RH of between 0% and greater than 99%. The conditions for effective dry heat sterilization depend on the amount of water in the materials to be sterilized and in the environment of the dry heat sterilizer. At any given temperature, the lower the RH, the longer the time required for sterilization in a dry heat process. An understanding of this phenomenon explains the conflicting requirements established by various regulatory agencies in different countries with regard to the parameters of dry heat sterilization. Generally, in the United States, the requirement for dry heat treatment of containers for pharmaceutical products is 170ВC for 2 hours. The American process includes a significant protection factor if one assumes that the British Pharmacopeia requirement of 150ВC for 1 hour is also efficacious (11). Dry heat sterilization advantages include low corrosiveness and deep penetration. However, the heating process is slow, and long sterilizing times are required. Materials may also be damaged by exposure to high temperatures for long periods. Although a number of testing procedures have been developed to demonstrate the dry heat inactivation of microbial cells and spores, none of these is readily acceptable as a routine mechanism for deciding the exact time and temperature to be used for the process in the hospital. A description of these tests is beyond the scope of this chapter. It should be sufficient to recognize that the process recommended in the U.S. Pharmacopeia includes an appropriate protection factor and therefore should be a safe procedure when necessary. GAS STERILIZATION Since before the time of Hippocrates and the proclamation of the belief that infections were caused by miasmas and bad vapors, humans have sought a means of combating infectious diseases through the use of gaseous agents. The use of incense and frankincense was associated with concepts of purification of the air. Spices were placed in foods in the hope that their strong odors would prevent spoilage. In more recent times, the aerosolization of carbolic acid in operating rooms by Joseph P.1527 Lister, the use of sulfur dioxide and chlorine for terminal disinfection of a sick room, and the introduction of the use of formaldehyde for the same purpose did much to stimulate research on methods and mechanisms of gas sterilization. During the early part of this century, it was discovered that the terminal gas sterilization of sick rooms with formaldehyde was not as important as previously thought, and the emphasis on gas sterilization in the medical field declined. With the advent of modern medical science and its plastics, electronics, disposables, and other heat-labile components, a new interest has developed in gaseous sterilization procedures for the medical field. Several gaseous agents have been used successfully to sterilize medical devices, instruments, and equipment. However, these agents can be toxic to people as well as the microorganism they are designed to destroy, and caution is needed to ensure appropriate protection of personnel and patients from exposure to many of these gaseous sterilants. Ethylene Oxide Phillips and Kaye (12), in a series of reports, reviewed the early literature concerning the use of ETO as a bactericidal agent. They proposed an alkylation reaction as the mechanism of action of this material and established the basic conditions under which ETO was most effective as a sterilizing agent. This was the beginning of a new era in the field of medical device sterilization. The development of ETO sterilization methods and procedures, pioneered by Phillips and Kaye and continued by numerous other investigators, has led to the widespread use of disposable equipment and supplies in the hospital industry. This trend has done much to decrease the possibility of cross-contamination and has aided in the battle against hospital-acquired infections. It has, however, also led to the discovery of the toxic effects of ETO, and the safety procedures for the use of this material must be carefully considered to avoid personnel, patient, and environmental exposure. ETO is a colorless gas that is highly reactive with many different types of chemicals. ETO gas is highly flammable and explosive. However, mixture of the gas with carbon dioxide (13) or other gaseous carriers (fluorocarbons) (14) significantly reduces the fire hazards associated with the pure substance and allows its use, in special vessels, for sterilization. Mixtures of ETO in fluorocarbons appear to be more advantageous for use in hospitals, but information on the potential environmental hazards of these compounds has limited their use (15, 16, 17). As was mentioned above, ETO mixtures have been used in sterilization processes. With the concern over fluorocarbons, processes have been developed using vacuum vessels in which a series of evacuations and backfills with nitrogen are used to ensure that the oxygen level remaining is insufficient to support combustion when pure ETO is added. The equipment used for the sterilization process is complex and has been developed to ensure appropriate mixing and control of the factors required (e.g., temperature, RH, ETO concentration) to achieve sterilization (18). Formaldehyde Formaldehyde has been shown, under appropriate conditions of temperature and humidity, to be both sporicidal and bactericidal. Although the use of formaldehyde in the decontamination of sick rooms in hospitals was considered helpful in the early part of this century, further study of the practice indicated that such a drastic method was not necessary to ensure cleanliness of rooms occupied by contagious persons. However, formaldehyde is still used as a fumigant for rooms and buildings in which massive contamination has occurred, such as mold growth in water-damaged buildings and in the terminal decontamination of high-containment biologic laboratories. It is the sterilizing gas of choice for decontamination of biologic safety cabinets and high-efficiency particulate air (HEPA) filter units. Formaldehyde is generated by heating either paraformaldehyde or formalin to release the gaseous formaldehyde, and the activity of the formaldehyde depends on its condensation on contaminated surfaces. A procedure for microbiologic decontamination using paraformaldehyde has been published by the National Sanitation Foundation International (19). Formaldehyde has also been demonstrated to be toxic to humans and has been classified as a potential carcinogen. The Occupational Safety and Health Administration (OSHA) has thus developed a standard regarding potential personnel exposure (20). Anyone using this material would be wise to review current federal and state regulations that might apply to both personnel exposure and environmental release. Low-Temperature Steam Formaldehyde Process Although pure formaldehyde has not been found to be particularly useful for medical device sterilization in the United States, European investigators have demonstrated that a combination of low-temperature steam and formaldehyde (LTSF) can be used. This process was first described by Alder et al. (21) in England. It was initially designed for the processing of cystoscopes and similar devices. Since that time, equipment has been developed that provides the necessary controlled conditions for sterilization of a wide variety of medical devices. Kanemitsu et al. (22) evaluated an LTSF sterilizer and concluded that this methodology was particularly useful because of its excellent efficacy, short handling time, and safety. However, these authors warned that the size of the load in the sterilizer affected its efficacy and that small loads were preferable to larger ones for processing. The process involves the injection of dry formaldehyde gas into the treatment vessel followed by injection of steam to ensure an internal temperature of about 73ВC and a holding time of 2 hours. The process is completed, and the residual formaldehyde is removed by further steam flushes and an introduction of sterile filtered air (23). As with ETO sterilization, the potential for residual formaldehyde on the surface of sterilized devices is a major concern. Nystrom (24) reported that studies in Sweden have shown that residual formaldehyde can consistently be kept under 5 mg/cm3. Nystrom also stated that the occupational exposure resulting from the operation of this process is well below the threshold limit value of 0.6 mg/m3 mandated by Swedish occupational health regulations. Proponents of the process point to the facts that treated equipment needs less aeration than ETO does and that the in P.1528 creased temperature of operation increases the probability of sterilization success. In the U.S., however, this process has not been well accepted, probably because a reliable commercial process has not been validated, and there is considerable concern regarding the toxic and allergenic nature of formaldehyde. Alternatives to Ethylene Oxide Sterilization Concern over the hazards associated with the use of ETO have prompted many investigators to evaluate alternative methods for sterilizing heat-labile devices and instruments, including vapor phase hydrogen peroxide (VPHP) and various gas plasma technologies. Although not yet in widespread use, these technologies are beginning to be evaluated by healthcare facilities as safer more environmentally friendly alternatives to ETO processes. Vapor Phase Hydrogen Peroxide Liquid hydrogen peroxide (H2O2) has long been known for its ability to sterilize and its relative safety. Graham and Rickloff (25) reported on the development of a process using gaseous H2O2 at low concentrations and ambient temperatures to sterilize equipment and devices. It appears that sterilization can be achieved with this material with relatively short contact times. One of the major concerns of using relatively powerful oxidants for sterilizing medical devices has been the potential for damage to the devices. The short contact times required for the vapor phase H2O2 process appear to allow for reduced potential damage to devices because of possible oxidation. Vapor phase H2O2 technology seems to have considerable potential in its use to replace ETO for the sterilization of heat-labile materials. Johnson et al. (26) and Klapes and Vesley (27) reported that VPHP generators have shown sporicidal activity and that, in their studies, the process shows promise as an effective and safe alternative method of sterilization. However, much work is still to be done with regard to such factors as compatibility studies and efficacy. In addition, the penetrability of H2O2 vapor through cellulosics is limited by absorption, which further limits the type of packaging available for this process. Nonetheless, VPHP sterilization is a promising alternative to more toxic and potentially environmentally hazardous methods of sterilization. Plasma Gas Sterilization Other alternatives to ETO sterilization have been developed and are currently available for use in healthcare facilities for the processing of heat-sensitive devices. These low-temperature plasma technologies include the Plaslyte (AbTox, Mundelein, IL) system that uses gaseous peracetic acid and the Sterrad (Advanced Sterilization Products, Irvine, CA) system that uses low-temperature H2O2 gas plasma (LT-HPGP). The ion plasma sterilization processes operate at relatively low temperatures by exposing peracetic acid or H2O2 to either strong electric or magnetic fields. Such exposure results in the formation of an ion plasma that contains reactive radicals that are known to be reactive with almost all molecules essential for metabolism and reproduction of living cells (e.g., DNA, RNA, proteins, etc.). These technologies have stimulated interest in healthcare facility personnel, because they have short turnaround times compared with ETO sterilizers and are both more environmentally friendly and safer to use. Rutala and Weber (28) summarized the disadvantages of these methodologies. The authors stated that the use of the peracetic acid plasma method was limited to stainless steel surgical instruments (excluding lumen devices and hinged instruments). In addition, no liquids or materials that might be harmed by vacuum could be treated. The LT-HPGP process was limited by U.S. Food and Drug Administration (FDA) restrictions on treatment, by this method, of endoscopes and other medical devices with lumina longer than 12 inches or having a lumen diameter less than one-quarter inch (6 mm). Cellulose, linens, and liquids also cannot be processed in this device. Finally, the LT-HPGP process requires special packaging of devices and a special tray for processing. A number of studies have demonstrated the efficacy of the LT-HPGP against viruses and parasites in the laboratory (29, 30). The efficacy of both processes in the treatment of medical devices was evaluated by comparison with the ETO 12/88 process by Alfa et al. (31). These authors concluded that the margin of safety for the methods tested was less than that of the 12/88 method and were concerned that even the 12/88 method failed to kill microorganisms in narrow lumen devices when salt or serum was present. They emphasized the need for scrupulous cleaning of the lumen of medical devices before treatment to ensure sterilization. Such research emphasizes the need for strict adherence to cleaning protocols before treatment of devices and provides valuable insight into a number of problems that can be associated with any alternative sterilization techniques. Bar et al. (32), concerned about reports of mycobacterial contamination of bronchoscopes, studied the use of LT-HPGP for the sterilization of these devices. Their results indicated that bronchoscopes washed and disinfected by conventional “washer/disinfector” as well as “intensive washing” (washing followed by glutaraldehyde treatment) still showed the presence of mycobacterium DNA, by nucleic acid amplification technique. Those scopes sterilized by the LT-HPGP were all negative by this test methodology. The authors concluded that LT-HPGP sterilization would be recommended if the nucleic acid amplification technique was to be used for the diagnostic procedure to verify sterility of the treated bronchoscopes. Feldman and Hui (33) studied the compatibility of LT-HPGP sterilization with various medical devices and materials. The authors reported that in their studies of over 600 individual resterilizable devices from more than 125 manufacturers, approximately 95% of the devices could be safely sterilized by this process. They listed various materials that could be considered for LT-HPGP processing, including stainless steel (300 series), aluminum (600 series), titanium, glass, silica ceramic, and a number of plastics and elastomers. They also studied numerous adhesives and provided a listing of the adhesives that proved to be most compatible with the process. Although these alternative methods have been developed in response to the patient, occupational, and environmental safety hazards associated with the use of ETO sterilizers, they may not themselves be without potential hazard. A recent report of several cases of corneal endothelial decompensation resulting from sur P.1529 gery with instruments sterilized in the peracetic acid plasma system has raised questions about the possible interaction of the sterilizing agents with the brass-containing parts of the instruments, resulting in release of metal compounds that can cause corneal decompensation. Studies are currently underway to verify the connection between the sterilization process and the injuries (34). Ikarashi et al. (35) also reported on the cytotoxicity of various medical materials exposed to a VPHP sterilization process, thus emphasizing the requirement for further investigation regarding the need for aeration to remove cytotoxic residuals from materials treated by the alternative techniques. IONIZING RADIATION Although ionizing radiation is not commonly used in the hospital for the sterilization of equipment and medical devices, it is an important process in the manufacture and packaging of devices used in the healthcare facility. Many of the devices that are supplied sterile to the hospital, such as plastic hypodermic syringes and catheters, are formulated to be sterilized by gamma radiation and may be damaged or may not properly function when sterilized in any other manner. These items are considered to be single-use items and are not to be resterilized once they have been opened and contaminated, unless the manufacturer guarantees the safety of the device after resterilization (see Chapter 87). Radiation causes little or no damage to the materials treated and leaves no residual radioactivity. Radiation of drugs, pharmaceuticals, and tissues for transplantation has also been successful. Although there are a number of proposals for explaining the radiation inactivation of microorganisms, the effect of radiation appears to be a result of damage to DNA. Resistance to radiation treatment appears to depend on the microorganism's ability to repair the DNA damage (36, 37). As with other sterilization processes, it has been generally accepted that bacterial spores are the most resistant microorganisms, and that demonstration of the killing of spores is an appropriate demonstration of the efficacy of the radiation sterilization process. It appears that although bacterial spores are the most resistant and gram-negative rods appear to be the least resistant to radiation damage, a number of inherently radiation-resistant microorganisms do exist and could be present in or on items to be sterilized. Members of the genus Deinococcus appear to be extremely resistant to radiation (38). In addition, other microorganisms (specific Moraxella, Arthrobacter, Acinetobacter, and Pseudomonas species) have been shown to exhibit enhanced resistance to radiation damage. Procedures for ensuring the sterility of irradiated products have been proposed by the Association for the Advancement of Medical Instrumentation (39). These procedures are based on the known bioburden of the product, dose of irradiation, and good manufacturing procedures as required by the FDA. FILTRATION Although filtration is an important process in the preparation of a variety of liquid products used in the healthcare facility, in general it cannot be considered a mechanism for sterilization. Strict interpretation of the term sterilization implies killing or removal of all forms of life. Filters in use for the sterilization of such items as intravenous additives, drugs, and vaccines are, for the most part, bacterial filters. They do not, nor are they designed to, remove viruses. On the other hand, the materials that are treated by filtration are not expected to have live virus in them. Still, the fact that this process is designed for removal of bacteria must be considered. Processing of fluids in the healthcare setting is discussed by Eudailey (40). Procedures for ensuring the quality of filtered materials, with particular reference to hospital pharmacy prepared intravenous fluids and hyperalimentation fluids, are presented in a number of articles on the subject (41, 42, 43, 44). The type of filter to be used for a particular operation depends on the operation and the requirements for the final product. Different types of filters are used for specific processes. The filter media range from deep filters of various materials (e.g., fiberglass, cotton, resins, porcelain, diatomaceous earth) to membrane filters of cellulose and other polymers. Depth filters have the advantage of being able to handle large amounts of contaminants throughout their thickness and can often retain particles smaller than their normal size rating because of adsorption of the particles on the filter. These filters, however, have some disadvantages. They tend to allow media migration in that the filter media may be released and travel through the filter and in fact may contaminate the product. There may also be a release of microorganisms as material passes through the filter during long process times. The filters may also retain significant amounts of fluid product, which can be a problem if the product is particularly valuable. Membrane filters, on the other hand, do not suffer from the problems of media migration or potential release of filtered microorganisms. They are efficient, and there is no retention of fluid product. The major disadvantage of the membrane filter is the fact that it tends to get clogged by excess dirt in the system. It should be noted that filtration is also important in the removal of microorganisms and particulates from gases and air. The filtration capacity of such filters primarily depends on impaction, diffusion, and electrostatic charge. Particles traveling in an air stream tend to stay in that stream. Filtration is accomplished when the particles in the air stream have an impact on the surface of the filter fibers. The higher the air velocity, the greater the surface area of the filter, and the smaller the diameter of the fibers, the higher the probability of impaction. Diffusion also plays a part in the filtration process. Low-velocity air flow favors diffusion of the particulates to the filter surface, and very small (low-mass) particles tend to diffuse in the depths of the filter and are intercepted by the filter. HEPA filters have an efficiency of at least 99.97% at 0.3Вm. These filters, by design, are more efficient for particle sizes above and below 0.3 Вm. Laminar-flow HEPA filtration units have been suggested for operating rooms, isolation rooms, and laboratories. It should be noted that at the point of release from the filters, the air is sterile, but as with any other sterilization process, the air quickly becomes contaminated from contact with unsterile materials. The use of these units should be tempered with an understanding of their limitations and the potential for recontamination of the air. It should also be noted that the filters used to remove infec P.1530 tious agents from the air are considered to be contaminated with those infectious agents. Personnel charged with maintenance, testing, and removal of the filters should be appropriately cautioned with regard to the hazards involved with these procedures. PASTEURIZATION Pasteurization is a process of inactivation of the vegetative cells of pathogenic bacteria and of viruses by heating at relatively low temperatures. The process has found widespread use in the food industry since its development by Louis Pasteur. The actual time/temperature conditions for pasteurization vary with the type of material being treated and the personnel performing the process. Historically, pasteurization for milk involves heating to approximately 60ВC for 30 minutes or to 70ВC for 15 to 20 seconds. Anesthesia equipment has been pasteurized by using an exposure to hot water at 75ВC for 10 minutes (45). Treatment of plasma fractions at 60ВC for 6 hours has been used for inactivation of viruses in the production of blood products (46). All these processes use the principle of heat inactivation of vegetative cells and viruses to ensure appropriate kill times. The major disadvantages of pasteurization in the treatment of critical materials is the lack of standardization of the equipment and difficulty of validation. Because this is not a sterilization process, extreme care must be taken to ensure that the process is performed so that agents considered to be particularly important are inactivated. VALIDATION Major research studies on sterilization indicate that there is more to be learned with regard to sterilization processes (2, 3). Research in the laboratory has been directed at the mechanisms of action of various sterilization processes, and the results have been conflicting, because there is so much variation in the conditions of the studies. Although much has been learned, the information gained is not always directly applicable to the real-world process in that microorganisms are not the same and conditions with regard to composition of loads, organic load, and bioburden are constantly changing. Therefore, any validation process must consider the variability inherent in the process and demonstrate overkill if sterilization is to be ensured. Historically, the spores of bacteria have been thought to be the most resistant microorganisms with regard to heat, radiation, and chemicals. It has been natural to assume that processes that result in inactivation of these spores would provide a significant margin of safety to ensure sterility of the products treated by these processes. Spore suspension testing requires specific laboratory procedures and considerable incubation time. Alternative chemical indicators have been developed and compared with spore tests with good results (47), but spore testing continues to be the standard. Although indicators are an important part of quality assurance of sterilization processes, the validation of the process and documentation of the actual operating parameters of the process are of paramount importance. It should be noted that spore and chemical indicators testing can only be as good as the placement of the spore suspensions or indicators. Failure to place the indicators in appropriate places in the load leads to false-negative results (i.e., apparent sterility when the items are not really sterilized). All sterilization processes should be thoroughly evaluated before being put into service and at regular intervals. Autoclaves should be mapped with thermocouples to determine potential cold spots. Filter systems should be tested for leakage. Gas sterilization units should be appropriately validated for such factors as gas concentration, temperature, and RH. The sterility assurance level for a particular sterilization process is not routinely determined in the healthcare facility, because personnel lack expertise in the procedures. Young (48) has discussed cycle times and safety factors for steam and ETO sterilization cycles to be used in hospitals. Validation of healthcare facility sterilization equipment is primarily performed by the manufacturer of the equipment. To ensure appropriate sterilization processes, healthcare facility personnel must ensure that all manufacturer recommendations are met. The daily operation of the sterilizing processes must be documented by personnel performing the process. This documentation should be reviewed for each operation, and any malfunction should be noted and appropriate action taken to ensure that the product either has been properly treated or is returned for reprocessing. In light of the advent of new medical devices, intricately designed with heat-sensitive parts and narrow lumina, the mechanisms for appropriate sterilization become a matter of concern for patient safety. In a provocative editorial, Rutala and Weber (28) questioned whether or not, because of the development of low-temperature sterilization technologies, there is a need to redefine sterilization. Current FDA requirements stipulate that a sterilizer's microbicidal performance must be tested under specified simulated use conditions, which include that the test articles must be inoculated with 106 colony-forming units (CFU)/unit of the most resistant test microorganism prepared with inorganic and organic test loads. The inocula must be placed in various locations on the test articles, including those least favorable to penetration and contact with the sterilant (49). Rutala and Weber, however, argue that these requirements may be too restrictive and that the requirements for efficacy should include the demonstration by instrument/device manufacturers that cleaning followed by a sterilization process can inactivate a clinically relevant inoculum of highly resistant microorganisms in the presence of an organic load in the most inaccessible location in the device. They note that the responsibility for defining the efficacy of new sterilization technologies should be met by the FDA, the device manufacturer, or the sterilizer manufacturer. It seems logical that medical device manufacturers should take the lead in the evaluation of new sterilization processes for their own devices and that they should recommend the safest, most environmentally friendly, and cost-effective technologies available. Healthcare personnel must be aware of the problems associated with new and existing technologies and ensure that whatever process is used, it will be safe and effective. MATERIALS DEGRADATION New methodologies always bring with them new benefits as well as new potential hazards. New sterilization technologies are P.1531 no exception. The benefits of new technologies must be reviewed and verified so that decisions can be made regarding the efficacy of medical devices as related to the sterilization process. Nuutinen et al. (50) studied the effect of various sterilization processes on the physical and mechanical properties of self-reinforced bioabsorbable fibers made out of polylactide (PLLA). The intrinsic viscosity, crystallinity, and mechanical properties (modulus of elasticity, yield strength, and ultimate tensile strength) were tested before and immediately after each sterilization treatment, as well as up to 30 weeks in vitro. Compared with unsterilized fibers, the intrinsic viscosity was markedly decreased after radiation sterilization (gamma and electron beam), and the loss in mechanical properties was accelerated during in vitro degradation. Plasma and ethylene oxide (one and two cycles) did not markedly alter the properties of the samples after sterilization or during in vitro degradation. The authors concluded that their data are important for determining the effect of various sterilization processes on the physical and mechanical properties of polylactide-based materials and can be used to predict how fast degradation of the mechanical properties of the self-reinforced PLLA will occur. They can also be used to tailor the degradation kinetics to optimize implant design. With the advent of new medical devices that are heat sensitive, the search for a safe, effective sterilization methodology that is compatible with the device materials has accelerated. Although the use of various oxidizing agents, coupled with ionization procedures (as in LT-HPGP), or VPHP generators have become more popular and are replacing the more toxic ETO processes, there are potential problems with the integrity of the materials treated by these processes. Hopper et al. (51) postulated that conventional polyethylene liners cross-linked by sterilization with gamma radiation in air had better in vivo wear performance than non–cross-linked liners sterilized with gas plasma. The polyethylene liners that had been sterilized with gamma radiation in air had a significantly lower wear rate than did the gas-plasma–sterilized liners. The authors concluded that in vivo wear of conventional polyethylene liners that had been sterilized with gamma radiation in air was, on average, 50% less than that of non–cross-linked liners sterilized with gas plasma. In a comprehensive study of the safety of plasma-based sterilization, Lerouge et al. (52) used both the Sterrad and Plazlyte processes to evaluate the induction of surface modifications on polymeric medical devices. They observed surface oxidation and wettability changes on all surfaces sterilized by these techniques. The type and severity of the modification varied with the sterilizer and the type of polymer sterilized. It should be noted that these observed changes have not been shown to be particularly detrimental to patients, but further studies need to be performed to ensure the safety of this technology. NOSOCOMIAL INFECTIONS Sterilization and disinfection processes for medical devices and equipment have been developed specifically to prevent infections due to contamination of these materials. Obviously, if a material has been sterilized and is kept from being contaminated before use, there is no chance of infection in a patient exposed to it. Failure to appropriately perform or monitor the sterilization process or unvalidated changes in equipment or product, however, may result in an unsterilized product. Bryce et al. (53) reported on an outbreak of Bacillus cereus in intensive care unit patients on respirators. The infections were traced to ventilator circuitry that had been pasteurized. The infections were due to the presence of a spore-forming microorganism, and the method for treatment of the equipment was not sufficient to kill the spores of the offending microorganism. A similar outbreak involving Flavobacterium meningosepticum was reported by Pokrywka et al. (54). In this outbreak, it was discovered that the pasteurization units were operating at suboptimal temperatures, thus allowing survival of the microorganisms. Kaczmarek et al. (55) studied disinfection/sterilization practices for endoscopes in healthcare facilities and reported that the disinfection/sterilization procedures are not always optimal and that variation occurred even within hospitals. Pattison et al. (46) reported on an outbreak of hepatitis B associated with transfusion of commercially prepared plasma protein fraction that had undergone pasteurization in the preparation process. Nineteen of 31 patients receiving the plasma fraction had developed illness compatible with hepatitis B. The plasma had been subjected to treatment at 60ВC for 10 hours, but the authors suggest that the process was inadequate to destroy the hepatitis B virus. Although the study of Kaczmarek et al. concentrated on disinfection procedures and a number of outbreaks of nosocomial infection have been traced to inadequately disinfected materials and devices, few cases of nosocomial infection have been traced specifically to failure of sterilization processes. The notable exceptions are the outbreaks of nosocomial sepsis that have been traced to commercial intravenous fluids. Duma et al. (56) reported an outbreak of septicemias specifically related to intravenous infusions in 1971. Goldmann et al. (57) reported a nationwide outbreak of Enterobacter and Erwinia (Enterobacter agglomerans) infections traceable to commercial intravenous fluids that occurred in 1971. Goldmann et al. suggested that appropriate surveillance data were available before the dates of the outbreak and were sufficient to predict that there was a problem and that proper analysis of the data could have prevented the outbreak. In 1981, a second outbreak of nosocomial Enterobacter infections was traced to contaminated commercial intravenous fluids (58). During this outbreak, the contamination was shown to be present in the screw caps of bottles. The contamination was apparently protected from coming in contact with steam during the sterilization cycle by the design of the cap and thus was not subject to appropriate sterilizing conditions. These outbreaks point to the need for constant attention to detail with regard to ensuring the effectiveness of sterilization cycles and to review of surveillance data with particular regard to infections with exotic microorganisms associated with apparently sterile devices and fluids. HEALTH AND SAFETY Sterilization processes are designed, by definition, to eliminate all forms of life. As a result, these processes are inherently hazardous to those personnel involved with them. It is impera P.1532 tive that personnel understand the hazards of the process that they are required to perform. They must be trained in the use of appropriate personal protective equipment and understand and be able to carry out emergency procedures that would minimize personnel exposure to the sterilization process. Table 86.1 shows some of the potential hazards associated with major sterilization processes and includes reference to the OSHA standards that specifically apply. It is obvious that the hazards of sterilization processes involve both potential physical hazards such as heat and radiation and potential exposures to chemically hazardous materials such as the sterilant gases and their carriers. The administrative and supervisory personnel of each facility must recognize the hazards associated with the processes being performed in that facility, must develop appropriate safety procedures to protect the personnel involved, and must ensure that those procedures are being followed. TABLE 86.1. POTENTIAL OCCUPATIONAL HAZARDS ASSOCIATED WITH MAJOR STERILIZATION PROCESSES Ethylene Oxide Safety A number of reports have demonstrated the dangers of ETO to both patients and personnel. Both human and animal studies suggest that ETO is a potential occupational carcinogen, causing leukemia and other cancers. ETO has also been linked to reproductive damage, including spontaneous abortions, cytogenetic damage, neurologic effects ranging from nausea and dizziness to peripheral paralysis, and tissue irritation (59). OSHA has issued a standard (60) that sets a limit on worker exposure to ETO averaged over an 8-hour day. The standard was amended in 1988 to further reduce the health risk associated with ETO by requiring control of short-term exposures as well. The key provisions of the ETO standard include a limit on workplace exposure of one part ETO per million parts air (1 ppm) averaged over an 8-hour day, and an excursion limit of 5 ppm averaged over a sampling period of 15 minutes. Employee rotation is prohibited as a means of compliance with the excursion limit. Where the excursion limit is exceeded, employers must do the following: Use engineering controls and work practices to reduce exposure. These controls and practices may be supplemented by the use of respirators where necessary. Establish and implement a written compliance program to achieve the excursion limit. Establish exposure monitoring and training programs for employees subjected to ETO exposure above the excursion limit. Identify as a regulated area any location in which airborne concentrations of ETO are expected to exceed the excursion limit. Place warning labels on containers capable of releasing ETO to the extent that an employee's exposure would foreseeably exceed the excursion limit. Respirators can be used to control exposure only until feasible engineering and work practice controls are being implemented; during maintenance, repair, and other operations for which engineering controls are not feasible; in work situations wherein feasible engineering and work practice controls do not reduce exposures below the permissible exposure limit; and in emergencies. OSHA has set an action level of 0.5 ppm. If the 8-hour time-weighted airborne concentration of ETO is at or exceeds the action level, employers must begin periodic exposure monitoring and medical surveillance. Employers who demonstrate that worker exposures are below the action level need not comply with most provisions of the standard. If employers have not monitored worker exposures within the past year, they must do so for each job classification in a work area during each shift; representative sampling is permitted under certain circumstances. The frequency of subsequent monitoring depends on the results of the initial sampling. All monitoring may be observed by workers and their designated representatives. A comprehensive medical surveillance program must be conducted by or under the supervision of a licensed physician. Workers must receive a medical examination before assignment to an area in which exposure is at or above the prescribed level, annually if they are exposed at this level for 30 days or more during the year, upon request if they develop symptoms suggesting overexposure or want medical advice concerning the effects of ETO exposure on their ability to produce a healthy child, and when they end employment in an area of exposure. Other requirements include identification of excessive exposure areas, communication of hazard to affected employees, and OSHA record keeping. Patient Safety Because of the potential toxicity and resultant hazard to patients, it is important for persons using ETO for sterilization of medical devices to ensure adequate aeration for treated materials. The aeration process reduces ETO residues in and on the devices P.1533 to a level that will not cause problems for patients or personnel exposed to the treated materials. Formaldehyde Safety Studies indicate that formaldehyde is a potential human carcinogen (20). Airborne concentrations above 0.1 ppm can cause irritation of the eyes, nose, and throat. The severity of irritation increases as concentrations increase; at 100 ppm, exposure to formaldehyde is immediately dangerous to life and health. Dermal contact causes various skin reactions, including sensitization, which might force sensitized persons to find other work. To protect workers exposed to formaldehyde, the OSHA formaldehyde standard (61) applies to formaldehyde gas, its solutions, paraformaldehyde, and a variety of other materials that serve as sources of the substance. In addition to setting permissible exposure levels and exposure monitoring and training, the standard requires medical surveillance and medical removal of sensitized personnel, record keeping, regulation of potentially hazardous areas, hazard communication, and emergency procedures. Employers are to ensure primary reliance on engineering and work practices to control exposure. Selection and maintenance of appropriate personal protective equipment by employers is also required. If respirators are necessary, compliance with the OSHA respiratory protection standard is required. In addition, training is required at least annually for all employees exposed to formaldehyde concentrations of 0.1 ppm or greater. The permissible exposure limit for formaldehyde in all workplaces covered by the OSHA Act is 0.75 ppm measured as an 8-hour time-weighted average. The standard includes a 2 ppm short-term exposure limit (STEL) (i.e., maximum exposure allowed during a 15-minute period). The action level is 0.5 ppm measured over 8 hours. As with the ETO standard, the formaldehyde standard requires that the employer conduct initial monitoring to identify all employees who are exposed to formaldehyde at or above the action level or STEL and to accurately determine the exposure of each employee so identified. If the exposure level is maintained below the STEL and the action level, employers may discontinue exposure monitoring until such time as there is a change that could affect exposure levels. The employer must also monitor employee exposure promptly upon receiving reports of formaldehyde-related signs and symptoms. A medical removal protection provision is included in the standard for employees suffering significant adverse effects from formaldehyde exposure. This provision requires that such employees are removed to jobs with less exposure until their condition improves, or for a period of 6 months, or until a physician determines that they will not be able to return to any workplace with formaldehyde exposure. Occupational Safety and Health Administration Hazard Communication The hazard communication standard (62) requires identification and appropriate labeling of all hazardous chemicals in the workplace. This standard also requires appropriate training and medical monitoring of personnel. In addition to the general requirements of the hazard communication standard, other standards for specific hazardous chemicals also require certain labeling. The formaldehyde standard specifically delineates requirements for labeling of formaldehyde, including mixtures and solutions composed of 0.1% or greater formaldehyde and for materials capable of releasing formaldehyde in excess of 0.1 ppm. Hazard labeling, including a warning that formaldehyde presents a potential cancer hazard, is required where formaldehyde levels, under reasonably foreseeable conditions of use, could exceed 0.5 ppm. The ETO standard also has provisions for labeling containers that might release substantial quantities of ETO in excess of the excursion limits set by the standard. Environmental Safety In addition to the potential for personnel exposure, environmental concerns must be addressed. This is particularly true for the release of agents such as ETO and formaldehyde. The carrier for ETO may also be a potential environmental hazard, because the chlorinated and fluorinated hydrocarbons that have historically been used as a carrier to minimize the explosiveness of the ETO have been banned. These agents can be toxic in the environment and are regulated by either federal or state regulations concerned with toxic releases to air and water. It is important to realize that such environmental regulations are constantly being evaluated and revised by the regulatory sector, and specific references to such regulations in any textbook would undoubtedly be dated. It should be sufficient to warn that administrative and supervisory personnel must evaluate the release of these materials from the facility with regard to specific applicable regulations. REFERENCES 1. Block SS. Historical review. In: Block SS, ed. Disinfection, sterilization, and preservation. Philadelphia: Lea & Febiger, 1991:1–17. 2. Wickamanayake GB, Sproul OJ. Kinetics of the inactivation of microorganisms. In: Block SS, ed. Disinfection, sterilization, and preservation. Philadelphia: Lea & Febiger, 1991:72–84. 3. Pflug IJ, Holcomb RG. Principles of thermal inactivation of microorganisms. In: Block SS, ed. Disinfection, sterilization, and preservation. Philadelphia: Lea & Febiger, 1991:85–131. 4. Joslyn LJ. Sterilization by heat. In: Block SS, ed. Disinfection, sterilization, and preservation. Philadelphia: Lea & Febiger, 1991:495–526. 5. Pflug IJ. The role of water in heat sterilization. Pharmaceut Manufact 1984;August:16–17. 6. Rutala WA, Stiegel M, Sarubbi F Jr. Decontamination of laboratory microbiological waste by steam sterilization. Appl Environ Microbiol 1982;43:1311–1316. 7. Association for the Advancement of Medical Instrumentation. Good hospital practice: steam sterilization and sterility assurance. Recommended practice. Arlington, VA: AAMI, 1988. 8. Howard WJ. The controversy of flash sterilization. Today's OR Nurse 1991;January:24–27. 9. Reich R, Fitzpatrick B. Flash sterilization. J Hosp Suppl Process Distrib 1985;May/June:60–63. 10. Garner J, Favero M. CDC Guidelines for the prevention and control of nosocomial infections guideline for handwashing and hospital environmental control. Am J Infect Control 1986;14:110–129. P.1534 11. Bruch CW. Dry-heat sterilization for planetary-impacting spacecraft. Proceedings of the National Conference on Spacecraft Sterilization Technology, NASA SP-108, 1996. 12. Phillips CR, Kaye S. Sterilizing action of gaseous ethylene oxide. I. Review. Am J Hyg 1949;50:270–279. 13. Coward H, Jones G. Limits of flammability of gases and vapor. Bureau of Mines Bulletin No. 503, 1952. 14. Kaye S. Non-inflammable ethylene oxide sterilant. U.S. Patent No. 2,891,838, 1959. 15. Environmental Protection Agency. U.S. EPA assessment of ethylene oxide as a potentially toxic air pollutant. October 2, 1985. Fed Reg 1985;50:40286. 16. Environmental Protection Agency. U.S. EPA protection of stratospheric ozone. August 12, 1986. Fed Reg 1986;53:30566. 17. Environmental Protection Agency. Protection of stratospheric ozone. April 3, 1989. Fed Reg 1989;54:13502. 18. Parisi A, Young W. Sterilization with ethylene oxide and other gases. In: Block SS, ed. Disinfection, sterilization, and preservation. Philadelphia: Lea & Febiger, 1991:580–595. 19. National Sanitation Foundation. Class II (laminar flow) biohazard cabinetry, NSF 49 1992. NSF International Standard, 1992. 20. U.S. Dept. of Labor. OSHA formaldehyde standard. 29 CFR 1910:1048. 21. Alder V, Brown A, Gillespie W. Disinfection of heat sensitive material by low temperature steam and formaldehyde. J Clin Pathol 1966;19:83–89. 22. Kanemitsu K, Kunishima H, Imasaka T, et al. Evaluation of a low-temperature steam and formaldehyde sterilizer. J Hosp Infect. 2003;55(1):47–52. 23. Ayliffe GAJ. The use of ethylene oxide and low temperature steam/formaldehyde in hospitals. Infection 1989;17:109–110. 24. Nystrom B. New technology for sterilization and disinfection. Am J Med 1991;91(suppl 3B):264S–266S. 25. Graham GS, Rickloff J. The feasibility of terminally sterilizing heat sensitive products with hydrogen peroxide gas. Presented at the fall meeting of the Parenteral Drug Association, San Francisco, CA, November, 1992. 26. Johnson J, Arnold J, Nail S, et al. Vaporized hydrogen peroxide sterilization of freeze dryers. J Parenter Sci Technol 1992;46:215–225. 27. Klapes NA, Vesley D. Vapor phase hydrogen peroxide as a surface decontaminant and sterilant. Appl Environ Microbiol 1992;56:503–506. 28. Rutala W, and Weber D. Low-temperature sterilization technologies: do we need to redefine sterilization? Infect Control Hosp Epidemiol 1996;17:87–91. 29. Vassal S, Favennec L, Ballet J, et al. Hydrogen peroxide gas plasma sterilization is effective against Cryptosporidium parvum oocysts. Am J Infect Control 1998;26:136–138. 30. Roberts C, Antonoplos P. Inactivation of human immunodeficiency virus type 1, hepatitis a virus, respiratory syncytial virus, vaccinia virus, herpes simplex virus type 1, and poliovirus type 2 by hydrogen peroxide gas plasma sterilization. Am J Infect Control 1998;26:94–101. 31. Alfa M, DeGagne P, Olson N, et al. Comparison of ion plasma, vaporized hydrogen peroxide, and 100% ethylene oxide sterilizers to the 12/88 ethylene oxide gas sterilizer. Infect Control Hosp Epidemiol 1996;17:92–100. 32. Bar W, Marquez de Bar G, Naumann A, et al. Contamination of bronchoscopes with Mycobacterium tuberculosis and successful sterilization by low-temperature hydrogen peroxide plasma sterilization. Am J Infect Control 2001:29(5):306–311. 33. Feldman L, Hui H. Compatibility of medical devices and materials with low-temperature hydrogen peroxide gas plasma. Med Device Diagn Ind December 1997. 34. Anonymous. Corneal decompensation after intraocular ophthalmic surgery—Missouri, 1998. MMWR 1998;47:306–309. 35. Ikarashi Y, Tsuchiya T, Nakamura A. Cytotoxicity of medical materials sterilized with vapour-phase hydrogen peroxide. Biomaterials 1995;16:177–183. 36. Davies R, Sinskey A, Botstein D. Deoxyribonucleic acid repair in a highly resistant Salmonella typhimurium. J Bacteriol 1973;114:357–366. 37. Town C, Smith K, Kaplan H. Production and repair of radiochemical damage in Escherichia coli deoxyribonucleic acid, its modification by culture conditions and relation to survival. J Bacteriol 1971;105:127. 38. Brooks BW. Red pigmented micrococci: a basis for taxonomy. Int J System Bacteriol 1980;30:627. 39. Association for the Advancement of Medical Instrumentation. Process control guidelines for radiation sterilization of medical devices. Arlington, VA: AAMI, 1981. 40. Eudailey W. Membrane filters and membrane-filtration processes for healthcare. Am J Hosp Pharm 1983;40:1921–1923. 41. Crawford S, Narducci W, Augustine S. National survey of quality assurance activities for pharmacy-prepared sterile products in hospitals. Am J Hosp Pharm 1991;48:2398–2413. 42. National Coordinating Committee on Large Volume Parenterals. Recommendations to pharmacists for solving problems with large volume parenterals. Am J Hosp Pharm 1976;33:231–236. 43. Levchuk J, Nolly R, Lander N. Method for testing the sterility of total nutrient admixtures. Am J Hosp Pharm 1988;45:1311–1321. 44. Akers M, Wright G, Carlson K. Sterility testing of antimicrobial-containing injectable solutions prepared in the pharmacy. Am J Hosp Pharm 1991;48:2414–2418. 45. Craig DB, Cowan S, Forsyth W, et al. Disinfection of anaesthesia equipment by a mechanized pasteurization method. Can Anaesth Soc J 1975;22:219–223. 46. Pattison CP, Klein C, Leger R, et al. An outbreak of type B hepatitis associated with transfusion of plasma protein fraction. Am J Epidemiol 1976;103:399–407. 47. Hirsch A, Manne S. Bioequivalent chemical steam sterilization indicators. Med Instrum 1984;18:272–275. 48. Young JH. Comparison of in-hospital and industrial sterilization of medical devices. J Health Care Mater Mgmt 1986;4:29–34. 49. Food and Drug Administration, Division of General and Restorative Devices. Guidance on premarket notification [510(K)] submissions for sterilizers intended for use in health care facilities. Washington, DC: FDA, March 1993. 50. Nuutinen JP, Clerc C, Virta T, et al. Effect of gamma, ethylene oxide, electron beam, and plasma sterilization on the behaviour of SR-PLLA fibres in vitro. J Biomater Sci Polym Ed. 2002;13(12):1325–36. 51. Hopper RH Jr, Young AM, Orishimo KF, et al. Effect of terminal sterilization with gas plasma or gamma radiation on wear of polyethylene liners. J Bone Joint Surg 2003;85A(3):464–468. 52. Lerouge S, Tabrizian M, Wertheimer M, et al. Safety of plasma-based sterilization: Surface modifications of polymeric medical devices induced by Sterrad and Plazlyte processes. Bio-Med Mat Eng 2002:12:3–13. 53. Bryce E, Smith J, Tweeddale M, et al. Dissemination of Bacillus cereus in an intensive care unit. Infect Control Hosp Epidemiol 1993;14:459–462. 54. Pokrywka M, Viazanko K, Medvick J, et al. A Flavobacterium meningosepticum outbreak among intensive care patients. Am J Infect Control 1993;21:139–145. 55. Kaczmarek RG, Moore R, McCrohan J, et al. Multi-state investigation of the actual disinfection/sterilization of endoscopes in health care facilities. Am J Med 1991;92:257–261. 56. Duma R, Warner J, Dalton H. Septicemia from intravenous infusions. N Engl J Med 1971;284:257–260. 57. Goldmann D, Dixon R, Fulkerson C, et al. The role of nationwide nosocomial infection surveillance in detecting epidemic bacteremia due to contaminated intravenous fluids. Am J Epidemiol 1978;108:207–213. 58. Matsaniotis N, Syriopoulou V, Theodoridou M, et al. Enterobacter sepsis in infants and children due to contaminated intravenous fluids. Infect Control 1984;5:471–477. 59. Keene JH. The mutagenicity, toxicity, and potential carcinogenicity of ethylene oxide. MPH thesis. Chapel Hill, NC: University of North Carolina, School Of Public Health, 1980:35. 60. U.S. Dept. of Labor. OSHA ethylene oxide standard. 29 CFR 1910:1047. 61. U.S. Dept. of Labor. OSHA formaldehyde standard. 29 CFR 1910.1048 62. U.S. Dept. of Labor. OSHA hazard communication standard. 29 CFR 1910:1200.
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Each year in the United States there are approximately 27,000,000 surgical procedures and an even larger number of invasive medical procedures (1). For example, there are at least 10 million gastrointestinal endoscopies per year (2). Each of these procedures involves contact by a medical device or surgical instrument with a patient's sterile tissue or mucous membranes. A major risk of all such procedures is the introduction of infection. Failure to properly disinfect or sterilize equipment carries not only the risk associated with breach of the host barriers but the additional risk of person-to-person transmission (e.g., hepatitis B virus) and transmission of environmental pathogens (e.g., Pseudomonas aeruginosa). Achieving disinfection and sterilization through the use of disinfectants and sterilization practices is essential for ensuring that medical and surgical instruments do not transmit infectious pathogens to patients. Since it is unnecessary to sterilize all patient-care items, healthcare policies must identify whether cleaning, disinfection, or sterilization is indicated based primarily on the items' intended use. Multiple studies in many countries have documented lack of compliance with established guidelines for disinfection and sterilization (3, 4, 5, 6). Failure to comply with scientifically based guidelines has led to numerous outbreaks (6, 7, 8, 9, 10). This chapter presents a pragmatic approach to the judicious selection and proper use of disinfection processes, based on well-designed studies assessing the efficacy (via laboratory investigations) and effectiveness (via clinical studies) of disinfection procedures. DEFINITION OF TERMS Sterilization is the complete elimination or destruction of all forms of microbial life and is accomplished in healthcare facilities by either physical or chemical processes. Steam under pressure, dry heat, ethylene oxide (ETO) gas, hydrogen peroxide gas plasma, and liquid chemicals are the principal sterilizing agents used in healthcare facilities. Sterilization is intended to convey an absolute meaning, not a relative one. Unfortunately, some health professionals as well as the technical and commercial literature refer to “disinfection” as “sterilization” and items as “partially sterile.” When chemicals are used for the purposes of destroying all forms of microbiologic life, including fungal and bacterial spores, they may be called chemical sterilants. These same germicides used for shorter exposure periods may also be part of the disinfection process (i.e., high-level disinfection). Disinfection describes a process that eliminates many or all pathogenic microorganisms on inanimate objects with the exception of bacterial spores. Disinfection is usually accomplished by the use of liquid chemicals or wet pasteurization in healthcare settings. The efficacy of disinfection is affected by a number of factors, each of which may nullify or limit the efficacy of the process. Some of the factors that affect both disinfection and sterilization efficacy are the prior cleaning of the object; the organic and inorganic load present; the type and level of microbial contamination; the concentration of and exposure time to the germicide; the nature of the object (e.g., crevices, hinges, and lumina); the presence of biofilms; the temperature and pH of the disinfection process; and, in some cases, the relative humidity of the sterilization process (e.g., ETO). By definition, then, disinfection differs from sterilization by its lack of sporicidal property, but this is an oversimplification. A few disinfectants kill spores with prolonged exposure times (3 to 12 hours) and are called chemical sterilants. At similar concentrations but with shorter exposure periods (e.g., 20 minutes for 2% glutaraldehyde), these same disinfectants kill all microorganisms with the exception of large numbers of bacterial spores and are called high-level disinfectants. Low-level disinfectants may kill most vegetative bacteria, some fungi, and some viruses in a practical period of time (в‰10 minutes), whereas intermediate-level disinfectants may be cidal for mycobacteria, vegetative bacteria, most viruses, and most fungi, but do not necessarily kill bacterial spores. The germicides differ markedly among themselves primarily in their antimicrobial spectrum and rapidity of action. Table 85.1 lists the methods of sterilization and disinfection. Table 85.2 lists the characteristics desired in an ideal disinfectant. TABLE 85.1. METHODS OF STERILIZATION AND DISINFECTION TABLE 85.2. PROPERTIES OF AN IDEAL DISINFECTANT Broad spectrum: should have a wide antimicrobial spectrum Fast acting: should produce a rapid kill Not affected by environmental factors: should be active in the presence of organic matter (e.g., blood, sputum, feces) and compatible with soaps, detergents, and other chemicals encountered in use Nontoxic: should not be harmful to the user or patient Surface compatibility: should not corrode instruments and metallic surfaces and should not cause the deterioration of cloth, rubber, plastics, and other materials Residual effect on treated surfaces: should leave an antimicrobial film on the treated surface Easy to use with clear label directions Odorless: should have a pleasant odor or no odor to facilitate its routine use Economical: should not be prohibitively high in cost Solubility: should be soluble in water Stability: should be stable in concentrate and use-dilution Cleaner: should have good cleaning properties Environmentally friendly: should not damage the environment on disposal Modified from 193. Cleaning, on the other hand, is the removal of visible soil (e.g., organic and inorganic material) from objects and surfaces, and it normally is accomplished by manual or mechanical means using water with detergents or enzymatic products. Thorough cleaning is essential before high-level disinfection and sterilization since inorganic and organic materials that remain on the P.1474 P.1475 surfaces of instruments interfere with the effectiveness of these processes. Decontamination is a procedure that removes pathogenic microorganisms from objects so they are safe to handle, use, or discard. The suffix -cide or -cidal indicates a killing action. For example, a germicide is an agent that can kill microorganisms, particularly pathogenic microorganisms (germs). The term germicide includes both antiseptics and disinfectants. Antiseptics are germicides applied to living tissue and skin, whereas disinfectants are antimicrobials applied only to inanimate objects. In general, antiseptics are used only on the skin and not for surface disinfection, and disinfectants are not used for skin antisepsis, because they may cause injury to skin and other tissues. Other words with the suffix -cide (e.g., virucide, fungicide, bactericide, sporicide, and tuberculocide) can kill the type of microorganism identified by the prefix. For example, a bactericide is an agent that kills bacteria (11, 12, 13, 14, 15, 16). A RATIONAL APPROACH TO DISINFECTION AND STERILIZATION Over 30 years ago, Earle H. Spaulding (12) devised a rational approach to disinfection and sterilization of patient-care items or equipment. This classification scheme is so clear and logical that it has been retained, refined, and successfully used by infection control professionals and others when planning methods for disinfection or sterilization (11, 13, 15, 17, 18). Spaulding believed that the nature of disinfection could be understood more readily if instruments and items for patient care were divided into three categories based on the degree of risk of infection involved in the use of the items. The three categories he described were critical, semicritical, and noncritical. This terminology is employed by the 1985 Centers for Disease Control and Prevention (CDC) in several of its guidelines: for handwashing and hospital environmental control (19), for the prevention of transmission of human immunodeficiency virus (HIV) and hepatitis B virus (HBV) to healthcare and public-safety workers (20), and for environmental infection control and prevention in healthcare facilities (21). Critical Items Critical items are so called because of the high risk of infection if such an item is contaminated with any microorganism, including bacterial spores. Thus, it is critical that objects that enter sterile tissue or the vascular system be sterile, because any microbial contamination could result in disease transmission. This category includes surgical instruments, cardiac and urinary catheters, implants, and ultrasound probes used in sterile body cavities. Most of the items in this category should be purchased as sterile or be sterilized by steam sterilization if possible. If heat-sensitive, the object may be treated with ETO, hydrogen peroxide gas plasma, or by liquid chemical sterilants if other methods are unsuitable. Table 85.1 lists several germicides categorized as chemical sterilants. These include в‰2.4% glutaraldehyde-based formulations, 0.95% glutaraldehyde with 1.64% phenol/phenate, 7.5% stabilized hydrogen peroxide, 7.35% hydrogen peroxide with 0.23% peracetic acid, 0.2% peracetic acid, and 0.08% peracetic acid with 1.0% hydrogen peroxide. Liquid chemical sterilants can be relied on to produce sterility only if cleaning, to eliminate organic and inorganic material, precedes treatment and if proper guidelines as to concentration, contact time, temperature, and pH are met. Semicritical Items Semicritical items are those that come in contact with mucous membranes or nonintact skin. Respiratory therapy and anesthesia equipment, some endoscopes, laryngoscope blades, esophageal manometry probes, rectal manometry catheters, and diaphragm fitting rings are included in this category. These medical devices should be free of all microorganisms, although small numbers of bacterial spores may be present. Intact mucous membranes, such as those of the lungs or the gastrointestinal tract, generally are resistant to infection by common bacterial spores but susceptible to other microorganisms such as bacteria, mycobacteria, and viruses. Semicritical items minimally require high-level disinfection using chemical disinfectants. Glutaraldehyde, hydrogen peroxide, ortho-phthalaldehyde (OPA), and peracetic acid with hydrogen peroxide are cleared by the Food and Drug Administration (FDA) and are dependable high-level disinfectants provided the factors influencing germicidal procedures are met (Table 85.1). When a disinfectant is selected for use with certain patient-care items, the chemical compatibility after extended use with the items to be disinfected also must be considered. Although the complete elimination of all microorganisms in/on an instrument with the exception of small numbers P.1476 of bacterial spores is the traditional definition of high-level disinfection, the FDA requires a more defined end point. For example, the FDA accepts a 6-log10 reduction of microorganisms (i.e., specific strains of mycobacteria), with the exception of small numbers of bacterial spores, as proof of high-level disinfection. This is noteworthy, as complete elimination of microorganisms (e.g., Mycobacterium chelonae) on a contaminated instrument occurs with a starting inoculum of в‰106 colony-forming units (CFU) but may not occur if the starting inoculum is >106 CFU. However, cleaning followed by high-level disinfection should eliminate sufficient pathogens to prevent transmission of infection (22, 23). Laparoscopes and arthroscopes entering sterile tissue ideally should be sterilized between patients. However, they sometimes undergo only high-level disinfection between patients in the U.S. (24, 25, 26). As with flexible endoscopes, these devices may be difficult to clean or to do high-level disinfection/sterilization due to their intricate device design (e.g., long narrow lumina, hinges). Meticulous cleaning must precede any high-level disinfection/sterilization process. Although sterilization is preferred, there are no published outbreaks resulting following high-level disinfection of these scopes when properly cleaned and high-level disinfected. Newer models of these instruments can withstand steam sterilization that for critical items would be preferable to high-level disinfection. Semicritical items should be rinsed with sterile water after high-level disinfection to prevent their contamination with microorganisms that may be present in tap water, such as nontuberculous mycobacteria (10, 27, 28), Legionella (29, 30, 31), or gram-negative bacilli such as Pseudomonas (15, 17, 32, 33, 34). In circumstances where rinsing with sterile water rinse is not feasible, a tap water or filtered water (0.2Вm filter) rinse should be followed by an alcohol rinse and forced air drying (24, 34, 35). Forced-air drying markedly reduces bacterial contamination of stored endoscopes, most likely by removing the wet environment favorable for bacterial growth (35). After rinsing, items should be dried and stored (e.g., packaged) in a manner that protects them from recontamination. Some items that may come in contact with nonintact skin for a brief period of time (i.e., hydrotherapy tanks, bed side rails) are usually considered noncritical surfaces and are disinfected with intermediate-level disinfectants (e.g., phenolic, iodophor, alcohol, chlorine) (21). Since hydrotherapy tanks have been associated with spread of infection, some facilities have chosen to disinfect them with recommended levels of chlorine (21, 36). In the past it was recommended that mouthpieces and spirometry tubing be high-level disinfected (e.g., glutaraldehyde), but it was unnecessary to clean the interior surfaces of the spirometers (37). This was based on a study that showed that mouthpieces and spirometry tubing become contaminated with microorganisms, but there was no bacterial contamination of the surfaces inside the spirometers. More recently, filters have been used to prevent contamination of this equipment distal to the filter; such filters and the proximal mouthpiece should be changed between patients. Noncritical Items Noncritical items are those that come in contact with intact skin but not mucous membranes. Intact skin acts as an effective barrier to most microorganisms; therefore, the sterility of items coming in contact with intact skin is “not critical.” Examples of noncritical items are bedpans, blood pressure cuffs, crutches, bed rails, linens, some food utensils, bedside tables, patient furniture, and floors. In contrast to critical and some semicritical items, most noncritical reusable items may be decontaminated where they are used and do not need to be transported to a central processing area. There is virtually no risk of transmitting infectious agents to patients via noncritical items (33) when they are used as noncritical items and do not contact nonintact skin and/or mucous membranes. However, these items (e.g., bedside tables, bed rails) could potentially contribute to secondary transmission by contaminating hands of healthcare workers or by contact with medical equipment that will subsequently come in contact with patients (11, 38, 39, 40, 41, 42). Table 85.1 lists several low-level disinfectants that may be used for noncritical items. The exposure time listed in Table 85.1 is less than or equal to 10 minutes. Most Environmental Protection Agency (EPA)-registered disinfectants have a 10-minute label claim. However, multiple investigators have demonstrated the effectiveness of these disinfectants against vegetative bacteria [e.g., Listeria, Escherichia coli, Salmonella, vancomycin-resistant enterococci (VRE), methicillin-resistant Staphylococcus aureus (MRSA)], yeasts (e.g., Candida), mycobacteria (e.g., Mycobacterium tuberculosis), and viruses (e.g., poliovirus) at exposure time of 30 to 60 seconds (39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57). These products should be used in accordance with the manufacturers' recommendations (e.g., use-dilution, shelf-life, storage, material compatibility, safe use and disposal) but often are not; one study showed that only 14% of sampled disinfectants had the correct concentration (58). Mops and reusable cleaning cloths are regularly used to achieve low-level disinfection. However, they are commonly not kept adequately cleaned and disinfected, and if the water-disinfectant mixture is not changed regularly (e.g., after every three to four rooms, no longer than 60-minute intervals), the mopping procedure may actually spread heavy microbial contamination throughout the healthcare facility (59). In one study, standard laundering provided acceptable decontamination of heavily contaminated mop heads but chemical disinfection with a phenolic was less effective (59). The frequent laundering of mops (e.g., daily), therefore, is recommended. Changes in Disinfection and Sterilization Since 1981 The table contained in the CDC Guideline for Environmental Control prepared in 1981 as a guide to the appropriate selection and use of disinfectants has undergone several important changes (Table 85.1) (13). First, formaldehyde-alcohol has been deleted as a recommended chemical sterilant or high-level disinfectant, because it is irritating and toxic and not commonly used. Second, several new chemical sterilants have been added, including hydrogen peroxide, peracetic acid (51, 60, 61), and peracetic acid and hydrogen peroxide in combination. Third, 3% phenolics and iodophors have been deleted as high-level disinfectants because of their unproven efficacy against bacterial spores, M. tuberculosis, and/or some fungi (48, 62). Fourth, isopropyl alcohol and ethyl alcohol have been excluded as high-level disinfectants (13) because of their inability to inactivate bacterial spores and because of the inability of isopropyl alcohol to P.1477 inactivate hydrophilic viruses (e.g., poliovirus, Coxsackie virus) (63). Fifth, a 1:16 dilution of 2.0% glutaraldehyde–7.05% phenol–1.20% sodium phenate (which contained 0.125% glutaraldehyde, 0.440% phenol, and 0.075% sodium phenate when diluted) has been deleted as a high-level disinfectant, because this product was removed from the marketplace in December 1991 because of a lack of bactericidal activity in the presence of organic matter; a lack of fungicidal, tuberculocidal, and sporicidal activity; and reduced virucidal activity (43, 48, 49, 62, 64, 65, 66, 67, 68, 69, 70). Sixth, the exposure time required to achieve high-level disinfection has been changed from 10 to 30 minutes to 12 minutes or more depending on the scientific literature and the FDA-cleared label claim (23, 48, 60, 67, 71, 72, 73, 74, 75). Of note, one glutaraldehyde product has an FDA-cleared label claim of 5 minutes when used at 35ВC (76). Several new subjects have been added to the guideline: an expanded section on disinfection and sterilization of Creutzfeldt-Jakob disease (CJD) agent; inactivation of bioterrorists agents; decontamination of bone; surface disinfection; microbial contamination of disinfectants; air disinfection; and disinfection in the hemodialysis unit. DISINFECTION OF HEALTHCARE EQUIPMENT Concerns with Implementing the Spaulding Scheme One problem with implementing the Spaulding scheme is that of oversimplification. For example, it does not consider problems with reprocessing of complicated medical equipment that often is heat-sensitive or problems of inactivating certain types of infectious agents (e.g., prions such as CJD agent). Thus, in some situations it is still difficult to choose a method of disinfection, even after considering the categories of risk to patients. This is especially true for a few medical devices (e.g., arthroscopes, laparoscopes) in the critical category, because there is controversy about whether they should be sterilized or high-level disinfected (24, 77). Heat-stable scopes (e.g., many rigid scopes) should be steam sterilized. Some of these items cannot be steam sterilized, because they are heat-sensitive; further, sterilization by using ETO may be too time-consuming for routine use between patients (new technologies, such as hydrogen peroxide gas plasma and peracetic acid reprocessor, provide faster cycle times). However, evidence that sterilization of these items improves patient care by reducing the infection risk is lacking (25, 78, 79, 80, 81, 82). Many newer models of these instruments can withstand steam sterilization, which for critical items is the preferred method. Another problem with implementing the Spaulding scheme is how an instrument in the semicritical category (e.g., endoscopes) should be processed that would be used with a critical instrument that would have contact with sterile body tissues. For example, is an endoscope used for upper gastrointestinal tract investigation still a semicritical item when it is used with sterile biopsy forceps or when it is used in a patient who is bleeding heavily from esophageal varices? Provided that high-level disinfection is achieved, and all microorganisms with the exception of bacterial spores have been removed from the endoscope, then the device should not represent an infection risk and should remain in the semicritical category (83, 84, 85). There are no reports of infection with spore-forming bacteria from appropriately high-level disinfected endoscopes. An additional problem with the implementation of the Spaulding system is that the optimal contact time to achieve high-level disinfection has not been defined or varies among professional organizations, resulting in different strategies for disinfecting different types of semicritical items (e.g., endoscopes, applanation tonometers, endocavitary transducers, cryosurgical instruments, and diaphragm fitting rings). The impact of this variability is discussed below. Until simpler and effective alternatives are identified for device disinfection in clinical settings, it would be prudent to follow the recommendations in this chapter and in the guidelines of the CDC (17, 20, 86, 87, 88). Reprocessing of Endoscopes Physicians use endoscopes to diagnose and treat numerous medical disorders. Although endoscopes represent a valuable diagnostic and therapeutic tool in modern medicine and the incidence of infection associated with use has been reported as very low (about 1 in 1.8 million procedures) (89), more healthcare-associated outbreaks have been linked to contaminated endoscopes than to any other medical device (6, 7, 8). To prevent the spread of healthcare-associated infections, all heat-sensitive endoscopes (e.g., gastrointestinal endoscopes, bronchoscopes, nasopharyngoscopes) must be properly cleaned and at a minimum subjected to high-level disinfection following each use. High-level disinfection can be expected to destroy all microorganisms, although when high numbers of bacterial spores are present, a few spores may survive. Flexible endoscopes, by virtue of the types of body cavities they enter, acquire high levels of microbial contamination (bioburden) during each use (90). For example, the bioburden found on flexible gastrointestinal endoscopes following use has ranged from 105 to 1010 CFU/mL, with the highest levels being found in the suction channels (90, 91, 92, 93). The average load on bronchoscopes before cleaning was 6.4 Г— 104 CFU/mL. Cleaning reduces the level of microbial contamination by 4 to 6 log10 (74). Using HIV-contaminated endoscopes, several investigators have shown that cleaning completely eliminates the microbial contamination on the scopes (94, 95). Similarly, other investigators found that ETO sterilization or high-level disinfection (soaking in 2% glutaraldehyde for 20 minutes) were effective only when the device was first properly cleaned (96). High-level disinfectants cleared for marketing by the FDA include formulations with ≥2.4% glutaraldehyde, 0.55% OPA, 0.95% glutaraldehyde with 1.64% phenol/phenate, 7.35% hydrogen P.1478 peroxide with 0.23% peracetic acid, 1.0% hydrogen peroxide with 0.08% peracetic acid, and 7.5% hydrogen peroxide (76). Although all of these products have excellent antimicrobial activity, certain products based on oxidizing chemicals [e.g., 7.5% hydrogen peroxide and 1.0% hydrogen peroxide with 0.08% peracetic acid (the latter is no longer marketed)] have limited use, because they may cause cosmetic and functional damage to endoscopes (60). Two newer formulations (0.95% glutaraldehyde with 1.64% phenol/phenate, and 7.35% hydrogen peroxide with 0.23% peracetic acid) have been FDA-cleared but data regarding antimicrobial activity or materials compatibility have not yet been published in the scientific literature. ETO sterilization of flexible endoscopes is infrequent, because it requires a lengthy processing and aeration time (e.g., 12 hours) and is a potential hazard to staff and patients. The two products that are most commonly used for reprocessing endoscopes in the U.S. are glutaraldehyde and an automated, liquid chemical sterilization process that uses peracetic acid (97). The American Society of Gastrointestinal Endoscopy (ASGE) recommends glutaraldehyde solutions that do not contain surfactants, because the soapy residues of surfactants are difficult to remove during rinsing (2). OPA has begun to replace glutaraldehyde in many healthcare facilities as it possesses several potential advantages over glutaraldehyde: it causes no known irritation to the eyes and nasal passages, it does not require activation or exposure monitoring, and it has a 12-minute high-level disinfection claim in the U.S. (60). Disinfectants that are not FDA cleared and should not be used for reprocessing endoscopes include iodophors, chlorine solutions, alcohols, quaternary ammonium compounds, and phenolics. These solutions may still be in use outside the U.S., but their use should be strongly discouraged because of lack of proven efficacy against all microorganisms or materials incompatibility. The FDA cleared a package label for 2.4% glutaraldehyde that requires a 45-minute immersion at 25ВC to achieve high-level disinfection (i.e., 100% kill of M. tuberculosis). However, available data suggest that M. tuberculosis levels can be reduced by at least 8 log10 with cleaning (4 log10) (74, 92, 93, 98) followed by chemical disinfection for 20 minutes at 20ВC (4 to 6 log10) (74, 84, 99). Based on these data, the Association for Professionals in Infection Control (APIC) (100), the Society of Gastroenterology Nurses and Associates (SGNA) (34, 101) and ASGE (2) recommend that equipment be immersed in 2% glutaraldehyde at 20ВC for at least 20 minutes for high-level disinfection (2, 18, 50, 74, 85, 99, 102, 103, 104, 105, 106). In the absence of independently validated data regarding alternative exposure times of high-level disinfectants, the manufacturers' recommendations to achieve high-level disinfection should be followed. Currently, such data are available only for 2% glutaraldehyde solutions. Flexible endoscopes are particularly difficult to disinfect (107) and easy to damage because of their intricate design and delicate materials (108). Meticulous cleaning must precede any sterilization or high-level disinfection of these instruments. Failure to perform good cleaning may result in a sterilization or disinfection failure and outbreaks of infection may occur. Several studies have demonstrated the importance of cleaning in experimental studies with the duck HBV (96, 109), HIV (110), and Helicobacter pylori (111). Examining healthcare-associated infections related only to endoscopes through July 1992, Spach et al. (6) found that 281 infections were transmitted by gastrointestinal endoscopy and 96 were transmitted by bronchoscopy. The clinical spectrum ranged from asymptomatic colonization to death. Salmonella species and P. aeruginosa repeatedly were identified as causative agents of infections transmitted by gastrointestinal endoscopy, and M. tuberculosis (TB), atypical mycobacteria, and P. aeruginosa were the most common causes of infections transmitted by bronchoscopy. Major reasons for transmission were inadequate cleaning, improper selection of a disinfecting agent, failure to follow recommended cleaning and disinfection procedures (6, 8, 33), and flaws in endoscope design (112, 113) or automated endoscope reprocessors (7). Failure to follow established guidelines has continued to lead to infections associated with gastrointestinal endoscopes (8) and bronchoscopes (7). Potential device-associated problems should be reported to the FDA's Center for Devices and Radiologic Health. One multistate investigation found that 23.9% of the bacterial cultures from the internal channels of 71 gastrointestinal endoscopes grew ≥100,000 colonies of bacteria after completion of all disinfection/sterilization procedures and before use on the next patient (114). Automated endoscope reprocessors (AERs) offer several advantages compared to manual reprocessing: they automate and standardize several important reprocessing steps (115, 116, 117), reduce the likelihood that an essential reprocessing step will be skipped, and reduce personnel exposure to high-level disinfectants or chemical sterilants. Failure of AERs has been linked to outbreaks of infections (118) or colonization (7, 119), and the AER water filtration system may not be able to reliably provide bacteria-free rinse water (120, 121). It is critical that correct connectors between the AER and the device are established to ensure complete flow of disinfectants and rinse water (7, 122). In addition, some endoscopes such as the duodenoscopes [e.g., endoscopic retrograde cholangiopancreatography (ERCP)] contain features (e.g., elevator-wire channel) that require a flushing pressure that is not achieved by most AERs and must be reprocessed manually using a 2- to 5-mL syringe. New duodenoscopes equipped with a wider elevator-channel that AERs can reliably reprocess may be available in the future (117). Outbreaks involving removable endoscope parts (123, 124) such as suction valves and endoscopic accessories designed to be inserted through flexible endoscopes such as biopsy forceps emphasize the importance of cleaning to remove all foreign matter before high-level disinfection or sterilization (125). Some types of valves are now available as single-use, disposable products (e.g., bronchoscope valves) or steam sterilizable products (e.g., gastrointestinal endoscope valves). There is a need for further development and redesign of AERs (7, 126) and endoscopes (108, 127) so that they do not represent a potential source of infectious agents. Endoscopes employing disposable components (e.g., protective barrier devices or sheaths) can provide an alternative to conventional liquid chemical high-level disinfection/sterilization (128). Another new technology is a swallowable camera-in-a-capsule that travels through the digestive tract and transmits color pictures of the small intestine to a receiver that is worn outside the body. At present, this capsule will not replace colonoscopy. Recommendations for the cleaning and disinfection of endoscopic equipment have been published and should be strictly followed (2, 34, 100, 101, 129, 130, 131, 132). Unfortunately, audits have shown that personnel do not adhere to guidelines on reprocessing (133, 134, 135) and outbreaks of infection continue to occur (136, 137, 138). To ensure that reprocessing personnel are properly trained, there should be initial and annual competency testing for each individual who reprocesses endoscopic instruments (34, 139). P.1479 In general, endoscope disinfection or sterilization with a liquid chemical sterilant involves five steps after leak testing: (a) clean—mechanically clean internal and external surfaces, including brushing internal channels and flushing each internal channel with water and a detergent or enzymatic cleaners (leak testing is recommended for endoscopes before immersion); (b) disinfect—immerse endoscope in high-level disinfectant (or chemical sterilant) and perfuse (eliminates air pockets and ensures contact of the germicide with the internal channels) disinfectant into all accessible channels such as the suction/biopsy channel and air/water channel and expose for a time recommended for specific products; (c) rinse—rinse the endoscope and all channels with sterile water or filtered water (commonly used with AERs); if this is not feasible, use tap water; (d) dry—rinse the insertion tube and inner channels with alcohol and dry with forced air after disinfection and before storage; and (e) store the endoscope in a way that prevents recontamination and promotes drying (e.g., hung vertically). One study demonstrated that reprocessed endoscopes (e.g., air/water channel, suction/biopsy channel) were generally negative [100% after 24 hours; 90% after 7 days (1 CFU of coagulase-negative staphylococci in one channel)] for bacterial growth when stored by hanging in a vertical position in a ventilated cabinet (140). Because tap water may contain low levels of microorganisms, some have suggested that only sterile water, which may be prohibitively expensive (141), or AER filtered water be used. The suggestion to use only sterile water or filtered water is not consistent with published guidelines that allow tap water with an alcohol rinse and forced air-drying (2, 34, 100) or the scientific literature (35, 84). In addition, there has been no evidence of disease transmission when tap water followed by an alcohol rinse and forced air-drying has been used. AERs produce filtered water via passage through a bacterial filter (e.g., 0.2Вm). Filtered rinse water was identified as a source of bacterial contamination in a recent study that cultured the accessory and suction channels of endoscopes and the internal chambers of AERs between 1996 and 2001 and reported 8.7% of samples collected between 1996 and 1998 had bacterial growth with 54% being Pseudomonas species (142). Following the introduction of a system of hot water flushing of the piping (60ВC for 60 minutes daily), the frequency of positive cultures fell to approximately 2% with only rare isolation of >10 CFU/mL. In addition to these practices, a protocol should be developed that ensures that the user knows whether an endoscope has been appropriately cleaned and disinfected (e.g., using a room or cabinet for processed endoscopes only) or has not been reprocessed. Confusion can result when users leave endoscopes on movable carts, and it is unclear whether the endoscope has been processed or not. Although one guideline has recommended that an endoscope (e.g., a duodenoscope) should be reprocessed immediately before its use (131), other guidelines do not require this activity (2, 34), and with the exception of the Association of periOperative Registered Nurses (AORN), professional organizations do not recommend that reprocessing be repeated so long as the original processing is done correctly. As part of a quality assurance program, healthcare facility personnel may consider random bacterial surveillance cultures of processed endoscopes to ensure high-level disinfection or sterilization (7, 143, 144). Reprocessed endoscopes should be free of microbial pathogens except for small numbers of relatively avirulent microbes that represent exogenous environmental contamination (e.g., coagulase-negative staphylococci, Bacillus species, diphtheroids). It has also been suggested that the final rinse water used during endoscope reprocessing be microbiologically cultured at least monthly (145). The microbiologic standard that should be met has not been set. However, neither the routine culture of reprocessed endoscopes nor the final rinse water has been validated by correlating viable counts on an endoscope to infection following an endoscopic procedure. If culturing of reprocessed endoscopes were done, sampling the endoscope would assess water quality as well as other important steps (e.g., disinfectant effectiveness, exposure time, cleaning) in the reprocessing procedure. A number of methods for sampling endoscopes and water have been described (21, 140, 142, 144, 146, 147). The carrying case used to transport clean and reprocessed endoscopes outside of the healthcare environment should not be used to store an endoscope or to transport the instrument within the healthcare facility. A contaminated endoscope should never be placed in the carrying case as the case can also become contaminated. When the endoscope is removed from the case and properly reprocessed and put back in the case, the endoscope can become recontaminated by the case. If the carrying case becomes contaminated, it should be discarded (Olympus America, written communication, June 2002). Infection control professionals should ensure that institutional policies are consistent with national guidelines, and conduct infection control rounds periodically (e.g., at least annually) in areas where endoscopes are reprocessed to make certain there is compliance with policy. Breaches in policy should be documented and corrective action instituted. In incidents in which endoscopes were not exposed to a high-level disinfection process, all patients were assessed for possible acquisition of HIV, HBV, and hepatitis C virus (HCV). This highlights the importance of rigorous infection control (148, 149). Laparoscopes, Arthroscopes, and Cystoscopes Although high-level disinfection appears to be the minimum standard for processing laparoscopes, arthroscopes, and cystoscopes between patients (24, 77, 150, 151), there continues to be debate about this practice (80, 81, 152). However, neither side in the high-level disinfection versus sterilization debate has sufficient data on which to support its conclusions. Proponents of high-level disinfection refer to membership surveys (25) or institutional experiences (78) involving over 117,000 and 10,000 laparoscopic procedures, respectively, that cite a low risk of infection (<0.3%) when high-level disinfection is used for gynecologic laparoscopic equipment. Only one infection in the membership survey was linked to spores. In addition, studies conducted by Corson et al. (153, 154) demonstrated growth of common skin microorganisms (e.g., Staphylococcus epidermidis, diphtheroids) from the umbilical area even after skin preparation with povidone-iodine and ethyl alcohol. Similar microorganisms were recovered in some instances from the pelvic serosal surfaces P.1480 or from the laparoscopic telescopes, suggesting that the microorganisms probably were carried from the skin into the peritoneal cavity. Proponents of sterilization focus on the possibility of transmitting infection by spore-forming microorganisms. Researchers have proposed several reasons why sterility was not necessary for all laparoscopic equipment: only a limited number of microorganisms (usually в‰10) are introduced into the peritoneal cavity during laparoscopy; minimal damage is done to inner abdominal structures with little devitalized tissue; the peritoneal cavity tolerates small numbers of spore-forming bacteria; equipment is simple to clean and disinfect; surgical sterility is relative; the natural bioburden on rigid lumened devices is low (155); and no evidence that high-level disinfection, instead of sterilization, increases the infection risk (78, 80, 81). With the advent of laparoscopic cholecystectomy, there is justifiable concern with high-level disinfection as the degree of tissue damage and bacterial contamination is greater than with laparoscopic procedures in gynecology. Failure to completely dissemble, clean, and high-level disinfect the parts of a laparoscope has led to patient infections (156). Data from one study suggested that disassembly, cleaning, and proper assembly of laparoscopic equipment used in gynecologic procedures before steam sterilization presents no risk of infection (157). As with laparoscopes and other equipment that enter sterile body sites, arthroscopes ideally should be sterilized before used. Older studies demonstrated that these instruments were commonly (57%) only high-level disinfected in the U.S. (24, 77). A more recent survey, although with a response rate of only 5%, reported that high-level disinfection was used in 31% of the healthcare facilities and sterilization in the remainder (26). Presumably this is because the incidence of infection is low and the few infections are probably unrelated to the use of high-level disinfection rather than sterilization. In a retrospective study of 12,505 arthroscopic procedures, Johnston et al. (79) found an infection rate of 0.04% (five infections) when arthroscopes were soaked in 2% glutaraldehyde for 15 to 20 minutes. Four infections were caused by S. aureus, whereas the other was an anaerobic streptococcal infection. Since these microorganisms are very susceptible to high-level disinfectants such as 2% glutaraldehyde, the origin of these infections was likely the patient's skin. There are two case reports of Clostridium perfringens arthritis when the arthroscope was disinfected with glutaraldehyde for an exposure time that is not effective against spores (158, 159). Although only limited data are available, there is no evidence to demonstrate that high-level disinfection of arthroscopes, laparoscopes, or cystoscopes poses an infection risk to the patient. For example, a prospective study compared the reprocessing of arthroscopes and laparoscopes (per 1,000 procedures) with ETO sterilization to high-level disinfection with glutaraldehyde and found no statistically significant difference in infection risk between the two methods (i.e., ETO, 7.5/1,000 procedures; glutaraldehyde, 2.5/1,000 procedures) (80). The debate about high-level disinfection versus sterilization of laparoscopes and arthroscopes will go unsettled until there are published well-designed, randomized clinical trials. In the meantime, the recommendations of this chapter and the APIC and CDC guidelines should be followed (15, 17, 88). That is, laparoscopes, arthroscopes, cystoscopes, and other scopes that enter normally sterile tissue should be subjected to a sterilization procedure before each use; if this is not feasible, they should receive at least high-level disinfection. Tonometers, Diaphragm Fitting Rings, Cryosurgical Instruments, and Endocavitary Probes Disinfection strategies for other semicritical items (e.g., applanation tonometers, rectal/vaginal probes, cryosurgical instruments, and diaphragm fitting rings) are highly variable. For example, one study revealed that no uniform technique was in use for disinfection of applanation tonometers, with disinfectant contact times varying from <15 seconds to 20 minutes (24). In view of the potential for transmission of viruses [e.g., herpes simplex virus (HSV), adenovirus 8, or HIV] (160) by tonometer tips, the CDC recommends (86) that the tonometer tips be wiped clean and disinfected for 5 to 10 minutes with either 3% hydrogen peroxide, 5,000 parts per million (ppm) chlorine, 70% ethyl alcohol, or 70% isopropyl alcohol. Structural damage to SchiГёtz tonometers has been observed with a 1:10 sodium hypochlorite (5,000 ppm chlorine) and 3% hydrogen peroxide (161). After disinfection, the tonometer should be thoroughly rinsed in tap water and air dried before use. Although these disinfectants and exposure times should kill pathogens that can infect the eyes, there are no studies that provide direct support (162, 163). The guidelines of the American Academy of Ophthalmology for preventing infections in ophthalmology focus on only one potential pathogen, HIV (164). Because a short and simple decontamination procedure is desirable in the clinical setting, swabbing the tonometer tip with a 70% isopropyl alcohol wipe is sometimes practiced (163). Preliminary reports suggest that wiping the tonometer tip with an alcohol swab and then allowing the alcohol to evaporate may be an effective means of eliminating HSV, HIV, and adenovirus (163, 165, 166). However, since these studies involved only a few replicates and were conducted in a controlled laboratory setting, further studies are needed before this technique can be recommended. In addition, two reports have found that disinfection of pneumotonometer tips between uses with a 70% isopropyl alcohol wipe contributed to outbreaks of epidemic keratoconjunctivitis caused by adenovirus type 8 (167, 168). There are also limited studies that evaluated disinfection techniques for other items that contact mucous membranes, such as diaphragm fitting rings, cryosurgical probes, transesophageal echocardiography probes (169), or vaginal/rectal probes used in sonographic scanning. Lettau et al. (87) of the CDC supported the recommendation of a diaphragm-fitting ring manufacturer that involved using a soap-and-water wash followed by a 15-minute immersion in 70% alcohol. This disinfection method should be adequate to inactivate HIV, HBV, and HSV even though alcohols are not classified as high-level disinfectants, because their activity against picornaviruses is somewhat limited (63). There are no data on the inactivation of human papillomavirus by alcohol or other disinfectants, because in vitro replication of complete virions has not been achieved. Thus, although alcohol for 15 minutes should kill pathogens of relevance in P.1481 gynecology, there are no clinical studies that provide direct support for this practice. Vaginal probes are used in sonographic scanning. A vaginal probe and all endocavitary probes without a probe cover are semicritical devices as they have direct contact with mucous membranes (e.g., vagina, rectum, pharynx). Although one could argue that the use of the probe cover changes the category, this chapter proposes that a new condom/probe cover should be used to cover the probe for each patient, and since condoms/probe covers may fail (169, 170, 171, 172), high-level disinfection of the probe also should be performed. The relevance of this recommendation is reinforced with the findings that sterile transvaginal ultrasound probe covers have a very high rate of perforations even before use (0%, 25%, and 65% perforations from three suppliers) (172). After oocyte retrieval use, Hignett and Claman (172) found a very high rate of perforations in used endovaginal probe covers from two suppliers (75% and 81%), whereas Amis et al. (173) and Milki and Fisch (170) demonstrated a lower rate of perforations after use of condoms (0.9% and 2.0%, respectively). Rooks et al. (174) found that condoms were superior to commercially available probe covers for covering the ultrasound probe (1.7% for condoms versus 8.3% leakage for probe covers). These studies underscore the need for routine probe disinfection between examinations. Although most ultrasound manufacturers recommend the use of 2% glutaraldehyde for high-level disinfection of contaminated transvaginal transducers, the use of this agent has been questioned (175), because it may shorten the life of the transducer and may have toxic effects on the gametes and embryos (176). An alternative procedure for disinfecting the vaginal transducer has been offered by Garland and de Crespigny (177). It involves the mechanical removal of the gel from the transducer, cleaning the transducer in soap and water, wiping the transducer with 70% alcohol or soaking it for 2 minutes in 500 ppm chlorine, and rinsing with tap water and air drying. The effectiveness of this and other methods (173) has not been validated in either rigorous laboratory experiments or clinical use. High-level disinfection with a product that is not toxic to staff, patients, probes, and retrieved cells (e.g., hydrogen peroxide) should be used until such time as the effectiveness of alternative procedures against microbes of importance at the cavitary site is scientifically demonstrated. Other probes such as rectal, cryosurgical, and transesophageal probes/devices should also be subjected to high-level disinfection between patients. Ultrasound probes may also be used during surgical procedures and have contact with sterile body sites. These probes may be covered with a sterile sheath to reduce the level of contamination on the probe and reduce the risk of infection. However, since the sheath does not provide complete protection of the probe, the probes should be sterilized between each patient use as with other critical items. Some cryosurgical probes are not fully immersible. When reprocessing these probes, the tip of the probe should be immersed in a high-level disinfectant for the appropriate time (e.g., 20 minutes exposure with 2% glutaraldehyde) and any other portion of the probe that could have mucous membrane contact could be disinfected by immersion or wrapping with a cloth soaked in a high-level disinfectant to allow the recommended contact time. After disinfection, the probe should be rinsed with tap water and dried before use. Healthcare facilities that use nonimmersible probes should replace them as soon as possible with fully immersible probes. As with other high-level disinfection procedures, proper cleaning of probes is necessary to ensure the success of the subsequent disinfection (178). Muradali et al. (179) demonstrated a reduction of vegetative bacteria inoculated on vaginal ultrasound probes when the probes were cleaned with a towel. No information is available on either the level of contamination of such probes by potential viral pathogens such as HBV and human papilloma virus (HPV) or their removal by cleaning (such as with a towel). Because these pathogens may be present in vaginal and rectal secretions and contaminate probes during use, high-level disinfection of the probes after such use is recommended. Dental Instruments Scientific articles and increased publicity about the potential for transmitting infectious agents in dentistry have focused attention on dental instruments as possible agents for pathogen transmission (180, 181). The American Dental Association recommends that surgical and other instruments that normally penetrate soft tissue or bone (e.g., forceps, scalpels, bone chisels, scalers, and surgical burs) be classified as critical devices that should be sterilized after each use or discarded. The recommendations for dental instruments are somewhat unique in that instruments that are not intended to penetrate oral soft tissues or bone (e.g., amalgam condensers, and air/water syringes) but may come in contact with oral tissues are classified as semicritical but are recommended to be sterilized after each use (182). This is consistent with recommendations from CDC and FDA (183, 184). Handpieces that cannot be heat sterilized should be retrofitted to attain heat tolerance. Handpieces that cannot be retrofitted and thus are not able to be heat sterilized should not be used (184). Chemical disinfection is not recommended for critical or semicritical dental instruments. Methods of sterilization that may be used for critical or semicritical dental instruments and materials that are heat-stable include steam under pressure (autoclave), chemical (formaldehyde) vapor, and dry heat (e.g., 320ВF for 2 hours). The steam sterilizer is the method most commonly used by dental professionals (185). All three sterilization procedures can be damaging to some dental instruments, including steam-sterilized handpieces (186). Several studies have demonstrated variability among dental practices while trying to meet these recommendations (187, 188). For example, 68% of respondents believed they were sterilizing their instruments but did not use appropriate chemical sterilants or exposure times, and 49% of respondents did not challenge autoclaves with biologic indicators (187). Other investigators using biologic indicators have found a high portion (15–65%) of positive spore tests after assessing the efficacy of sterilizers used in dental offices. In one study of Minnesota dental offices, operator error, rather than mechanical malfunction (189), caused 87% of sterilization failures. Common factors in the improper use of sterilizers include chamber overload, low temperature setting, inadequate exposure time, failure to preheat the sterilizer, and interruption of the cycle. P.1482 Mail-return sterilization monitoring services use spore strips to test sterilizers in dental clinics, but delay caused by mailing to the test laboratory could potentially cause false-negative results. Studies revealed, however, that the poststerilization time and temperature after a 7-day delay had no influence on the test results (190). Miller and Sheldrake (191) also found that delays (7 days at 27ВC and 37ВC, 3-day mail delay) did not cause any predictable pattern of inaccurate spore tests (191). Uncovered operatory dental surfaces (e.g., countertops, chair switches, and light handles) should be disinfected between patients. This can be accomplished using products that are registered with the EPA as “hospital disinfectants.” There are several chemical classes (e.g., phenolics) that can be used for this purpose (182, 192, 193). If waterproof surface covers are used to reduce contamination of surfaces and are carefully removed and replaced between patients, the protected surfaces do not need to be disinfected between patients (unless visibly contaminated) but should be disinfected at the end of each working day. Decontamination of Bone Bone is the second most frequently transplanted tissue in humans, after blood (194). The risk of infections transmissible by allografts (e.g., bones, tendons, and ligaments) depends on the technique applied for procurement, preservation, and bacteriologic control, and on the prevalence of infectious carriers. HIV (195) and Clostridium sordelli (196) have been transmitted by bone transplantation. Despite the infection control measures employed to select the donors, the risk of infectious agents associated with the tissue obtained for transplantation cannot be ignored, and a safe, dependable method of secondary sterilization without damaging the tissue or recipient is essential. Two sterilization methods (gamma irradiation and ETO) that would inactivate spores have been associated with problems (e.g., weakened tissue, increased toxicity) that limit their use in processing of tissues for transplantation. Recently, a system to sterilize musculoskeletal tissues (e.g., bones, tendons) for use in bone grafting was developed using various chemical solutions to remove endogenous materials (e.g., blood, and bone marrow) and inactivate infectious agents. This vacuum-pressure cleaning system uses detergent, hydrogen peroxide, and alcohol in two cycles. Preliminary studies have shown it is effective in eliminating B. stearothermophilus spores (197). Although not often mentioned, instances have occurred in which a graft has been dropped on the operating room floor. To determine the amount of microbial contamination that occurs when the graft is dropped, surplus bone specimens from 50 procedures were dropped and submitted for culture. No positive cultures were obtained (198). Another study evaluated the most effective method for disinfecting contaminated human bone-tendon allografts (i.e., beef muscle, cadaveric human bone-tendon allografts, and Achilles tendon-calcaneus allografts) (199). A 2% and 4% chlorhexidine irrigation solution and 4% chlorhexidine/triple antibiotic bath completely disinfected the test tissues after an exposure time of 10 to 12 minutes. Disinfection of HBV-, HCV-, HIV- or Tuberculosis-Contaminated Devices Should we sterilize or high-level disinfect semicritical medical devices contaminated with blood from patients infected with HBV, HCV, or HIV or with respiratory secretions from patients with pulmonary tuberculosis? The CDC recommendation for high-level disinfection is appropriate, because experiments have demonstrated the effectiveness of high-level disinfectants to inactivate these and other pathogens that may contaminate semicritical devices (54, 55, 64, 72, 95, 106, 110, 200, 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212, 213, 214, 215). Nonetheless, some healthcare facilities have modified their disinfection procedures when endoscopes are used with a patient known or suspected to be infected with HBV, HIV, or M. tuberculosis (24, 216). This is inconsistent with the concept of standard precautions that presumes that all patients are potentially infected with bloodborne pathogens (207). Several studies have highlighted the inability to distinguish HBV- or HIV-infected patients from noninfected patients on clinical grounds (217, 218, 219). It also is likely that mycobacterial infection will not be clinically apparent in many patients. In most instances, hospitals that altered their disinfection procedure used ETO sterilization on the endoscopic instruments, because they believed this practice reduced the risk of infection (24, 216). ETO is not routinely used for endoscope sterilization because of the lengthy processing time. Endoscopes and other semicritical devices should be managed the same way whether or not the patient is known to be infected with HBV, HCV, HIV, or M. tuberculosis. An evaluation of a manual disinfection procedure to eliminate HCV from experimentally contaminated endoscopes provided some evidence that cleaning and 2% glutaraldehyde for 20 minutes should prevent transmission (215). Using experimentally contaminated hysteroscopes, Sartor etal. (105) detected HCV by polymerase chain reaction (PCR) in one (3%) of 34 samples following cleaning with a detergent, but no samples were positive following treatment with a 2% glutaraldehyde solution for 20 minutes. Rey et al. (103) demonstrated complete elimination of HCV (as detected by PCR) from endoscopes used on chronically infected patients following cleaning and disinfection for 3 to 5 minutes in glutaraldehyde. Similarly, Chanzy et al. (215) used PCR to demonstrate complete elimination of HCV following standard disinfection of experimentally contaminated endoscopes. The inhibitory activity of a phenolic and a chlorine compound on HCV showed that the phenolic inhibited the binding and replication of HCV but the chlorine was ineffective, probably due to its low concentration and its neutralization in the presence of organic matter (220). Disinfection in the Hemodialysis Unit Hemodialysis systems include hemodialysis machines, water supply, water treatment systems, and the distribution system. During hemodialysis, patients have acquired bloodborne viruses and pathogenic bacteria (221, 222, 223). Cleaning and disinfection are important components of infection control in a hemodialysis center. Disinfectants used to reprocess hemodialyzers, hemodialysis machines, and water treatments systems are now regulated P.1483 by the FDA as a class II medical device, subject to 510[k] clearance. Disinfection on noncritical surfaces (e.g., dialysis bed or chair, countertops, external surfaces of dialysis machines, and equipment—scissors, hemostats, clamps, blood pressure cuffs, stethoscopes) should be done with low-level disinfectants unless the item is visibly contaminated with blood, in which case a tuberculocidal agent (or a disinfectant with specific label claims for HBV and HIV) should be used (222, 224). This procedure accomplishes two goals: it removes soil on a regular basis, and maintains an environment that is consistent with good patient care. Disinfection of hemodialyzers is accomplished with peracetic acid, formaldehyde, glutaraldehyde, heat and citric acid, and chlorine-containing compounds. Disinfection of hemodialysis systems is normally accomplished by chlorine-based disinfectants (e.g., sodium hypochlorite), aqueous formaldehyde, heat pasteurization, ozone, or peracetic acid. All products must be used according to the manufacturers' recommendations. Some dialysis systems use hot-water disinfection for the control of microbial contamination. Since about 80% of U.S. chronic hemodialysis centers reprocess (i.e., reuse) dialyzers for the same patient, high-level disinfection is also common in dialysis centers. Three disinfectants were commonly used in a 2000 survey: a peracetic acid formulation was used by 59% of centers that reused dialyzers, formaldehyde by 31%, and glutaraldehyde by 5%. A heat process (221, 222, 225) was used by 4%. Detailed infection control recommendations, to include disinfection and sterilization and the use of dedicated machines for hepatitis B surface antigen (HBsAg)-positive patients, in the hemodialysis setting may be found in two reviews (221, 222). Inactivation of Clostridium difficile The source of healthcare-associated acquisition of C. difficile in nonepidemic settings has not been determined. The environment and carriage on the hands of healthcare personnel have been considered as possible sources of infection. Carpeted rooms occupied by a patient with C. difficile are more heavily contaminated with C. difficile than noncarpeted rooms (226). Since C. difficile may display increased levels of spore production when exposed to non–chlorine-based cleaning agents and the spores are more resistant than vegetative cells to commonly used surface disinfectants (227), some investigators have recommended the use of dilute solutions of hypochlorite (1,600 ppm available chlorine) for routine environmental disinfection of rooms of patients with C. difficile–associated diarrhea or colitis (228) or in units with high C. difficile rates (229). Mayfield et al. (229) showed a marked reduction in C. difficile–associated diarrhea rates in the bone marrow transplant unit (from 8.6 to 3.3 cases per 1,000 patient-days) during the period of bleach disinfection (1:10 dilution) of environmental surfaces compared to cleaning with a quaternary ammonium compound. Thus, use of a diluted hypochlorite should be considered in units with high C. difficile rates. However, studies have shown that asymptomatic patients constitute an important reservoir within the healthcare facility and that person-to-person transmission is the principal means of transmission between patients. Thus, handwashing, barrier precautions, and meticulous environmental cleaning with a low-level disinfectant (e.g., germicidal detergent) should be effective in preventing the spread of the microorganism (230). Contaminated medical devices such as colonoscopes could serve as vehicles for the transmission of C. difficile spores. For this reason, investigators have studied commonly used disinfectants and exposure times to assess whether current practices may be placing patients at risk. Data demonstrate that 2% glutaraldehyde reliably kills C. difficile spores using exposure times of 5 to 20 minutes (70, 231, 232). Inactivation of Creutzfeldt-Jakob Disease Agent Creutzfeldt-Jakob disease (CJD) is a degenerative neurologic disorder of humans with an incidence in the U.S. of approximately 1 case/million population/year (233, 234). CJD is thought to be caused by a proteinaceous infectious agent or prion. CJD is related to other human transmissible spongiform encephalopathies (TSEs) that include kuru (zero incidence, now eradicated), Gertsmann-StrГussler-Scheinker (GSS) syndrome (1/billion), and fatal familial insomnia syndrome (FFI) (<1/billion). Prion diseases do not elicit an immune response, result in a noninflammatory pathologic process confined to the central nervous system, have an incubation period of years, and usually are fatal within 1 year of diagnosis. Recently, a new variant form of CJD (vCJD) has been recognized that is acquired from cattle with bovine spongiform encephalopathy (BSE, or “mad-cow” disease). As of November 4, 2002, a total of 138 vCJD cases have been reported worldwide, 128 in the United Kingdom, six in France, and one each in Italy, Ireland, Canada, and the U.S. (235). Each of the latter three cases had resided in the U.K. during the U.K. outbreak of BSE (L Schonberger, written communication, 2002). Compared with CJD patients, vCJD patients are younger (29 vs. 65 years of age), have a longer duration of illness (14 vs. 4.5 months), and present with sensory and psychiatric symptoms that are uncommon with CJD. The agents of CJD and other TSEs exhibit an unusual resistance to conventional chemical and physical decontamination methods. Since the CJD agent is not readily inactivated by conventional disinfection and sterilization procedures and because of the invariably fatal outcome of CJD, the procedures for disinfection and sterilization of the CJD prion have been both cautious and controversial for many years. CJD occurs as both a sporadic and familial disease. Less than 1% of CJD episodes have resulted from healthcare-associated transmission; the majority result from use of contaminated tissues or grafts. Iatrogenic CJD has been described in humans in three circumstances: after use of contaminated medical equipment on patients undergoing invasive procedures (two confirmed cases); after patients received extracted pituitary hormones (>130 cases); and after patients received an implant of contaminated grafts from humans (cornea, three cases; dura mater, >110 cases) (236, 237). All known instances of iatrogenic CJD have resulted from exposure to infectious brain, pituitary, or eye tissue. Tissue infectivity studies in experimental animals have determined the infectiousness of different body tissues (Table 85.3) (238, 239). P.1484 Transmission via stereotactic electrodes is the only convincing example of transmission via a medical device. The electrodes had been implanted in a patient with known CJD and then cleaned with benzene and “sterilized” with 70% alcohol and formaldehyde vapor. Two years later, these electrodes were retrieved and implanted into a chimpanzee in which the disease developed (240). The method used to sterilize these electrodes would not currently be considered an adequate method for sterilizing medical devices. The infrequent transmission of CJD via contaminated medical devices probably reflects the inefficiency of transmission unless dealing with neural tissue and the effectiveness of conventional cleaning and current disinfection and sterilization procedures (241). Retrospective studies suggest four other episodes may have resulted from use of contaminated instruments in neurosurgical operations (242, 243). An index CJD case was identified in one case and in this case the surgical instruments were cleaned with soap and water followed by exposure to dry heat for an unspecified time and temperature (243). All six cases of CJD associated with neurosurgical instruments occurred in Europe between 1953 and 1976 and details of the reprocessing methods for the instruments are incomplete (L. M. Sehulster, written communication, 2000). There are no known episodes of CJD attributable to the reuse of devices contaminated with blood or via transfusion of blood products. The risk of occupational transmission of CJD to a healthcare worker is remote. Healthcare workers should use standard precautions when caring for patients with CJD. TABLE 85.3. COMPARATIVE FREQUENCY OF INFECTIVITY IN ORGANS/TISSUE/BODY FLUIDS OF HUMANS WITH TRANSMISSIBLE SPONGIFORM ENCEPHALOPATHIES Infectious Risks1 Tissue High Low Brain (including dura mater), spinal cord, eyes Cerebrospinal fluid, liver, lymph node, kidney, lung, spleen, placenta None Peripheral nerve, intestine, bone marrow, whole blood, leukocytes, serum, thyroid gland, adrenal gland, heart, skeletal muscle, adipose tissue, gingiva, prostate, testis, tears, nasal mucus, saliva, sputum, urine, feces, semen, vaginal secretions, milk Modified from 236, 241, 706. 1 Infectious risks: high = transmission to inoculated animals > 50%; low = transmission to inoculated animals ≥ 10–20% (except for lung tissue, for which transmission is 50%); none = transmission to inoculated animals 0% (several tissues in this category had few tested specimens). To minimize the possibility of use of neurosurgical instruments that have been potentially contaminated during procedures performed on patients in whom CJD is later diagnosed, healthcare facilities should consider using the sterilization guidelines outlined below for neurosurgical instruments used during brain biopsy done on patients in whom a specific lesion has not been demonstrated (e.g., by magnetic resonance imaging or computed tomography scans). Alternatively, neurosurgical instruments used in such patients could be disposable (241) or instruments quarantined until the pathology of the brain biopsy is reviewed and CJD excluded. The inactivation of prions by disinfectant and sterilization processes has been studied by several investigators, but these studies do not reflect the reprocessing procedures in a clinical setting. First, these studies have not incorporated a cleaning procedure that normally reduces microbial contamination by 4 log10 (15) and reduces protein contamination (244, 245, 246). Second, the prion studies have been done with tissue homogenates, and the protective effect of tissue may explain, in part, why the CJD agent is difficult to inactivate (247). Brain homogenates have been shown to confer thermal stability to small subpopulations of the scrapie agent and some viruses. Third, results of inactivation studies of prions have been inconsistent due to the use of differing methodologies, which may have varied by prion strain, prion concentration, test tissue (intact brain tissue, brain homogenates, partially purified preparations), test animals, duration of follow-up of inoculated animals, exposure container, method of calculating log-reductions in infectivity, concentration of the disinfectant at the beginning and end of an experiment, cycle parameters of the sterilizer, and exposure conditions. Despite these limitations, there is some consistency in the results (241, 248). To provide scientifically based recommendations, research in which actual medical instruments are contaminated with prions (including vCJD) followed by cleaning and either conventional sterilization or disinfection, or special prion reprocessing, should be undertaken. Based on the disinfection studies many, but not all, disinfection processes fail to inactivate clinically significant numbers of prions (Table 85.4) (249, 250, 251, 252, 253, 254, 255, 256, 257, 258, 259, 260, 261, 262, 263). There are four chemicals that reduce the prion titer by >3 log10 in 1 hour: chlorine, a phenolic (based on ortho-phenylphenol, p-tertiary-amylphenol and ortho-benzyl-para-chlorophenol) at >0.9%, guanidine thiocyanante, and sodium hydroxide. Of these four chemical compounds, chlorine has provided the most consistent prion inactivation P.1485 results (241). However, the corrosive nature of chlorine makes it unsuitable for semicritical devices such as endoscopes. TABLE 85.4. EFFICACY OF CHEMICAL DISINFECTANTS IN INACTIVATING PRIONS Ineffective chemical disinfectants (в‰3-log10 reduction in 1 hour) Effective chemical disinfectants (>3-log10 reduction in 1 hour) Alcohol 50% Ammonia 1.0M Chlorine dioxide 50 ppm Formaldehyde 3.7% Glutaraldehyde 5% Hydrochloric acid 1.0 N Hydrogen peroxide 3% Iodine 2% Peracetic acid Phenol/phenolics 0.6% Potassium permanganate 0.1–0.8% Sodium deoxycholate 5% Sodium dodecyl sulfate 0.5–5% Tego (dodecyl-di[aminoethyl]-glycine) 5% Triton X-100 1% Urea 4–8 M Chlorine >1,000 ppm Guanidine thiocyanate Guanidine thiocyanate A phenolic disinfectant (see CJD text) >0.9% Modified from 241, 707. Prions also exhibit an unusual resistance to conventional physical decontamination methods (Table 85.5). Although there is some disagreement on the ideal time and temperature cycle for autoclaving, the recommendation for 134ВC for ≥18 minutes (prevacuum) and 132ВC for 60 minutes (gravity displacement) are based on the scientific literature (251, 252, 253, 255, 259, 262, 264, 265). Some investigators also have found that combining sodium hydroxide (e.g., 0.09 N for 2 hours) with steam sterilization for 1 hour at 121ВC results in complete loss of infectivity (255, 265). However, the combination of sodium hydroxide and steam sterilization may be deleterious to surgical instruments (248), sterilizers, as well as sterilizer operators who could be breathing vaporized chemicals unless engineering controls or use of personal protective equipment (PPE) prevents exposure. TABLE 85.5. EFFICACY OF STERILIZATION PROCESSES IN INACTIVATING PRIONS The disinfection and sterilization recommendations for CJD in this chapter are based on the belief that infection control measures should be predicated on epidemiologic evidence linking specific body tissues or fluids to transmission of CJD, infectivity assays demonstrating that body tissues or fluids are contaminated with infectious prions, cleaning data using biologic indicators and proteins (74, 244, 245), inactivation data of prions, the risk of disease transmission with the use of the instrument or device, and a review of other recommendations (11, 266, 267; L. M. Sehulster, written communication, 2000). Other CJD recommendations have been based primarily on inactivation studies (15, 248, 268). Thus, the three parameters integrated into disinfection and sterilization processing are the risk of the patient's having a prion disease, the comparative infectivity of different body tissues, and the intended use of the medical device (11, 266, 267; L. M. Sehulster, written communication, 2000). High-risk patients include those with known prion disease; rapidly progressive dementia consistent with possible prion disease; familial history of CJD, GSS, FFI; patients known to carry a mutation in the PrP gene involved in familial TSEs; a history of dura mater transplants; or a known history of cadaver-derived pituitary hormone injection. High-risk tissues include brain, spinal cord, and eye. All other tissues are considered low or no risk (Table 85.3). Critical devices are defined as devices that enter sterile tissue or the vascular system (e.g., implants). Semicritical devices are defined as devices that contact nonintact skin or mucous membranes (e.g., endoscopes). The AORN recommended practices for reprocessing surgical instruments exposed to CJD are consistent with the following recommendations (241, 269). Recommendations for disinfection and sterilization of prion-contaminated medical devices are as follows. For high-risk tissues, high-risk patients, and critical or semicritical medical devices, clean the device and sterilize preferably using a combination of sodium hydroxide and autoclaving as recommended by the World Health Organization (WHO) (236) [e.g., immerse in 1 N NaOH (1 N NaOH is a solution of 40 g NaOH in 1 L of water) for 1 hour; remove and rinse in water, then transfer to an open pan and autoclave (121ВC gravity displacement or 134ВC porous or prevacuum sterilizer) for 1 hour; or immerse instruments in 1 N NaOH for 1 hour and heat in a gravity displacement sterilizer at 121ВC for 30 minutes; clean; and subject to routine sterilization], or by autoclaving at 134ВC for 18 minutes in a prevacuum sterilizer, or 132ВC for 1 hour in a gravity displacement sterilizer. The temperature should not exceed 134ВC since under certain conditions the effectiveness of autoclaving actually declines as the temperature is increased (e.g., 136ВC, 138ВC) (264). The combined use of autoclaving in sodium hydroxide has raised concerns of possible damage to autoclaves (T. K. Moore, written communication, October 2002), and hazards to operators due to the caustic vapors. This risk can be minimized by the use of polypropylene containment pans and lids designed for condensation to collect and drip back into the pan (270). Hot NaOH is more caustic than NaOH at room temperature, so even greater care should be taken to avoid exposure to it when hot (D. Asher, written communication, November 2002). Instruments should be kept wet or damp until they are decontaminated and they should be decontaminated as soon as possible after use. Dried films of tissue are more resistant to prion inactivation by steam sterilization compared to tissues that were kept moist. This may relate to the rapid heating that occurs in the film of dried material compared to the bulk of the sample, and the rapid fixation of the prion protein in the dried film (259). It also appears that prions in the dried portions of the brain macerates are less efficiently inactivated than undisturbed tissue. Prion-contaminated medical devices that are impossible or difficult to clean should be discarded. Flash sterilization should not be used for reprocessing. To minimize environmental contamination, noncritical environmental surfaces should be covered with plastic-backed paper and when contaminated with high-risk tissues the paper should be properly discarded. Environmental surfaces (noncritical) contaminated with high-risk tissues (e.g., laboratory surfaces) should be cleaned and then spot decontaminated with a 1:10 dilution of hypochlorite solutions. For added safety, one could consider reprocessing critical or semicritical devices contaminated with low-risk tissues from high-risk patients with special prion reprocessing. Although low risk tissue has been found to transmit CJD at a low frequency (Table 85.3), this has been demonstrated only when low-risk tissue is inoculated into the brain of a susceptible animal. However, in humans, medical instruments contaminated with low-risk tissue would be unlikely to transmit infection following P.1486 conventional cleaning and sterilization since the instruments would not be used in the central nervous system. Environmental surfaces contaminated with low-risk tissues require only standard (i.e., blood-contaminated) disinfection (11, 241, 266). Since noncritical surfaces are not involved in disease transmission, the normal exposure time (в‰10 minutes) is recommended. Most of the data that form the basis of these recommendations have been generated from studies of the prions responsible for sporadic CJD or animal TSE diseases (e.g., scrapie). Limited data are available on which to base recommendations for the prevention of vCJD. To date, there have been no reports of human-to-human transmission of vCJD by blood or tissue. Unlike sporadic CJD, patients with vCJD have prions detectable in the lymphoid tissue. Furthermore, prion proteins may be detectable before the onset of clinical illness. This has raised concern about the possible human-to-human transmission of vCJD by medical instruments contaminated with such tissues. On the basis of these concerns, the use of prion disinfection and sterilization guidelines (or single-use instruments) has been proposed in the U.K. for instruments used in dental procedures (271), eye procedures (272), or tonsillar surgery (273) on patients at high risk of sporadic CJD or vCJD. Following complications (death in one patient and increased bleeding) associated with the use of single-use instruments in tonsillar surgery, it is now advised in the U.K. that given the balance of risk, surgeons can return to using reusable surgical equipment. If epidemiologic and infectivity data show that these tissues represent a transmission risk, then CJD sterilization precautions (or use of disposable equipment) could be extended to equipment used for these procedures (274). In addition, chronic wasting disease in deer and elk have been spreading in the midwestern U.S. Transmission of chronic wasting disease to humans has not been described. OSHA Bloodborne Pathogen Standard In December 1991, the Occupational Safety and Health Administration (OSHA) promulgated a standard entitled “Occupational Exposure to Bloodborne Pathogens” to eliminate or minimize occupational exposure to bloodborne pathogens (275). One component of this requirement is that all equipment and environmental and working surfaces be cleaned and decontaminated with an appropriate disinfectant after contact with blood or other potentially infectious materials. Although the OSHA standard does not specify the type of disinfectant or procedure, the OSHA compliance document (276) suggests that a germicide must be tuberculocidal to kill the HBV. Thus, it suggests that a tuberculocidal agent should be used to clean blood spills on noncritical surfaces. To follow the OSHA compliance document, a tuberculocidal disinfectant (e.g., phenolic, chlorine) would be needed to clean a blood spill. This caused concern among housekeeping managers who tried to identify disinfectant detergents claiming to be tuberculocidal on the assumption that such products would be effective in eliminating transmission of HBV. This directive could be problematic on a practical level for three reasons. First, nontuberculocidal disinfectants such as quaternary ammonium compounds inactivate the HBV (208). Second, noncritical surfaces are rarely, if ever, involved in disease transmission (33). Third, the exposure times that manufacturers use to achieve their label claims are not employed in healthcare settings to disinfect noncritical surfaces. For example, to make a label claim against HBV, HIV, or M. tuberculosis, a manufacturer must demonstrate inactivation of these microorganisms when exposed to a disinfectant for 10 minutes. This cannot be practically achieved for disinfection of environmental surfaces in a healthcare setting. The EPA will allow a label of a shorter exposure time when supported by test data. Multiple scientific papers have demonstrated significant microbial reduction with exposure times of less than 10 minutes (39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 51, 52, 53, 54, 55, 56, 57). For this reason and since exposure times of 10 minutes or greater are not feasible for disinfection of environmental surfaces in healthcare settings, most healthcare facilities apply the disinfectant and allow it to dry (~1 minute). However, contact times should be at least 30 seconds to achieve significant microbial inactivation. In February 1997, OSHA amended its policy and stated that EPA-registered disinfectants that are labeled as effective against HIV and HBV would be considered as appropriate disinfectants “provided such surfaces have not become contaminated with agent(s) or volumes of or concentrations of agent(s) for which higher level disinfection is recommended.” When bloodborne pathogens other than HBV or HIV are of concern, OSHA continues to require the use of EPA-registered tuberculocidal disinfectants or hypochlorite solution (diluted 1:10 or 1:100 with water) (207, 277). Recent studies demonstrate that, in the presence of large blood spills, a 1:10 final dilution of hypochlorite solution should be initially used to inactivate bloodborne viruses (56, 214) to minimize risk of disease to the healthcare worker from percutaneous injury during the cleanup process. Emerging Pathogens (Cryptosporidium, H. pylori, E. coli O157:H7, Rotavirus, Human Papilloma Virus, Norwalk Virus) Emerging pathogens are of growing concern to the general public and infection control professionals. Relevant pathogens include Cryptosporidium parvum, H. pylori, E. coli O157:H7, HIV, HCV, rotavirus, multidrug-resistant M. tuberculosis, and nontuberculosis mycobacteria (e.g., M. chelonae). The susceptibility of each of these pathogens to chemical disinfectants/sterilants has been studied. With the exceptions discussed below, all of these emerging pathogens are susceptible to currently available chemical disinfectants/sterilants (278). Cryptosporidium is resistant to chlorine at concentrations used in potable water. C. parvum is not completely inactivated by most disinfectants used in healthcare including ethyl alcohol (279), glutaraldehyde (279, 280), 5.25% hypochlorite (279), peracetic acid (279), OPA (279), phenol (279, 280), povidone-iodine (279, 280), and quaternary ammonium compounds (279). The only chemical disinfectants/sterilants able to inactivate greater than 3 log10 of C. P.1487 parvum were 6% and 7.5% hydrogen peroxide (279). Sterilization methods will fully inactivate C. parvum, including steam (279), ethylene oxide (279, 281), and hydrogen peroxide gas plasma (279). Although most disinfectants are ineffective against C. parvum, current cleaning and disinfection practices appear satisfactory to prevent healthcare-associated transmission. For example, endoscopes are unlikely to represent an important vehicle for the transmission of C. parvum because the results of bacterial studies indicate mechanical cleaning will remove approximately 104 microorganisms and drying rapidly results in loss of C. parvum viability (e.g., 30 minutes, 2.9 log10 decrease, and 60 minutes, 3.8 log10 decrease) (279). Chlorine at ~1 ppm has been found capable of eliminating approximately 4 log10 of E. coli O157:H7 within 1 minute in a suspension test (57). Electrolyzed oxidizing water at 23ВC was effective in 10 minutes in producing a 5-log10 decrease in E. coli O157:H7 inoculated onto kitchen cutting boards (282). The following disinfectants eliminated >5 log10 of E. coli O157:H7 within 30 seconds: a quaternary ammonium compound, a phenolic, a hypochlorite (1:10 dilution of 5.25% bleach), and ethanol (46). Disinfectants including chlorine compounds are able to reduce E. coli O157:H7 experimentally inoculated onto alfalfa seeds or sprouts (283, 284) or beef carcass surfaces (285). Only limited data are available on the susceptibility of H. pylori to disinfectants. Using a suspension test, Akamatsu et al. (53) assessed the effectiveness of a variety of disinfectants against nine strains of H. pylori. Ethanol (80%) and glutaraldehyde (0.5%) killed all strains within 15 seconds; chlorhexidine gluconate (0.05%, 1.0%), benzalkonium chloride (0.025%, 0.1%), alkyldiaminoethylglycine hydrochloride (0.1%), povidone-iodine (0.1%), and sodium hypochlorite (150 ppm) killed all strains within 30 seconds. Both ethanol (80%) and glutaraldehyde (0.5%) retained similar bactericidal activity in the presence of organic matter, whereas the other disinfectants showed reduced bactericidal activity. In particular, the bactericidal activity of povidone-iodine (0.1%) and sodium hypochlorite (150 ppm) was markedly decreased in the presence of dried yeast solution with killing times increased to 5 to 10 minutes and 5 to 30 minutes, respectively. Immersion of biopsy forceps in formalin before obtaining a specimen does not affect the ability to culture H. pylori from the biopsy specimen (286). The following methods have been demonstrated to be ineffective for eliminating H. pylori from endoscopes: cleaning with soap and water (104, 287), immersion in 70% ethanol for 3 minutes (288), instillation of 70% ethanol (111), instillation of 30 mL of 83% methanol (287), and instillation of 0.2% Hyamine solution (289). The differing results with regard to the efficacy of ethyl alcohol are unexplained. Cleaning followed by use of 2% alkaline glutaraldehyde (or automated peracetic acid) has been demonstrated by culture to be effective in eliminating H. pylori (104, 287, 290). Epidemiologic investigations of patients who had undergone endoscopy with endoscopes mechanically washed and disinfected with 2.0% to 2.3% glutaraldehyde have revealed no evidence of person-to-person transmission of H. pylori (111, 291). Disinfection of experimentally contaminated endoscopes using 2% glutaraldehyde (10-, 20-, and 45-minute exposure times) or the peracetic acid system (with and without active peracetic acid) has been demonstrated to be effective in eliminating H. pylori (104). H. pylori DNA has been detected by PCR in fluid flushed from endoscope channels following cleaning and disinfection with 2% glutaraldehyde (292). The clinical significance of this finding is unclear. In vitro experiments have demonstrated a >3.5-log10 reduction in H. pylori after exposure to 0.5 mg/L of free chlorine for 80 seconds (293). An outbreak of healthcare-associated rotavirus gastroenteritis on a pediatric unit has been reported (294). Person-to-person transmission via the hands of healthcare workers was the proposed mechanism. Prolonged survival of rotavirus on environmental surfaces (90 minutes to more than 10 days at room temperature) and hands (>4 hours) has been demonstrated. Rotavirus suspended in feces can survive for a longer period of time (295, 296). Vectors for this infection have included air, hands, fomites, water, and food (296). Products with demonstrated efficacy (>3 log10 reduction in virus) against rotavirus within 1 minute include 95% ethanol, 70% isopropanol, some phenolics, 2% glutaraldehyde, 0.35% peracetic acid, and some quaternary ammonium compounds (52, 297, 298, 299). In a human challenge study, a disinfectant spray (0.1% ortho-phenylphenol and 79% ethanol), sodium hypochlorite (800 ppm free chlorine), and a phenol-based product (14.7% phenol diluted 1:256 in tap water) when sprayed onto contaminated stainless steel disks, were effective in interrupting the transfer of a human rotavirus from stainless steel disk to fingerpads of volunteers after an exposure time of 3 to 10 minutes. A quaternary ammonium product (7.05% quaternary ammonium compound diluted 1:128 in tap water) and tap water allowed transfer of virus (45). There are no data on the inactivation of human papillomavirus by alcohol or other disinfectants because in vitro replication of complete virions has not been achieved. Similarly, little is known about the inactivation of Norwalk virus and Norwalk virus–like particles (members of the family Caliciviridae and important causes of gastroenteritis in humans), as they cannot be grown in tissue culture. Inactivation studies with a closely related cultivable virus (i.e., feline calicivirus) have shown the effectiveness of chlorine, glutaraldehyde, and iodine-based products, whereas the quaternary ammonium compound, detergent, and ethanol failed to inactivate the virus completely (300). Inactivation of Bioterrorism Agents Regarding the potential for biologic terrorism (301, 302), the CDC has categorized several agents as “high priority” because they can be easily disseminated or transmitted person to person, cause high mortality, and are likely to cause public panic and social disruption (303). These agents include Bacillus anthracis (anthrax), Yersinia pestis (plague), variola major (smallpox), Clostridium botulinum toxin (botulism), Francisella tularensis (tularemia), filoviruses (Ebola hemorrhagic fever, Marburg hemorrhagic fever); and arenaviruses [Lassa (Lassa fever), Junin (Argentine hemorrhagic fever)], and related viruses (303). Sterilization and disinfection have a role regarding the potential agents of bioterrorism. First, the susceptibility of these agents to germicides in vitro is similar to other related pathogens. For example, variola is similar to vaccinia (63) and B. anthracis is similar to B. atrophaeus (formerly B. subtilis) (304). Thus, one can extrapolate from the larger database available on the susceptibility of genetically similar microorganisms. Second, many of the potential bioterrorist agents are stable enough in the environment that contaminated environmental surfaces or fomites could lead to transmission of agents such as B. anthracis, F. tularensis, variola major, C. botulinum toxin, and C. burnetti (305). Third, data suggest that current disinfection and sterilization practices are appropriate for the management of patient care equipment P.1488 and environmental surfaces when potentially contaminated patients are evaluated in or admitted to a healthcare facility following exposure to a bioterrorist agent. For example, sodium hypochlorite may be used for surface disinfection (http://www.epa.gov/pesticides/factsheets/bleachfactsheet.htm). In instances where the healthcare facility is the site of a bioterrorist attack, environmental decontamination may require special decontamination procedures (e.g., chlorine dioxide gas for anthrax spores; http://www.epa.gov/pesticides/factsheets/chlorinedioxidefactsheet.htm). Use of disinfectants for decontamination following a bioterrorist attack requires crises exemption from the EPA (http://www.epa.gov/opprd001/section18/). Of only theoretical concern is the possibility that a bioterrorism agent could be engineered to be less susceptibility to disinfection and sterilization processes. Toxicologic, Environmental, and Occupational Concerns Health hazards associated with the use of germicides in healthcare vary from mucous membrane irritation to death, with the latter involving accidental injection by mentally disturbed patients (306). Although variations exist in the degree of toxicity ([Hess, 1991 #9210]; 307, 308), all disinfectants should be used with the proper safety precautions (309) and for the intended purpose only. The key factors associated with assessing the health risk of a chemical exposure include the duration, intensity (i.e., how much chemical is involved), and route (e.g., skin, mucous membranes, and inhalation) of the exposure. Toxicity may be acute or chronic. Acute toxicity usually results from an accidental spill of a chemical substance. The exposure of personnel is sudden and often produces an emergency situation. Chronic toxicity results from repeated exposure to low levels of the chemical over a prolonged period. The responsibility for informing workers of the chemical hazards in the workplace and implementing control measures rests with the employer. The OSHA Hazard Communication Standard (Code of Federal Regulations 29 CFR 1910.1200, 1915.99, 1917.28, 1918.90, 1926.59, and 1928.21) requires manufacturers and importers of hazardous chemicals to develop Material Safety Data Sheets (MSDSs) for each chemical or mixture of chemicals. Employers must have MSDSs readily available to employees who work with the products and thus may be exposed. Exposure limits have been published for many chemicals used in healthcare to aid in providing a safe environment and are discussed in each section of this chapter as relevant. Only the exposure limits published by OSHA carry the legal force of regulations. OSHA publishes a limit as a time weighted average (TWA), that is, the average concentration for a normal 8-hour workday and a 40-hour workweek to which nearly all workers may be repeatedly exposed to a chemical without adverse health effects. For example, the permissible exposure limit (PEL) for ethylene oxide is 1.0 ppm, 8-hour TWA. The National Institute for Occupational Safety and Health (NIOSH) develops recommended exposure limits (RELs). RELs are recommended by NIOSH as being protective of worker health and safety over a working lifetime. This limit is frequently expressed as a 40-hour TWA exposure for up to 10 hours per day during a 40-hour workweek. These exposure limits are designed for inhalation exposures. Irritant and allergic affects may occur below the exposure limits, and skin contact may result in dermal effects or systemic absorption apart from inhalation. The current RELs can be accessed via the NIOSH Web page (http://www.cdc.gov/niosh). Guidelines on exposure limits are also provided by the American Conference of Governmental Industrial Hygienists (ACGIH) (310). Additionally, information about workplace exposures and methods to reduce them (e.g., work practices, engineering controls, PPE) is available on the OSHA (http://www.osha.gov) and the NIOSH Web sites. Some states have excluded the disposal of certain chemical germicides (e.g., glutaraldehyde, formaldehyde, and some phenols) or limited certain concentrations via the sewer system. These rules are intended to minimize environmental harm. If healthcare facilities exceed the maximum allowable concentration for a chemical (e.g., ≥5.0 mg/L), they have three options. First, they can switch to alternative products. For example, they can change from glutaraldehyde to another disinfectant for high-level disinfection or from phenolics to quaternary ammonium compounds for low-level disinfection. Second, they can collect the disinfectant and dispose of it as a hazardous chemical. Third, they can use a commercially available small-scale treatment method (e.g., neutralize glutaraldehyde with glycine). The safe disposal of regulated chemicals is important throughout the medical community. In the case of disposal of large volumes of spent solutions, users may decide to neutralize the microbicidal activity prior to disposal (e.g., glutaraldehyde). This can be accomplished by reaction with chemicals such as sodium bisulfite (311, 312) or glycine (313). European authors have suggested that disinfection by heat rather than chemicals should be used for instruments and ventilation therapy equipment. The concerns for chemical disinfection include the toxic side effects for the patient caused by chemical residues on the instrument or object, occupational exposure to toxic chemicals, and the danger of recontamination by rinsing the disinfectant with microbially contaminated tap water (314). Disinfection in Ambulatory Care, Home Care, and the Home With the advent of managed healthcare, increasing numbers of patients are now being cared for in ambulatory care and in home settings. Many of these patients have communicable diseases, immunocompromising conditions, or invasive devices. Therefore, adequate disinfection in these settings is necessary to provide a safe patient environment. Since the ambulatory care setting (i.e., outpatient facilities) provides the same infection risk as the hospital, the Spaulding classification scheme described above should be followed (Table 85.1) (15). The home environment should be a much safer setting than hospitals or ambulatory care. Epidemics should not be a problem and cross-infection should be rare. Among the products recommended for home disinfection of reusable objects are bleach, alcohol, and hydrogen peroxide. It has been recommended by APIC that reusable objects (e.g., tracheostomy tubes) that touch mucous membranes be disinfected by immersion in 70% isopropyl alcohol for 5 minutes, or 3% hydrogen peroxide for 30 P.1489 minutes. Additionally, a 1:50 dilution of 5.25% to 6.15% sodium hypochlorite (household bleach) (3 minutes) should be effective (315, 316). Noncritical items (e.g., blood pressure cuffs, crutches) can be cleaned with a detergent. Blood spills should be handled as per OSHA regulations as described above. In general, sterilization of critical items is not practical in homes but theoretically could be accomplished by chemical sterilants or boiling. Single-use disposable items can be used or reusable items sterilized in a hospital (317, 318). Some environmental groups advocate “environmentally safe” products as alternatives to commercial germicides in the home-care setting. These alternatives (e.g., ammonia, baking soda, vinegar, Borax, liquid detergent) are not registered with the EPA and should not be used for disinfecting, because they are ineffective against S. aureus. Borax, baking soda, and detergents are also ineffective against Salmonella typhi and E. coli; however, undiluted vinegar and ammonia are effective against S. typhi and E. coli (46, 319, 320). Common commercial disinfectants designed for home use have also been found effective against selected antibiotic-resistant bacteria (46). Public concerns have been raised that the use of antimicrobials in the home may promote the development of antibiotic-resistant bacteria (321, 322). This issue is unresolved and needs to be considered further via scientific and clinical investigations. Although the public health benefits resulting from the use of disinfectants in the home environment are unknown, it is known that many sites in the home kitchen and bathroom are microbially contaminated (323), and the use of hypochlorites results in a marked reduction of bacteria (324). It is also known from laboratory studies that many commercially prepared household disinfectants are effective against common pathogens (46) and can interrupt surface-to-human transmission of pathogens (41). The “targeted hygiene concept,” which means identifying situations and areas (e.g., food preparation surfaces and bathroom) where there is a risk of transmission of pathogens, may be a reasonable way to identify when disinfection may be appropriate (325). Susceptibility of Antibiotic-Resistant Bacteria to Disinfectants As with antibiotics, reduced susceptibility (or acquired resistance) of bacteria to disinfectants can arise by either chromosomal gene mutation or the acquisition of genetic material in the form of plasmids or transposons (326, 327, 328, 329, 330, 331). When there is a change in bacterial susceptibility that renders an antibiotic ineffective against an infection previously treatable by that antibiotic, the bacteria are referred to as “resistant.” In contrast, reduced susceptibility to disinfectants does not correlate with failure of the disinfectant, because concentrations used in disinfection still greatly exceed the cidal level. Thus, the word resistance when applied to these changes is incorrect and the preferred term is reduced susceptibility or increased tolerance (329, 332). MRSA and VRE are recognized as important healthcare-associated agents. It has been known for years that some antiseptics and disinfectants are, on the basis of minimum inhibitory concentrations (MICs), somewhat less inhibitory to S. aureus strains that contain a plasmid-carrying gene encoding resistance to the antibiotic gentamicin (329). For example, Townsend et al. (333) found that gentamicin resistance also encodes reduced susceptibility to propamidine, quaternary ammonium compounds, and ethidium bromide, and Brumfitt et al. (334) found MRSA strains less susceptible than methicillin-sensitive S. aureus (MSSA) strains to chlorhexidine, propamidine, and the quaternary ammonium compound cetrimide. Al-Masaudi et al. (335) found the MRSA and MSSA strains to be equally sensitive to phenols and chlorhexidine, but MRSA strains were slightly more tolerant to quaternary ammonium compounds. Studies have established the involvement of two gene families [qacCD (now referred to as smr) and qacAB] in providing protection against agents that are components of disinfectant formulations such as quaternary ammonium compounds. Tennent et al. (336) propose that staphylococci evade destruction because the protein specified by the qacA determinant is a cytoplasmic-membrane–associated protein involved in an efflux system that actively reduces intracellular accumulation of toxicants such as quaternary ammonium compounds to intracellular targets. Other studies demonstrated that plasmid-mediated formaldehyde tolerance is transferable from Serratia marcescens to E. coli (337) and plasmid-mediated quaternary ammonium tolerance is transferable from S. aureus to E. coli (338). Tolerance to mercury and silver is also plasmid borne (326, 328, 329, 330, 331). Since the concentrations of disinfectants used in practice are much higher than the MICs observed, even for the more tolerant strains, the clinical relevance of these observations is questionable. Several studies have found antibiotic-resistant hospital strains of common healthcare-associated pathogens (i.e., Enterococcus, P. aeruginosa, Klebsiella pneumoniae, E. coli S. aureus, and S. epidermidis) to be equally susceptible to disinfectants as antibiotic-sensitive strains (46, 339, 340, 341). The susceptibility of glycopeptide-intermediate S. aureus was similar to vancomycin-susceptible MRSA (342). Based on these data, routine disinfection and housekeeping protocols do not need to be altered because of antibiotic resistance provided the disinfection method is effective (343, 344). A study that evaluated the efficacy of selected cleaning methods (e.g., QUAT-sprayed cloth, and QUAT-immersed cloth) for eliminating VRE found that currently used disinfection processes are likely highly effective in eliminating VRE. However, surface disinfection must involve contact with all contaminated surfaces (343). Lastly, does the use of antiseptics or disinfectants facilitate the development of disinfectant-tolerant microorganisms? Based on current evidence and reviews (321, 322, 331, 332, 345), the development of enhanced tolerance to disinfectants in response to disinfectant exposure can occur. However, it is not important in clinical terms since the level of tolerance is low and unlikely to compromise the effectiveness of disinfectants where much higher concentrations are used (332). The issue of whether low-level tolerance to germicides selects for antibiotic-resistant strains is unsettled but may depend on the mechanism by which tolerance is attained. For example, changes in the permeability barrier or efflux mechanisms may affect susceptibility to antibiotics and germicides, but specific changes to a target site may not. Some researchers have suggested that the use of disinfectants or antiseptics (e.g., triclosan) could facilitate the development of antibiotic-resistant microorganisms (321, 322, 346). P.1490 Although there is evidence in laboratory studies of low-level resistance to triclosan, the concentrations of triclosan in these studies were low (generally <1 Вg/mL) and dissimilar from the higher levels used in antimicrobial products (2,000–20,000 Вg/mL) (347, 348). Thus, researchers can create laboratory-derived mutants that demonstrate reduced susceptibility to antiseptics or disinfectants. In some experiments, such bacteria have demonstrated reduced susceptibility to certain antibiotics (322). There is no evidence that using antiseptics/disinfectants selects for antibiotic-resistant microorganisms in nature or that mutants survive in nature (349). In addition, there are fundamental differences between the action of antibiotics and disinfectants. Antibiotics are selectively toxic and generally have a single target site in bacteria, thereby inhibiting a specific biosynthetic process. Germicides generally are considered to be nonspecific antimicrobials because of a multiplicity of toxic effect mechanisms or target sites and are broader spectrum in the types of microorganisms against which they are effective (329, 332). The rotational use of disinfectants in some environments (e.g., pharmacy production units) has been recommended and practiced in an attempt to prevent the development of resistant microbes (350, 351). Currently, there are rare case reports about appropriately used disinfectants that have resulted in a clinical problem arising from the selection or development of nonsusceptible microorganisms (352). Surface Disinfection: Should We Do It? The effective use of disinfectants constitutes an important factor in preventing healthcare-associated infections. Surfaces are considered noncritical items as they come in contact with intact skin. Use of noncritical items or contact with noncritical surfaces carries little risk of transmitting a pathogen to patients or staff. Thus, the routine use of germicidal chemicals to disinfect hospital floors and other noncritical items is controversial (353, 354). In 1991, Favero and Bond (355) provided an expansion of the Spaulding scheme by dividing the noncritical environmental surfaces into housekeeping surfaces and medical equipment surfaces. The classes of disinfectants used on housekeeping and medical equipment surfaces may be similar. However, the frequency of decontaminating may vary (see manufacturers' recommendations). Medical equipment surfaces (e.g., blood pressure cuffs, stethoscopes, hemodialysis machines, and x-ray machines) may become contaminated with infectious agents and may contribute to the spread of healthcare-associated infections (224). For this reason, noncritical medical equipment surfaces should be disinfected with an EPA-registered low- or intermediate-level disinfectant. Use of a disinfectant provides antimicrobial activity that is likely to be achieved with minimal additional cost or work. Environmental surfaces (e.g., bedside table) also may potentially contribute to cross-transmission by hand contamination of healthcare personnel due to contact with contaminated surfaces, medical equipment, or patients (44, 356). A recent paper reviews the epidemiologic and microbiologic data regarding the use of disinfectants on noncritical surfaces (357). Table 85.6 lists seven reasons for using a disinfectant on noncritical surfaces. Five of these are particularly noteworthy and support the use of a germicidal detergent. First, hospital floors become contaminated with microorganisms by settling of airborne bacteria; by contact with shoes, wheels, and other objects; and occasionally by spills. The removal of microbes is a component in the control of healthcare-associated infections. In an investigation on the cleaning of hospital floors, the use of soap and water (90% reduction) was less effective in reducing the numbers of bacteria than was a phenolic disinfectant (94–99.9% reduction) (358). However, a few hours after floor disinfection the bacterial count was nearly back to the pretreatment level. Second, detergents become contaminated and result in seeding the patient's environment with bacteria. Investigators have shown that mop water becomes increasingly dirty during cleaning, and mop water becomes contaminated if soap and water is used rather than a disinfectant. For example, Ayliffe et al. (359) found that bacterial contamination in soap and water without a disinfectant increased from 10 to 34,000 CFU/mL after cleaning a ward, whereas the contamination in a disinfectant solution did not change (20 CFU/mL). Dharan et al. (360) also found that the use of detergents on floors and patient room furniture increased the bacterial contamination in the patients' environmental surfaces after cleaning (average increase = 103.6 CFU/24 cm2) (360). In addition, Engelhart et al. (361) recently described a P. aeruginosa outbreak in a hematology-oncology unit associated with contamination of the surface cleaning equipment when nongermicidal cleaning solutions instead of disinfectants P.1491 were used for decontamination of the patients' environment. Third, the CDC recommends in its isolation guideline that noncritical equipment contaminated with blood, body fluids, secretions, or excretions be cleaned and disinfected after use. The same guideline recommends that, in addition to cleaning, disinfection of the bedside equipment and environmental surfaces (e.g., bed rails, bedside tables, carts, commodes, doorknobs, and faucet handles) is indicated for certain pathogens, especially enterococci, which can survive in the inanimate environment for prolonged periods (362). Fourth, OSHA requires that surfaces contaminated with blood and other potentially infectious materials (e.g., amniotic, pleural fluid) be disinfected. Fifth, using a single product throughout the facility may simplify both training and appropriate practice. TABLE 85.6. EPIDEMIOLOGIC EVIDENCE ASSOCIATED WITH THE USE OF SURFACE DISINFECTANTS OR DETERGENTS ON NONCRITICAL SURFACES Justification for Use of Disinfectants for Noncritical Surfaces Surfaces may contribute to transmission of epidemiologically important microbes (e.g., vancomycin-resistant Enterococcus, methicillin-resistant S. aureus, viruses) Disinfectants are needed for surfaces contaminated by blood and other potentially infective material Disinfectants are more effective than detergents in reducing microbial load on floors Detergents become contaminated and result in seeding the patient's environment with bacteria Disinfection of noncritical equipment and surfaces is recommended for patients on isolation precautions by the Centers for Disease Control and Prevention. Advantage of using a single product for decontamination of noncritical surfaces, both floors and equipment Some newer disinfectants have persistent antimicrobial activity Justification for Using a Detergent on Floors Noncritical surfaces contribute minimally to endemic healthcare-associated infections No difference in healthcare-associated infection rates when floors are cleaned with detergent versus disinfectant No environmental impact (aquatic or terrestrial) issues with disposal No occupational health exposure issues Lower costs Use of antiseptics/disinfectants selects for antibiotic-resistant bacteria (?) More aesthetically pleasing floor Modified from 357. There also are reasons for using a detergent alone on floors since noncritical surfaces contribute minimally to endemic healthcare-associated infections (363), and no differences have been found in healthcare-associated infection rates when floors are cleaned with detergent versus disinfectant (360, 364, 365). However, these studies have been small, of short duration, and suffer from low statistical power since the outcome, healthcare-associated infections, is one of low frequency. The low rate of infections makes it difficult statistically to demonstrate the efficacy of an intervention. Since housekeeping surfaces are associated with the lowest risk of disease transmission, some researchers have suggested that either detergents or a disinfectant/detergent could be used (355). Although there are no data that demonstrate a reduction in healthcare-associated infection rates with the use of surface disinfection of floors, there are data that demonstrate a reduction in microbial load associated with the use of disinfectants. Given this information and that environmental surfaces (e.g., bedside table, bed rails) in close proximity to the patient and in outpatient settings (366) have been demonstrated to become contaminated with epidemiologically important microbes such as VRE and MRSA (40, 366, 367, 368) and these microorganisms survive on various hospital surfaces (369, 370), some have suggested that these surfaces should be disinfected on a regularly scheduled basis (357). Spot decontamination on fabrics that remain in hospitals or clinic rooms while patients move in and out (e.g., privacy curtains) also should be considered. One study demonstrated the effectiveness of spraying the fabric with 3% hydrogen peroxide (371). Future studies should evaluate the level of contamination on noncritical environmental surfaces as a function of high and low hand contact and whether some surfaces (e.g., bed rails) near the patient with high contact frequencies require more frequent disinfection. Regardless of whether a detergent or disinfectant is used on surfaces in a healthcare facility, cleaning should be undertaken on a routine basis and when environmental surfaces are dirty or soiled in order to provide an aesthetically pleasing environment and to prevent potentially contaminated objects from serving as a source for healthcare-associated infections (372). The value of designing surfaces (e.g., hexyl-polyvinylpyridine) that kill bacteria on contact (373) or have sustained antimicrobial activity (374) should be further evaluated. Heavy microbial contamination of wet mops and cleaning cloths and the potential for spread of such contamination have been recognized by several investigators (59, 375). They have shown that wiping hard surfaces with contaminated cloths may result in contamination of hands, equipment, and other surfaces (59, 376). Data have been published that can be used to formulate effective policies for decontamination and maintenance of reusable cleaning cloths. For example, heat was the most reliable treatment of cleaning cloths as a detergent washing followed by drying at 80ВC for 2 hours produced elimination of contamination. Alternatively, immersing the cloth in hypochlorite (4,000 ppm) for 2 minutes produced no detectable survivors in 10 of 13 cloths (377). If reusable cleaning cloths or mops are used, decontamination should occur regularly to prevent surface contamination during cleaning with subsequent transfer of microorganisms from these surfaces to patients or equipment via the hands of healthcare workers. Air Disinfection The use of a disinfectant spray-fog technique for antimicrobial control of hospital rooms has been used. This technique of spraying of disinfectants is an unsatisfactory method of decontaminating air and surfaces and is not recommended for general infection control in routine patient-care areas (362). Disinfectant fogging is rarely, if ever, used in U.S. healthcare facilities for air and surface disinfection in patient-care areas. Methods (e.g., filtration, ultraviolet germicidal irradiation, chlorine dioxide) to reduce air contamination in the healthcare setting are discussed in another guideline (21). Microbial Contamination of Disinfectants Contaminated disinfectants and antiseptics have been occasional vehicles of healthcare infections and pseudoepidemics for more than 50 years. A summary of the published reports describing contaminated disinfectants and antiseptic solutions leading to healthcare-associated infections has been published (378). Since this summary, additional reports have been published (379, 380, 381). When examining the reports of disinfectants found contaminated with microorganisms, there are several noteworthy observations. Perhaps most importantly, high-level disinfectants/liquid chemical sterilants have not been associated with outbreaks due to intrinsic or extrinsic contamination. Another feature of these outbreaks has been that members of the genus Pseudomonas (e.g., P. aeruginosa) are the most frequent isolates from contaminated disinfectants, being the agents recovered from 80% of the contaminated products. Their ability to remain viable or grow in use-dilutions of disinfectants is unparalleled. This survival advantage for Pseudomonas is presumably due to their nutritional versatility, their unique outer membrane that constitutes an effective barrier to the passage of germicides, and/or their efflux systems. Although the concentrated solutions of the disinfectants have not been demonstrated to be contaminated at the point of manufacture, Newman et al. (382) found that an undiluted phenolic may be contaminated by a Pseudomonas species during use. In most of the reports that describe illness associated with contaminated disinfectants, the product was used to disinfect patient-care equipment such as cystoscopes, cardiac catheters, and thermometers. The germicides used as disinfectants P.1492 that were reported contaminated include chlorhexidine, quaternary ammonium compounds, phenolics, and pine oil. The following control measures should be instituted to reduce the frequency of bacterial growth in disinfectants and the threat of serious healthcare-associated infections from the use of such contaminated products (378). First, some disinfectants should not be diluted and those that are must be prepared correctly to achieve the manufacturer's recommended use-dilution. Second, we must learn from the literature what inappropriate activities result in extrinsic contamination (i.e., at the point of use) of germicides and prevent their recurrence. Common sources of extrinsic contamination of germicides in the reviewed literature are the water to make working dilutions, contaminated containers, and general contamination of the hospital areas where the germicides are prepared and/or used. Third, stock solutions of germicides must be stored as indicated on the product label. Currently, the EPA verifies manufacturers' efficacy claims against microorganisms. These measures should provide assurance that products that meet the EPA registration requirements are capable of achieving a certain level of antimicrobial activity when used as directed. FACTORS AFFECTING THE EFFICACY OF DISINFECTION AND STERILIZATION The activity of germicides against microorganisms depends on a number of factors, some of which are intrinsic qualities of the microorganism, whereas others depend on the chemical and external physical environment. An awareness of these factors should lead to a better utilization of disinfection and sterilization processes; thus they will be briefly reviewed. More extensive consideration of these and other factors may be found elsewhere (11, 12, 14, 383, 384). Number and Location of Microorganisms All other conditions remaining constant, the larger the number of microbes present, the longer it takes for a germicide to destroy all of them. This relationship was illustrated by Spaulding when he employed identical test conditions and demonstrated that it took 30 minutes to kill 10 B. atrophaeus (formerly Bacillus subtilis) spores but 3 hours to kill 100,000 B. atrophaeus spores. This reinforces the need for scrupulous cleaning of medical instruments before disinfection and sterilization. By reducing the number of microorganisms that must be inactivated, one correspondingly shortens the exposure time required to kill the entire microbial load. Researchers have also shown that aggregated or clumped cells are more difficult to inactivate than monodispersed cells (385). The location of microorganisms also must be considered when assessing factors affecting the efficacy of germicides. Medical instruments with multiple pieces must be disassembled, and equipment such as endoscopes that have crevices, joints, and channels are more difficult to disinfect than flat-surface equipment, because it is more difficult to penetrate all parts of the equipment with a disinfectant. Only surfaces in direct contact with the germicide will be disinfected, so there must be no air pockets, and the equipment must be completely immersed for the entire exposure period. Manufacturers should be encouraged to produce equipment that is engineered so cleaning and disinfection may be accomplished with ease. Innate Resistance of Microorganisms Microorganisms vary greatly in their resistance to chemical germicides and sterilization processes (Fig. 85.1) (327). Intrinsic resistance mechanisms in microorganisms to disinfectants varies. For example, spores are resistant to disinfectants, because the spore coat and cortex act as a barrier, mycobacteria have a waxy cell wall that prevents disinfectant entry, and gram-negative bacteria possess an outer membrane that acts as a barrier to the uptake of disinfectants (326, 328, 329, 330). Implicit in all disinfection strategies is the consideration that the most resistant microbial subpopulation controls the sterilization or disinfection time. That is, to destroy the most resistant types of microorganisms-bacterial spores, the user needs to employ exposure times and a concentration of germicide needed to achieve complete destruction. With the exception of prions, bacterial spores possess the highest innate resistance to chemical germicides, followed by coccidia (e.g., Cryptosporidium), mycobacteria (e.g., M. tuberculosis), nonlipid or small viruses (e.g., poliovirus, and coxsackievirus), fungi (e.g., Aspergillus and Candida), vegetative bacteria (e.g., Staphylococcus and Pseudomonas), and lipid or medium-size viruses (e.g., herpes and HIV). The germicidal resistance exhibited by the gram-positive and gram-negative bacteria is similar with some exceptions (e.g., P. aeruginosa, which shows greater resistance to some disinfectants) (352, 386, 387). P. aeruginosa has also been shown to be significantly more resistant to a variety of disinfectants in its naturally occurring state as compared to cells subcultured on laboratory media (386). Rickettsiae, Chlamydiae, and mycoplasma cannot be placed in this scale of relative resistance, because information on the efficacy of germicides against these agents is limited (388). Since these microorganisms contain lipid and are similar in structure and composition to other bacteria, it might be predicted that they would be inactivated by the same germicides that destroy lipid viruses and vegetative bacteria. A known exception to this supposition is Coxiella burnetti, which has demonstrated resistance to disinfectants (389). Figure 84.1. Protective garb worn by healthcare workers in the Middle Ages to protect themselves against plague. Concentration and Potency of Disinfectants With other variables constant, and with one exception (i.e., iodophors), the more concentrated the disinfectant, the greater its efficacy and the shorter the time necessary to achieve microbial kill. Generally not recognized, however, is that all disinfectants are not similarly affected by concentration adjustments. For example, quaternary ammonium compounds and phenol have a concentration exponent of 1 and 6, respectively; thus halving the concentration of a quaternary ammonium compound requires a doubling of its disinfecting time, but halving the concentration of a phenol solution requires a 64-fold (i.e., 26) increase in its disinfecting time (348, 390). It is also important to consider the length of the disinfection time, which is dependent on the potency of the germicide. This P.1493 was illustrated by Spaulding, who demonstrated using the mucin-loop test that 70% isopropyl alcohol destroyed 104 M. tuberculosis in 5 minutes, whereas a simultaneous test with 3% phenolic required 2 to 3 hours to achieve the same level of microbial kill (12). Physical and Chemical Factors Several physical and chemical factors—temperature, pH, relative humidity, and water hardness—also influence disinfectant procedures. For example, the activity of most disinfectants increases as the temperature increases but there are exceptions. Further, too great an increase in temperature causes the disinfectant to degrade, weakens its germicidal activity, and may produce a potential health hazard. An increase in pH improves the antimicrobial activity of some disinfectants (e.g., glutaraldehyde, quaternary ammonium compounds) but decreases the antimicrobial activity of others (phenols, hypochlorites, and iodine). The pH influences the antimicrobial activity by altering the disinfectant molecule or the cell surface. Relative humidity is the single most important factor influencing the activity of gaseous disinfectants/sterilants such as ETO, chlorine dioxide, and formaldehyde. Water hardness (i.e., high concentration of divalent cations) reduces the rate of kill of certain disinfectants. This occurs because divalent cations (e.g., magnesium and calcium) in the hard water interact with the disinfectant to form insoluble precipitates (11, 391). Organic and Inorganic Matter Organic matter in the form of serum, blood, pus, fecal, or lubricant material may interfere with the antimicrobial activity of disinfectants in at least two ways. Most commonly the interference occurs by a chemical reaction between the germicide and the organic matter, resulting in a complex that is less germicidal or nongermicidal, leaving less of the active germicide available for attacking microorganisms. Chlorine and iodine disinfectants, in particular, are prone to such interaction. Alternatively, organic material may protect microorganisms from attack by acting as a physical barrier (392). The effects of inorganic contaminants on the sterilization process were studied in the 1950s and 1960s (393, 394). These studies and more recent studies show the protection of microorganisms to all sterilization processes due to occlusion in salt crystals (244, 395). This further emphasizes the importance of meticulous cleaning of medical devices before any sterilization or disinfection procedure since both organic and inorganic soils are easily removed by washing (244). P.1494 Duration of Exposure Items must be exposed to the appropriate germicide for the minimum contact time specified on the products labeling unless scientific studies demonstrate an alternative time is effective. All lumina and channels of endoscopic instruments must come in contact with the disinfectant. Air pockets interfere with the disinfection process and items that float on the disinfectant will not be disinfected. The disinfectant must be introduced reliably into the internal channels of the device. The exact times for disinfecting medical items are somewhat elusive because of the effect of the aforementioned factors on disinfection efficacy. Contact times that have proved reliable are presented in Table 85.1, but, in general, the longer contact times are more effective than shorter ones. Biofilms Microorganisms may be protected from disinfectants due to the production of thick masses of cells (396) and extracellular materials or biofilms (397, 398, 399, 400, 401, 402, 403). Biofilms are microbial masses attached to surfaces that are immersed in liquids. Once these masses are formed, microbes may be resistant to the disinfectants by multiple mechanisms including higher resistance of older biofilms, genotypic variation of the bacteria, microbial production of neutralizing enzymes, and physiologic gradients within the biofilm (e.g., pH). Although new decontamination methods are being investigated for removal of biofilms, chlorine remains the most efficient product (404). Investigators have hypothesized that the glycocalyx-like cellular masses on the interior walls of polyvinyl chloride pipe would protect embedded microorganisms from some disinfectants and serve as a reservoir for continuous contamination (397, 398, 405). Biofilms have been found in whirlpools (406), dental unit waterlines (407), and numerous medical devices (e.g., contact lenses, pacemakers, hemodialysis systems, urinary catheters, central venous catheters, endoscopes) (402, 404, 408). Their presence may have serious implications for immunocompromised patients and patients with indwelling medical devices. Enzymes can be used for the degradation of biofilms (409), but no products are registered by the EPA or FDA for this purpose. CHEMICAL DISINFECTANTS Alcohol Overview In the healthcare setting, “alcohol” refers to two water-soluble chemical compounds whose germicidal characteristics are generally underrated: ethyl alcohol and isopropyl alcohol (410). These alcohols are rapidly bactericidal rather than bacteriostatic against vegetative forms of bacteria; they also are tuberculocidal, fungicidal, and virucidal but do not destroy bacterial spores. Their cidal activity drops sharply when diluted below 50% concentration, and the optimum bactericidal concentration is in the range of 60% to 90% solutions in water (volume/volume) (411, 412). Mode of Action The most feasible explanation for the antimicrobial action of alcohol is denaturation of proteins. This is supported by the observation that absolute ethyl alcohol, a dehydrating agent, is less bactericidal than mixtures of alcohol and water, because proteins are denatured more quickly in the presence of water (412, 413). Protein denaturation also is consistent with the observations by Sykes (414) that alcohol destroys the dehydrogenases of E. coli, and Dagley et al. (415) that ethyl alcohol increases the lag phase of Enterobacter aerogenes and this could be reversed by the addition of certain amino acids. The latter authors concluded that the bacteriostatic action was due to the inhibition of the production of metabolites essential for rapid cell division. Microbicidal Activity Methyl alcohol (methanol) has the weakest bactericidal action of the alcohols and thus is seldom used in healthcare (416). The bactericidal activity of various concentrations of ethyl alcohol (ethanol) was examined by Morton (411) against a variety of microorganisms in exposure periods ranging from 10 seconds to 1 hour. P. aeruginosa was killed in 10 seconds by all concentrations of ethanol from 30% to 100% (v/v), whereas S. marcescens, E. coli, and Salmonella typhosa were killed in 10 seconds by all concentrations of ethanol from 40% to 100%. The gram-positive microorganisms S. aureus and Streptococcus pyogenes were slightly more resistant, being killed in 10 seconds by ethyl alcohol concentrations from 60% to 95%. Coulthard and Sykes (417) found isopropyl alcohol (isopropanol) slightly more bactericidal than ethyl alcohol for E. coli and S. aureus. Ethyl alcohol, at concentrations of 60% to 80%, is a potent virucidal agent inactivating all of the lipophilic viruses (e.g., herpes, vaccinia, influenza virus) and many hydrophilic viruses [e.g., adeno-, entero-, rhino-, and rotaviruses but not hepatitis A virus (51)]. Isopropyl alcohol is not active against the nonlipid enteroviruses but is fully active against the lipid viruses (63). Studies also have demonstrated the ability of ethyl and isopropyl alcohol to inactivate HBV (203, 204) and the herpes virus (418), and ethyl alcohol to inactivate HIV (206), rotavirus, echovirus, and astrovirus (419). In testing the effect of ethyl alcohol against M. tuberculosis, Smith (420) noted that 95% ethanol killed the tubercle bacilli in sputum or water suspension within 15 seconds. In 1964, Spaulding stated that alcohols were the germicide of choice for tuberculocidal activity and they should be the standard by which all other tuberculocides were compared. For example, he compared the tuberculocidal activity of iodophor (450 ppm), a substituted phenol (3%), and isopropanol (70%/volume) using the mucin-loop test (106 M. tuberculosis per loop) and determined that the contact times needed for complete destruction were 120 to 180 minutes, 45 to 60 minutes, and 5 minutes, respectively. The mucin-loop test is a severe test developed for the purpose of producing long survival times. Thus, these figures should not be extrapolated to the exposure times that are needed when these germicides are being used on medical or surgical material (410). Ethyl alcohol (70%) was the most effective concentration for killing the tissue phase of Cryptococcus neoformans, Blastomyces P.1495 dermatitidis, Coccidioides immitis, and Histoplasma capsulatum and the culture phases of the latter three microorganisms aerosolized onto various surfaces. The culture phase was more resistant to the action of ethyl alcohol and required about 20 minutes to disinfect the contaminated surface, compared to <1 minute for the tissue phase (421, 422). Isopropyl alcohol (20%) has been shown to be effective in killing the cysts of Acanthamoeba culbertsoni (423) as have chlorhexidine, hydrogen peroxide, and thimerosal (424). Uses Alcohols are not recommended for sterilizing medical and surgical materials principally because of their lack of sporicidal action and their inability to penetrate protein-rich materials. Fatal postoperative wound infections with Clostridium have occurred when alcohols were used to sterilize surgical instruments contaminated with bacterial spores (425). Alcohols have been used effectively to disinfect oral and rectal thermometers (426, 427), hospital pagers (428), scissors (429), stethoscopes (430), and fiberoptic endoscopes (431, 432). Alcohol towelettes have been used for years to disinfect small surfaces such as rubber stoppers of multiple-dose medication vials or vaccine bottles. Furthermore, alcohol is occasionally used to disinfect external surfaces of equipment [e.g., stethoscopes, ventilators, manual ventilation bags (433)], CPR manikins (434), ultrasound instruments (435), or medication preparation areas. Two studies demonstrated the effectiveness of 70% isopropyl alcohol to disinfect reusable transducer heads in a controlled environment (436, 437). In contrast, Beck-Sague and Jarvis (438) described three bloodstream infection outbreaks when alcohol was used to disinfect transducer heads in an intensive care setting. The documented shortcomings of alcohols on equipment are that they damage the shellac mountings of lensed instruments, tend to swell and harden rubber and certain plastic tubing after prolonged and repeated use, bleach rubber and plastic tiles (410), and damage tonometer tips (deterioration of the glue) after the equivalent of one working year of routine use (439). Lingel and Coffey (440) also found that tonometer biprisms soaked in alcohol for 4 days developed rough front surfaces that could potentially cause corneal damage. This appeared to be caused by a weakening of the cementing substances used to fabricate the biprisms. Corneal opacification has been reported when tonometer tips were swabbed with alcohol immediately before intraocular pressure measurements were taken (441). Alcohols are flammable and consequently must be stored in a cool, well-ventilated area. They also evaporate rapidly, and this makes extended exposure time difficult to achieve unless the items are immersed. Chlorine and Chlorine Compounds Overview Hypochlorites are the most widely used of the chlorine disinfectants and are available in a liquid (e.g., sodium hypochlorite) or solid (e.g., calcium hypochlorite) form. The most prevalent chlorine products in the U.S. are aqueous solutions of 5.25% to 6.15% sodium hypochlorite, which usually are called household bleach. They have a broad spectrum of antimicrobial activity, do not leave toxic residues, are unaffected by water hardness, are inexpensive and fast acting (316), remove dried or fixed microorganisms and biofilms from surfaces (245), and have a low incidence of serious toxicity (442, 443, 444). Sodium hypochlorite at the concentration used in domestic bleach (5.25–6.15%) may produce ocular irritation or oropharygeal, esophageal, and gastric burns (307, 445, 446, 447, 448, 449). Other disadvantages of hypochlorites include corrosiveness to metals in high concentrations (>500 ppm), inactivation by organic matter, discoloring or “bleaching” of fabrics, release of toxic chlorine gas when mixed with ammonia or acid (e.g., household cleaning agents) (450, 451, 452), and relative instability (315). The microbicidal activity of chlorine largely is attributed to undissociated hypochlorous acid (HOCl). The dissociation of HOCl to the less microbicidal form (hypochlorite ion OCl-) is dependent on pH. The disinfecting efficacy of chlorine decreases with an increase in pH that parallels the conversion of undissociated HOCl to hypochlorite ion (453, 454). A potential hazard is the production of the carcinogen bis-chloromethyl ether when hypochlorite solutions come into contact with formaldehyde (455) and the production of the animal carcinogen trihalomethane when hot water is hyperchlorinated (456). The EPA has decided after reviewing environmental fate and ecologic data that the currently registered uses of hypochlorites will not result in unreasonable adverse effects to the environment (457). Alternative compounds that release chlorine and are used in the healthcare setting include demand-release chlorine dioxide, sodium dichloroisocyanurate, and chloramine T. The advantage of these compounds over the hypochlorites is that they retain chlorine longer and so exert a more prolonged bactericidal effect. Sodium dichloroisocyanurate tablets are stable, and the microbicidal activity of solutions prepared from sodium dichloroisocyanurate tablets may be greater than that of sodium hypochlorite solutions containing the same total available chlorine for two reasons. First, with sodium dichloroisocyanurate only 50% of the total available chlorine present is free (HOCl and OCl-), whereas the remainder is combined (mono- or dichloroisocyanurate), and as free available chlorine is used up the latter is released to restore the equilibrium. Second, solutions of sodium dichloroisocyanurate are acidic whereas sodium hypochlorite solutions are alkaline and the more microbicidal type of chlorine (HOCl) is believed to predominate (458, 459, 460, 461). Disinfectants based on chlorine dioxide are prepared fresh as required by mixing the two components [base solution (citric acid with preservatives and corrosion inhibitors) and the activator solution (sodium chlorite)]. In vitro suspension tests showed that solutions containing about 140 ppm chlorine dioxide achieved a reduction factor exceeding 106 of S. aureus in 1 minute and of B. atrophaeus spores in 2.5 minutes in the presence of 3 g/L bovine albumin. The potential for damaging equipment requires consideration as long-term use can result in damage to the outer plastic coat of the insertion tube (462). Mode of Action The exact mechanism by which free chlorine destroys microorganisms has not been elucidated. Inactivation by chlorine may P.1496 result from a number of factors: oxidation of sulfhydral enzymes and amino acids; ring chlorination of amino acids; loss of intracellular contents; decreased uptake of nutrients; inhibition of protein synthesis; decreased oxygen uptake; oxidation of respiratory components; decreased adenosine triphosphate production; breaks in DNA; and depressed DNA synthesis (332, 454). The actual microbicidal mechanism of chlorine may involve a combination of these factors or the effect of chlorine on critical sites (332). Microbicidal Activity Low concentrations of free available chlorine (e.g., HOCl, OCl-, and elemental chlorine—Cl2) have a biocidal effect on mycoplasma (25 ppm) and vegetative bacteria (<5 ppm) in seconds in the absence of an organic load (388, 454). Higher concentrations (1,000 ppm) of chlorine are required to kill M. tuberculosis using the Association of Official Analytical Chemists (AOAC) tuberculocidal test (64). A concentration of 100 ppm will kill ≥99.9% of B. atrophaeus spores within 5 minutes (463, 464) and destroy mycotic agents in <1 hour (454). Klein and DeForest (63) reported that 25 different viruses were inactivated in 10 minutes with 200 ppm available chlorine. Several studies have demonstrated the effectiveness of diluted sodium hypochlorite and other disinfectants to inactivate HIV (54). Chlorine (500 ppm) showed inhibition of Candida after 30 seconds of exposure (47). Experiments using the AOAC use-dilution method have shown that 100 ppm of free chlorine will kill 106 to 107 S. aureus, Salmonella choleraesuis, and P. aeruginosa in <10 minutes (315). Since household bleach contains from 5.25% to 6.15% sodium hypochlorite, or 52,500 to 61,500 ppm available chlorine, a 1:1,000 dilution provides about 53 to 62 ppm available chlorine and a 1:10 dilution of household bleach provides about 5,250 to 6,150 ppm. Some data are available for chlorine dioxide that support manufacturers' bactericidal, fungicidal, sporicidal, tuberculocidal, and virucidal label claims (465, 466, 467, 468). A chlorine dioxide generator has been shown effective for decontamination of flexible endoscopes (462). Chlorine dioxide can be produced by mixing solutions such as a solution of chlorine with a solution of sodium chlorite (454). In 1986 a chlorine dioxide product was voluntarily removed from the market when its use was found to cause cellulose-based dialyzer membranes to leak, which allowed bacteria to migrate from the dialysis fluid side of the dialyzer to the blood side (469). Sodium dichloroisocyanurate at 2,500 ppm available chlorine has been found to be effective against bacteria in the presence of up to 20% plasma compared to 10% plasma for sodium hypochlorite at 2,500 ppm (470). Uses Hypochlorites are widely used in healthcare facilities in a variety of settings (316). Inorganic chlorine solution is used for disinfecting tonometer heads (162) and for spot disinfection of counter tops and floors. A 1:10 to 1:100 dilution of 5.25% to 6.15% sodium hypochlorite (i.e., household bleach) (20, 207, 471, 472) or an EPA-registered tuberculocidal disinfectant (15) has been recommended for decontaminating blood spills. For small spills of blood (i.e., drops of blood) on noncritical surfaces, the area can be disinfected with a 1:100 dilution of 5.25% to 6.15% sodium hypochlorite or an EPA-registered tuberculocidal disinfectant. Since hypochlorites and other germicides are substantially inactivated in the presence of blood (56, 470, 473, 474), large spills of blood require that the surface be cleaned before an EPA-registered disinfectant or a 1:10 (final concentration) solution of household bleach is applied. If there is a possibility of a sharps injury, there should be an initial decontamination (60, 307), followed by cleaning and terminal disinfection (1:10 final concentration) (56). Extreme care should always be employed to prevent percutaneous injury. At least 500 ppm available chlorine for 10 minutes is recommended for decontamination of CPR training manikins (475). Full-strength bleach is recommended for self-disinfection of needles and syringes used for illicit drug use when needle exchange programs are not available. The difference in the recommended concentrations of bleach reflects the difficulty of cleaning the interior of needles and syringes and the use of needles and syringes for parenteral injection (476). Clinicians should not alter their use of chlorine on environmental surfaces based on testing methodologies that do not simulate actual disinfection practices (477, 478). Other uses in healthcare include as an irrigating agent in endodontic treatment (479) and for disinfecting manikins, laundry, dental appliances, hydrotherapy tanks (21, 36), regulated medical waste before disposal (316), and the water distribution system in hemodialysis centers and hemodialysis machines (221). Chlorine has long been favored as the preferred disinfectant in water treatment. Hyperchlorination of a Legionella-contaminated hospital water system (21) resulted in a dramatic decrease (30% to 1.5%) in the isolation of L. pneumophila from water outlets and a cessation of healthcare-associated Legionnaires' disease in the affected unit (456, 480). Chloramine T (481) and hypochlorites (36) have been used in disinfecting hydrotherapy equipment. Hypochlorite solutions in tap water at a pH >8 stored at room temperature (23ВC) in closed, opaque plastic containers may lose up to 40% to 50% of their free available chlorine level over a period of 1 month. Thus, if a user wished to have a solution containing 500 ppm of available chlorine at day 30, a solution containing 1,000 ppm of chlorine should be prepared at time 0. There is no decomposition of sodium hypochlorite solution after 30 days when stored in a closed brown bottle (315). The use of powders, composed of a mixture of a chlorine-releasing agent with highly absorbent resin, for disinfecting body fluid spills has been evaluated by laboratory tests and hospital ward trials. The inclusion of acrylic resin particles in formulations markedly increases the volume of fluid that can be soaked up as the resin can absorb 200 to 300 times its own weight of fluid, depending on the fluid consistency. When experimental formulations containing 1%, 5%, and 10% available chlorine were evaluated by a standardized surface test, those containing 10% demonstrated bactericidal activity. One problem with chlorine-releasing granules is that chlorine fumes can be generated when they are applied to urine (482). P.1497 Formaldehyde Overview Formaldehyde is used as a disinfectant and sterilant both in the liquid and gaseous states. The liquid form is considered briefly here, and a review of the gaseous form may be found elsewhere (483). Formaldehyde is sold and used principally as a water-based solution called formalin, which is 37% formaldehyde by weight. The aqueous solution is a bactericide, tuberculocide, fungicide, virucide, and sporicide (63, 73, 484, 485, 486). OSHA indicated that formaldehyde should be handled in the workplace as a potential carcinogen and set an employee exposure standard for formaldehyde that limits an 8-hour TWA exposure to a concentration of 0.75 parts formaldehyde per million parts of air (0.75 ppm) (487, 488). The standard includes a second permissible exposure limit in the form of a short-term exposure limit (STEL) of 2 ppm that is the maximum exposure allowed during a 15-minute period (489). Ingestion of formaldehyde can be fatal, and long-term exposure to low levels in the air or on the skin can cause asthma-like respiratory problems and skin irritation such as dermatitis and itching. For these reasons, employees should have limited direct contact with formaldehyde, and these considerations limit its role in sterilization and disinfection processes. Key provisions of the OSHA standard that protects workers from exposure to formaldehyde can be found in Title 29 of CFR 1910.1048 (and equivalent regulations in states with OSHA-approved state plans) (490). Mode of Action Formaldehyde inactivates microorganisms by alkylating the amino and sulfhydral groups of proteins and ring nitrogen atoms of purine bases (355). Microbicidal Activity A wide range of microorganisms are destroyed by varying concentrations of aqueous formaldehyde solutions. Klein and DeForest (63) demonstrated inactivation of poliovirus in 10 minutes required an 8% concentration of formalin, but all other viruses tested were inactivated with 2% formalin. Four percent formaldehyde is a tuberculocidal agent, inactivating 104 M. tuberculosis in 2 minutes (73), and 2.5% formaldehyde inactivated about 107 S. typhi in 10 minutes in the presence of organic matter (485). Rubbo et al. (73) demonstrated that the sporicidal action of formaldehyde was slower than that of glutaraldehyde when they performed comparative tests with 4% aqueous formaldehyde and 2% glutaraldehyde against the spores of B. anthracis. The formaldehyde solution required a contact time of 2 hours to achieve an inactivation factor of 104, whereas glutaraldehyde required only 15 minutes. Uses Although formaldehyde-alcohol is a chemical sterilant and formaldehyde is a high-level disinfectant, the healthcare uses of formaldehyde are limited by its irritating fumes and the pungent odor that is apparent at very low levels (<1 ppm). For these reasons and others, such as it is also a suspected human carcinogen that is linked to nasal cancer and lung cancer (491), this germicide is excluded from Table 85.1. When it is employed there is generally limited direct employee exposure; however, excessive exposures to formaldehyde have been documented for employees of renal transplant units (487, 492) and students in a gross anatomy laboratory (493). Formaldehyde is used in the healthcare setting to prepare viral vaccines (e.g., poliovirus, influenza), as an embalming agent, to preserve anatomic specimens, and, in the past, for sterilizing surgical instruments, especially when mixed with ethanol. A 1997 survey found that formaldehyde was used for reprocessing hemodialyzers by 34% of the hemodialysis centers in the U.S., a 60% decrease from 1983 (494, 495). If used at room temperature, a concentration of 4% with a minimum exposure time of 24 hours is required to disinfect disposable hemodialyzers that are reused on the same patient (496, 497). Aqueous formaldehyde solutions (1–2%) also have been used to disinfect the internal fluid pathways of dialysis machines (497). To minimize a potential health hazard to dialysis patients, the dialysis equipment must be thoroughly rinsed and tested for residual formaldehyde before use. Paraformaldehyde, a solid polymer of formaldehyde, may be vaporized by heat for the gaseous decontamination of laminar flow biologic safety cabinets when maintenance work or filter changes require access to the sealed portion of the cabinet. Glutaraldehyde Overview Glutaraldehyde is a saturated dialdehyde that has gained wide acceptance as a high-level disinfectant and chemical sterilant (97). Aqueous solutions of glutaraldehyde are acidic and generally in this state are not sporicidal. Only when the solution is “activated” (made alkaline) by use of alkalinating agents to pH 7.5 to 8.5 does the solution become sporicidal. Once activated, these solutions have a shelf life of minimally 14 days because of the polymerization of the glutaraldehyde molecules at alkaline pH levels. This polymerization blocks the active sites (aldehyde groups) of the glutaraldehyde molecules that are responsible for its biocidal activity. Novel glutaraldehyde formulations (e.g., glutaraldehyde-phenol-sodium phenate, potentiated acid glutaraldehyde, stabilized alkaline glutaraldehyde) produced in the past 30 years have overcome the problem of rapid loss of activity (e.g., a use life of 28 to 30 days) while generally maintaining excellent microbicidal activity (498, 499, 500, 501, 502). However, it should be recognized that antimicrobial activity is dependent not only on age but also on use conditions such as dilution and organic stress. Manufacturers' literature for these preparations suggests that the neutral or alkaline glutaraldehydes possess superior microbicidal and anticorrosion properties when compared to acid glutaraldehydes, and a few published reports substantiate these claims (464, 503, 504). However, two studies found no difference in the microbicidal activity of alkaline and acid glutaraldehydes (64, 505). The use of glutaraldehyde-based solutions in healthcare facilities is widespread because of their advantages: excellent biocidal properties; P.1498 activity in the presence of organic matter (20% bovine serum); and noncorrosive action to endoscopic equipment, thermometers, rubber, or plastic equipment. The advantages, disadvantages, and characteristics of glutaraldehyde are listed in Tables 85.7 and 85.8. TABLE 85.7. COMPARISON OF THE CHARACTERISTICS OF SELECTED CHEMICALS USED PRIMARILY AS HIGH-LEVEL DISINFECTANTS TABLE 85.8. SUMMARY OF ADVANTAGES AND DISADVANTAGES OF CHEMICAL AGENTS USED AS CHEMICAL STERILANTS1 OR AS HIGH-LEVEL DISINFECTANTS Mode of Action The biocidal activity of glutaraldehyde is a consequence of its alkylation of sulfhydral, hydroxyl, carboxy, and amino groups of microorganisms, which alters RNA, DNA, and protein synthesis. Scott and Gorman (506, 507) provide an extensive review of the mechanism of action of glutaraldehydes. Microbicidal Activity The in vitro inactivation of microorganisms by glutaraldehydes has been extensively investigated and reviewed (506, 507). Several investigators showed that ≥2% aqueous solutions of glutaraldehyde, buffered to pH 7.5 to 8.5 with sodium bicarbonate, were effective in killing vegetative bacteria in less than 2 minutes; M. tuberculosis, fungi, and viruses in less than 10 minutes; and spores of Bacillus and Clostridium species in 3 hours (464, 506, 507, 508, 509, 510, 511). Spores of C. difficile are more rapidly killed by 2% glutaraldehyde than are spores of other species of Clostridium and Bacillus (70, 231, 232). There have been reports of microorganisms with significant resistance to glutaraldehyde, including some mycobacteria (M. chelonae, M. avium-intracellulare, M. xenopi) (512, 513, 514), Methylobacterium mesophilicum (515), Trichosporon, fungal ascospores (e.g., Microascus cinereus, Cheatomium globosum), and Cryptosporidium (279, 516). M. chelonae persisted in a 0.2% glutaraldehyde solution used to store porcine prosthetic heart valves (517). Collins and Montalbine (503) reported that 2% alkaline glutaraldehyde solution inactivated 105 M. tuberculosis cells present on the surface of penicylinders within 5 minutes at 18ВC. However, subsequent studies conducted by Rubbo et al. (73) questioned the mycobactericidal prowess of glutaraldehydes. They showed that 2% alkaline glutaraldehyde has slow action (20 to >30 minutes) against M. tuberculosis and compares unfavorably with alcohols, formaldehydes, iodine, and phenol. Collins (518) demonstrated that suspensions of Mycobacterium avium, M. intracellulare, and M. gordonae were more resistant to inactivation by a 2% alkaline glutaraldehyde (estimated time to complete inactivation, 60 minutes) than were virulent M. tuberculosis (estimated time to complete inactivation, 25 minutes). Collins (75) also showed that the rate of kill was directly proportional to the temperature and that sterility of a standardized suspension of M. tuberculosis could not be achieved within 10 minutes. A recently FDA-cleared chemical sterilant containing 2.5% glutaraldehyde uses increased temperature (35ВC) to reduce the time required to achieve high-level disinfection (5 minutes) (76), but its use P.1499 is limited to automatic endoscope reprocessors equipped with a heater. In another study employing membrane filters for measurement of mycobactericidal activity of 2% alkaline glutaraldehyde, Collins (72) demonstrated that complete inactivation was achieved within 20 minutes at 20ВC when the test inoculum was 106 M. tuberculosis per membrane. Several investigators have demonstrated that glutaraldehyde solutions inactivate 2.4 to >5.0 log10 of M. tuberculosis in 10 minutes (including multidrug-resistant M. tuberculosis) and 4.0 to 6.4 log10 of M. tuberculosis in 20 minutes (48, 50, 64, 67, 71, 72, 75, 518). On the basis of these data and other studies, 20 minutes at room temperature is the minimum exposure time needed to reliably kill Mycobacteria and other vegetative bacteria with a ≥2% glutaraldehyde (2, 15, 18, 23, 50, 74, 85, 99, 102, 103, 104, 105, 106). Dilution of glutaraldehyde during use commonly occurs, and studies show a glutaraldehyde concentration decline after a few days of use in an automatic endoscope washer (519, 520). This occurs because instruments are not thoroughly dried and water is carried in with the instrument, which increases the solution's volume and dilutes its effective concentration (521). This emphasizes P.1500 the need to ensure that semicritical equipment is disinfected with an acceptable concentration of glutaraldehyde. Data suggest that 1.0% to 1.5% glutaraldehyde is the minimum effective concentration for >2% glutaraldehyde solutions when used as a high-level disinfectant (67, 503, 504, 520). Chemical test strips or liquid chemical monitors (521, 522) are available for determining whether an effective concentration of glutaraldehyde is present despite repeated use and dilution. The frequency of testing should be based on how frequently the solutions are used (e.g., used daily, test daily; used weekly, test before use; used 30 times per day, test each tenth use), but the strips should not be used to extend the use life beyond the expiration date. Data suggest the chemicals in the test strip deteriorate with time (523) and a manufacturer's expiration date should be placed on the bottles. The bottle of test strips should be dated when opened and used for the period of time indicated on the bottle (e.g., 120 days). The results of test strip monitoring should be documented. The glutaraldehyde test kits have been preliminarily evaluated for accuracy and range (523), but the reliability has been questioned (524). The concentration should be considered unacceptable or unsafe when the test indicates a dilution below the product's minimum effective concentration (MEC) (generally to 1.0% to 1.5% glutaraldehyde or lower) by the indicator not changing color. A 2.0% glutaraldehyde–7.05% phenol–1.20% sodium phenate product that contained 0.125% glutaraldehyde–0.44% phenol–0.075% sodium phenate when diluted 1:16 was not recommended as a high-level disinfectant because of its lack of bactericidal activity in the presence of organic matter and its lack of tuberculocidal, fungicidal, virucidal, and sporicidal activity (43, 48, 49, 62, 64, 65, 66, 67, 68, 69, 70, 525). In December 1991, the EPA issued an order to stop the sale of all batches of this product based on efficacy data that showed that this product is not effective against spores and possibly other microorganisms or inanimate objects as claimed on the label (526). A new diluted glutaraldehyde containing 0.95% glutaraldehyde with 1.64% phenol/phenate has been cleared by the FDA as a high-level disinfectant. The other glutaraldehyde sterilants cleared by the FDA as of January 2002 contain 2.4% to 3.4% glutaraldehyde and are used undiluted (76). Uses Glutaraldehyde is used most commonly as a high-level disinfectant for medical equipment such as endoscopes (60, 97, 432), spirometry tubing, dialyzers (527), transducers, anesthesia and respiratory therapy equipment (528), hemodialysis proportioning and dialysate delivery systems (495, 529), and reuse of laparoscopic disposable plastic trocars (530). Glutaraldehyde is noncorrosive to metal and does not damage lensed instruments, rubber, or plastics. Glutaraldehyde should not be used for cleaning noncritical surfaces as it is too toxic and expensive. Colitis believed due to glutaraldehyde exposure from residual disinfecting solution in the endoscope solution channels has been reported and is preventable by careful endoscope rinsing (307, 531, 532, 533, 534, 535, 536, 537, 538, 539, 540, 541). One study found that residual glutaraldehyde levels were higher and more variable after manual disinfection (<0.2–159.5 mg/L) than after automatic disinfection (0.2–6.3 mg/L) (542). Similarly, keratopathy and corneal decompensation were caused by ophthalmic instruments that were inadequately rinsed after soaking in 2% glutaraldehyde (543, 544). Healthcare workers can become exposed to elevated levels of glutaraldehyde vapor when equipment is processed in poorly ventilated rooms, when spills occur, during activation or change-over of glutaraldehyde solutions (545), or when there are open immersion baths. Acute or chronic exposure may result in skin irritation or dermatitis, mucous membrane irritation (eye, nose, mouth), or pulmonary symptoms (307, 546, 547, 548, 549, 550). Epistaxis, allergic contact dermatitis, asthma, and rhinitis also have been reported in healthcare workers exposed to glutaraldehyde (547, 551, 552, 553, 554, 555, 556, 557, 558). Glutaraldehyde exposure should be monitored to ensure a safe work environment. Testing can be done by four techniques: a silica gel tube/gas chromatography with a flame ionization detector, dinitrophenylhydrazine (DNPH)-impregnated filter cassette/high-performance liquid chromatography (HPLC) with an ultraviolet (UV) detector, a passive badge/HPLC, or a hand-held glutaraldehyde air monitor (559). The silica gel tube and the DNPH-impregnated cassette are suitable for monitoring the 0.05-ppm ceiling limit. The passive badge, with a 0.02-ppm limit of detection, is considered marginal at the ACGIH ceiling level. The ceiling level is thought to be too close to the glutaraldehyde meter's 0.03-ppm limit of detection to provide confidence in the readings (559). ACGIH does not require a specific monitoring schedule for glutaraldehyde; however, a monitoring schedule is needed to ensure that the level is less than the ceiling limit. For example, monitoring should be done initially to determine glutaraldehyde levels, after procedural or equipment changes, and in response to worker complaints (560). In the absence of an OSHA PEL or NIOSH REL, if the glutaraldehyde level is higher than the ACGIH ceiling limit of 0.05 ppm, it would be prudent to take corrective action and repeat monitoring (560). Engineering and work practice controls that may be used to combat these problems include ducted exhaust hoods, air systems that provide 7 to 15 air exchanges per hour, ductless fume hoods with absorbents for the glutaraldehyde vapor, tight-fitting lids on immersion baths, personal protection (e.g., nitrile or butyl rubber gloves but not natural latex gloves; goggles) to minimize skin or mucous membrane contact, and automated endoscope processors (7, 561). If engineering controls fail to maintain levels below the ACGIH, institutions may consider the use of respirators [e.g., a half-face respirator with organic vapor cartridge (551) or a type C supplied air respirator with a full face piece operated in a positive pressure mode (562)]. In general, engineering controls are preferred over work practice and administrative controls, as they do not require the active participation of the healthcare worker. Even though enforcement of the OSHA ceiling limit was suspended in 1993 by the U.S. Court of Appeals (490), it is prudent to limit employee exposure to 0.05 ppm (per ACGIH) since at this level glutaraldehyde is irritating to the eyes, throat, and nose (307, 490, 550, 563). If glutaraldehyde disposal via the sanitary sewer system is restricted, sodium bisulfate can be used to neutralize the glutaraldehyde and make it safe for disposal. P.1501 Hydrogen Peroxide Overview The literature contains several accounts of the properties, germicidal effectiveness, and potential uses for stabilized hydrogen peroxide in the healthcare setting. Published reports ascribe good germicidal activity to hydrogen peroxide and attest to its bactericidal, virucidal, sporicidal, and fungicidal properties (564, 565, 566). The advantages, disadvantages, and characteristics of hydrogen peroxide are listed in Tables 85.7 and 85.8. Mode of Action Hydrogen peroxide works by the production of destructive hydroxyl free radicals that can attack membrane lipids, DNA, and other essential cell components. Catalase, produced by aerobic and facultative anaerobes that possess cytochrome systems, may protect cells from metabolically produced hydrogen peroxide by degrading hydrogen peroxide to water and oxygen. This defense is overwhelmed by the concentrations used for disinfection (564, 565). Microbicidal Activity Hydrogen peroxide is active against a wide range of microorganisms, including bacteria, yeasts, fungi, viruses, and spores (69, 565). Schaeffer et al. (567) demonstrated the bactericidal effectiveness and stability of hydrogen peroxide in urine against a variety of healthcare-associated pathogens. They showed that microorganisms with high cellular catalase activity (e.g., S. aureus, S. marcescens, and Proteus mirabilis) required 30 to 60 minutes of exposure to 0.6% hydrogen peroxide for a 108 reduction in cell counts, whereas microorganisms with lower catalase activity (e.g., E. coli, Streptococcus species, and Pseudomonas species) required only 15 minutes exposure. Wardle and Renninger (568) investigated 3%, 10%, and 15% hydrogen peroxide for reducing spacecraft bacterial populations and got a complete kill of 106 spores (i.e., Bacillus species) with a 10% concentration and a 60-minute exposure time. A 3% concentration for 150 minutes killed 106 spores in six of seven exposure trials (568). Sagripanti and Bonifacino (569, 570) found that a 10% hydrogen peroxide solution resulted in a 103 decrease in B. atrophaeus spores and a 105 or greater decrease when tested against 13 other pathogens in 30 minutes at 20ВC. A 3.0% hydrogen peroxide solution was ineffective against VRE after 3- and 10-minute exposure times (571) and caused only a 2-log10 reduction in the number of Acanthamoeba cysts in approximately 2 hours (572). A 7% stabilized hydrogen peroxide proved to be sporicidal (6 hours exposure time), mycobactericidal (20 minutes), and fungicidal (5 minutes) at full strength, and virucidal (5 minutes) and bactericidal (3 minutes) at a 1:16 dilution when using a quantitative carrier test (566). The 7% solution of hydrogen peroxide, tested after 14 days of stress (in the form of germ-loaded carriers and respiratory therapy equipment), was found to be sporicidal (>7 log10 reduction in 6 hours), mycobactericidal (>6.5 log10 reduction in 25 minutes), fungicidal (>5 log10 reduction in 20 minutes), bactericidal (>6 log10 reduction in 5 minutes), and virucidal (5 log10 reduction in 5 minutes) (573). Synergistic sporicidal effects were observed when spores were exposed to a combination of hydrogen peroxide (5.9% to 23.6%) and peracetic acid (574). The antiviral activity of hydrogen peroxide against rhinovirus was demonstrated in studies by Mentel and Schmidt (575). The time required for inactivating three serotypes of rhinovirus using a 3% hydrogen peroxide solution was 6 to 8 minutes; this time increased with decreasing concentrations (18–20 minutes at 1.5%, 50–60 minutes at 0.75%). Concentrations of hydrogen peroxide from 6% to 25% have promise as chemical sterilants. The product marketed as a sterilant is a premixed, ready-to-use chemical that contains 7.5% hydrogen peroxide and 0.85% phosphoric acid (to maintain a low pH) (60). The mycobactericidal activity of 7.5% hydrogen peroxide has been corroborated by Sattar (576), who showed the inactivation of >105 multidrug resistant M. tuberculosis after a 10-minute exposure (576). Thirty minutes were required for >99.9% inactivation of polio and hepatitis A viruses (577). Mbithi et al. (51) showed that 3% and 6% hydrogen peroxide were unable to inactivate the hepatitis A virus in 1 minute using a carrier test. The effectiveness of 7.5% hydrogen peroxide at 10 minutes was compared to 2% alkaline glutaraldehyde at 20 minutes in manual disinfection of endoscopes; no significant difference in germicidal activity was observed (578). There also were no complaints received from the nursing or medical staff in terms of odor or toxicity. In one study, 6% hydrogen peroxide (unused product was 7.5%) was more effective in the high-level disinfection of flexible endoscopes than was the 2% glutaraldehyde solution (579). A new, rapid-acting 13.4% hydrogen peroxide formulation (currently not FDA-cleared) has demonstrated sporicidal, mycobactericidal, fungicidal, and virucidal efficacy. Manufacturer's data demonstrate that this solution sterilizes in 30 minutes and provides high-level disinfection in 5 minutes (580). This product has not been used long enough to evaluate material compatibility to endoscopes and other semicritical devices, and further assessment by instrument manufacturers should be done. Under normal conditions, hydrogen peroxide is extremely stable when properly stored (e.g., in dark containers). The decomposition or loss of potency in small containers is less than 2% per year at ambient temperatures (581). Uses Commercially available 3% hydrogen peroxide is a stable and effective disinfectant when used on inanimate surfaces. It has been used in concentrations from 3% to 6% for the disinfection of soft contact lenses (e.g., 3% for 2 to 3 hours) (564, 582, 583), tonometer biprisms (440), ventilators (584), fabrics (371), and endoscopes (579). Hydrogen peroxide was effective in spot-disinfecting fabrics in patients' rooms (371). Corneal damage from a hydrogen peroxide–soaked tonometer tip that was not properly rinsed has been reported (585). Hydrogen peroxide also has been instilled into urinary drainage bags in an attempt to eliminate the bag as a source of bladder bacteriuria and environmental contamination (586). Although the instillation of hydrogen peroxide into the bag reduced microbial contamination of the bag, this procedure did not reduce the incidence of catheter-associated bacteriuria (586). P.1502 A chemical irritation resembling pseudomembranous colitis, which was caused by either 3% hydrogen peroxide or a 2% glutaraldehyde, has been reported (532). An epidemic of pseudomembrane-like enteritis and colitis in seven patients in a gastrointestinal endoscopy unit also has been associated with inadequate rinsing of 3% hydrogen peroxide from the endoscope (587). As with other chemical sterilants, dilution of the hydrogen peroxide must be monitored by regularly testing the minimum effective concentration (i.e., 7.5% to 6.0%). Compatibility testing by Olympus America of the 7.5% hydrogen peroxide found both cosmetic changes (e.g., discoloration of black anodized metal finishes) (60) and functional changes with the tested endoscopes (Olympus, written communication, October 15, 1999). Iodophors Overview Iodine solutions or tinctures have long been used by health professionals, primarily as antiseptics on skin or tissue. Iodophors, on the other hand, have been used both as antiseptics and disinfectants. An iodophor is a combination of iodine and a solubilizing agent or carrier; the resulting complex provides a sustained-release reservoir of iodine and releases small amounts of free iodine in aqueous solution. The best-known and most widely used iodophor is povidone-iodine, a compound of polyvinylpyrrolidone with iodine. This product and other iodophors retain the germicidal efficacy of iodine but unlike iodine are generally nonstaining and are relatively free of toxicity and irritancy (588, 589). Several reports that documented intrinsic microbial contamination of antiseptic formulations of povidone-iodine and poloxamer-iodine (590, 591, 592) caused a reappraisal of the chemistry and use of iodophors (593). It was found that “free” iodine (I2) contributes to the bactericidal activity of iodophors, and dilutions of iodophors demonstrate more rapid bactericidal action than does a full-strength povidone-iodine solution. The reason for the observation that dilution increases bactericidal activity is unclear but it has been suggested that dilution of povidone-iodine results in weakening of the iodine linkage to the carrier polymer with an accompanying increase of free iodine in solution (591). Therefore, iodophors must be diluted according to the manufacturers' directions to achieve antimicrobial activity. Mode of Action Iodine is able to penetrate the cell wall of microorganisms quickly and it is thought that the lethal effects result from a disruption of protein and nucleic acid structure and synthesis. Microbicidal Activity Published reports on the in vitro antimicrobial efficacy of iodophors demonstrate that iodophors are bactericidal, mycobactericidal, and virucidal but may require prolonged contact times to kill certain fungi and bacterial spores (12, 62, 63, 64, 297, 594, 595, 596, 597). Berkelman et al. (594) found that three brands of povidone-iodine solution demonstrated more rapid kill (seconds to minutes) of S. aureus and M. chelonae at a 1:100 dilution than did the stock solution. Klein and DeForest (63) demonstrated the virucidal activity of 75 to 150 ppm available iodine against seven viruses. Other investigators have questioned the efficacy of iodophors against poliovirus in the presence of organic matter (596) and rotavirus SA-11 in distilled or tap water (297). Manufacturers' data demonstrate that commercial iodophors are not sporicidal, but they are tuberculocidal, fungicidal, virucidal, and bactericidal at their recommended use-dilution. Uses Besides their use as an antiseptic, iodophors have been used for the disinfection of blood culture bottles and medical equipment such as hydrotherapy tanks, thermometers, and, in the past, endoscopes. Antiseptic iodophors are not suitable for use as hard-surface disinfectants because of concentration differences. Iodophors formulated as antiseptics contain less free iodine than those formulated as disinfectants (355). Iodine or iodine-based antiseptics should not be used on silicone catheters as the silicone tubing may be adversely affected (598). Ortho-phthalaldehyde (OPA) Overview OPA is a high-level disinfectant that received FDA clearance in October 1999. It contains 0.55% 1,2-benzenedicarboxaldehyde or OPA. OPA solution is a clear, pale-blue liquid with a pH of 7.5. The advantages, disadvantages, and characteristics of OPA are listed in Tables 85.7 and 85.8. Mode of Action Preliminary studies on the mode of action of OPA suggest that both OPA and glutaraldehyde interact with amino acids, proteins, and microorganisms. However, OPA is a less potent cross-linking agent. This is compensated for by the lipophilic aromatic nature of OPA that is likely to assist its uptake through the outer layers of mycobacteria and gram-negative bacteria (599, 600). OPA appears to kill spores by blocking the spore germination process (601). Microbicidal Activity Studies have demonstrated excellent microbicidal activity in in vitro studies (60, 91, 279, 374, 602, 603, 604, 605, 606, 607, 608, 609, 610, 611). For example, Gregory et al. (603) demonstrated that OPA has superior mycobactericidal activity (5-log10 reduction in 5 minutes) compared to glutaraldehyde. The mean times required to produce a 6-log10 reduction for M. bovis using 0.21% OPA was 6 minutes compared to 32 minutes using 1.5% glutaraldehyde. OPA showed good activity against the mycobacteria tested, including the glutaraldehyde-resistant strains, but 0.5% OPA was not sporicidal with 270 minutes of exposure. Increasing the pH from its unadjusted level (about 6.5) to pH 8 improved the sporicidal activity P.1503 of OPA (604). Chan-Myers and Roberts (607) showed that the level of biocidal activity was directly related to the temperature. A greater than 5-log10 reduction of B. atrophaeus spores was observed in 3 hours at 35ВC as compared to 24 hours at 20ВC. Also, with an exposure time at or below 5 minutes, a decrease in biocidal activity was observed with increasing serum concentration. However, there was no difference in efficacy when the exposure time was 10 minutes or longer. Walsh et al. (604) also found OPA effective (>5-log10 reduction) against a wide range of microorganisms, including glutaraldehyde-resistant mycobacteria and B. atrophaeus spores. Uses OPA has several potential advantages compared to glutaraldehyde. It has excellent stability over a wide pH range (pH 3–9), is not a known irritant to the eyes and nasal passages, does not require exposure monitoring, has a barely perceptible odor, and requires no activation. OPA, like glutaraldehyde, has excellent material compatibility. A potential disadvantage of OPA is that it stains proteins gray (including unprotected skin) and thus must be handled with caution (60). However, skin staining would indicate improper handling that requires additional training or PPE (gloves, eye and mouth protection, fluid-resistant gowns). PPE should be worn when handling contaminated instruments, equipment, and chemicals (374). In addition, equipment must be thoroughly rinsed to prevent discoloration of a patient's skin or mucous membranes. Since OPA was only recently cleared for use as a highlevel disinfectant, only limited clinical studies are available. In a clinical-use study, exposure of 100 endoscopes for 5 minutes to OPA resulted in a >5-log10 reduction in bacterial load. Further, OPA was effective over a 14-day usage cycle (91). Manufacturer's data show that OPA lasts longer in an automatic endoscope reprocessor before reaching its MEC limit (MEC after 82 cycles) compared to glutaraldehyde (MEC after 40 cycles) (374). Disposal must be done in accordance with local and state regulations. If OPA disposal via the sanitary sewer system is restricted, glycine (25 g/gallon) can be used to neutralize the OPA and make it safe for disposal. The high-level disinfectant label claims for OPA solution at 20ВC vary worldwide, e.g., 5 minutes in Europe, Asia, and Latin America; 10 minutes in Canada and Australia; and 12 minutes in the U.S. These label claims are different worldwide because of differences in the test methodology and requirements for licensure. Peracetic Acid Overview Peracetic, or peroxyacetic, acid is characterized by a very rapid action against all microorganisms. Special advantages of peracetic acid are that it lacks harmful decomposition products (i.e., acetic acid, water, oxygen, hydrogen peroxide), it enhances removal of organic material (612), and leaves no residue. It remains effective in the presence of organic matter and is sporicidal even at low temperatures. Peracetic acid can corrode copper, brass, bronze, plain steel, and galvanized iron, but these effects can be reduced by additives and pH modifications. It is considered unstable, particularly when diluted; for example, a 1% solution loses half its strength through hydrolysis in 6 days, whereas 40% peracetic acid loses 1% to 2% of its active ingredients per month (565). The advantages, disadvantages, and characteristics of peracetic acid are listed in Tables 85.7 and 85.8. Mode of Action Little is known about the mechanism of action of peracetic acid, but it is thought to function similarly to other oxidizing agents; that is, it denatures proteins, disrupts the cell wall permeability, and oxidizes sulfhydral and sulfur bonds in proteins, enzymes, and other metabolites (565). Microbicidal Activity Peracetic acid inactivates gram-positive and gram-negative bacteria, fungi, and yeasts in в‰5 minutes at <100 ppm. In the presence of organic matter, 200 to 500 ppm is required. For viruses, the dosage range is wide (12–2,250 ppm), with poliovirus inactivated in yeast extract in 15 minutes with 1,500 to 2,250 ppm. One study showed that 3.5% peracetic acid was ineffective against the hepatitis A virus after 1-minute exposure using a carrier test (51). With bacterial spores, 500 to 10,000 ppm (0.05% to 1%) inactivates spores in 15 seconds to 30 minutes using a spore suspension test (565, 569, 613, 614). Uses An automated machine using peracetic acid to chemically sterilize medical (e.g., endoscopes, arthroscopes), surgical, and dental instruments is used in the U.S. (615, 616, 617). As previously noted, dental handpieces should be steam sterilized. The sterilant, 35% peracetic acid, is diluted to 0.2% with filtered water at a temperature of 50ВC. Simulated-use trials have demonstrated excellent microbicidal activity (99, 617, 618, 619, 620, 621), and three clinical trials have demonstrated both excellent microbial killing and no clinical failures leading to infection (81, 622, 623). The high efficacy of the system was demonstrated by Alfa et al. (621), who compared the efficacies of the system with that of ETO. Only the peracetic acid system was able to kill 6 log10 of M. chelonae, Enterococcus faecalis, and B. atrophaeus spores with both an organic and inorganic challenge. An investigation by Fuselier and Mason (81) compared the costs, performance, and maintenance of urologic endoscopic equipment processed by high-level disinfection (with glutaraldehyde) with those of the peracetic acid system and reported no clinical differences between the two systems. However, the use of this system led to increased costs when compared to high-level disinfection, including costs for processing ($6.11 vs. $0.45 per cycle), purchasing and training ($24,845 vs. $16), installation ($5,800 vs. $0), and endoscope repairs ($6,037 vs. $445) (81). Further, three clusters of infection using the peracetic acid automated endoscope reprocessor were linked to inadequately processed bronchoscopes when inappropriate channel connectors were used with the system (624). P.1504 These clusters highlight the importance of training, proper model-specific endoscope connector systems, and quality control procedures to ensure compliance with endoscope manufacturer's recommendations and professional organization guidelines. An alternative high-level disinfectant available in the U.K. contains 0.35% peracetic acid. Although this product is rapidly effective against a broad range of microorganisms (625, 626, 627), it tarnishes the metal of endoscopes and is unstable, resulting in only a 24-hour use life (627). Peracetic Acid and Hydrogen Peroxide Overview Two chemical sterilants are available that contain peracetic acid plus hydrogen peroxide [0.08% peracetic acid plus 1.0% hydrogen peroxide (no longer marketed), 0.23% peracetic acid plus 7.35% hydrogen peroxide]. The advantages, disadvantages, and characteristics of peracetic acid and hydrogen peroxide are listed in Tables 85.7 and 85.8. Microbicidal Activity The bactericidal properties of peracetic acid and hydrogen peroxide have been demonstrated (628). Manufacturer's data demonstrated that this inactivated all microorganisms with the combination of peracetic acid and hydrogen peroxide with the exception of bacterial spores within 20 minutes. The 0.08% peracetic acid plus 1.0% hydrogen peroxide product was effective in inactivating a glutaraldehyde-resistant mycobacterium (629). Uses The combination of peracetic acid and hydrogen peroxide has been used for disinfecting hemodialyzers (630). The percentage of dialysis centers using a peracetic acid–hydrogen peroxide–based disinfectant for reprocessing dialyzers increased from 5% in 1983 to 56% in 1997 (495). Olympus America (written communication, April 15, 1998) does not endorse the use of 0.08% peracetic acid plus 1.0% hydrogen peroxide on any Olympus endoscope due to cosmetic and functional damage, and will not assume liability for chemical damage as a result of the use of this product. This product is not currently available. A newer chemical sterilant with 0.23% peracetic acid and 7.35% hydrogen peroxide has been cleared by the FDA, and its characteristics, advantages, and disadvantages are shown in Tables 85.7 and 85.8. Olympus America (written communication, September 13, 2000) tested the 7.35% hydrogen peroxide and 0.23% peracetic acid product and concluded it was not compatible with its flexible gastrointestinal endoscopes based on immersion studies where the test insertion tubes had failed due to swelling and loosening of the black polymer layer of the tube. Phenolics Overview Phenol has occupied a prominent place in the field of hospital disinfection since its initial use as a germicide by Lister in his pioneering work on antiseptic surgery. In the past 30 years, however, work has been concentrated on the numerous phenol derivatives or phenolics and their antimicrobial properties. Phenol derivatives originate when a functional group (e.g., alkyl, phenyl, benzyl, halogen) replaces one of the hydrogen atoms on the aromatic ring. Two phenol derivatives commonly found as constituents of hospital disinfectants are ortho-phenylphenol and ortho-benzyl-para-chlorophenol. The antimicrobial properties of these compounds and many other phenol derivatives are much improved over those of the parent chemical. Phenolics are absorbed by porous materials and the residual disinfectant may cause tissue irritation. In 1970 Kahn (631) reported that depigmentation of the skin is caused by phenolic germicidal detergents containing para-tertiary butylphenol and para-tertiary amylphenol. Mode of Action Phenol, in high concentrations, acts as a gross protoplasmic poison, penetrating and disrupting the cell wall and precipitating the cell proteins. Low concentrations of phenol and higher molecular-weight phenol derivatives cause bacterial death by the inactivation of essential enzyme systems and leakage of essential metabolites from the cell wall (632). Microbicidal Activity Published reports on the antimicrobial efficacy of commonly used phenolics showed that they were bactericidal, fungicidal, virucidal, and tuberculocidal (12, 54, 62, 64, 206, 387, 486, 632, 633, 634, 635, 636, 637, 638). One study demonstrated little or no virucidal effect of a phenolic against coxsackie B4, echovirus 11, and poliovirus 1 (636). Similarly, Klein and DeForest (63) observed that 12% ortho-phenylphenol failed to inactivate any of the three hydrophilic viruses after a 10-minute exposure time, although 5% phenol was lethal for these viruses. A 0.5% dilution of a phenolic (2.8% ortho-phenylphenol and 2.7% ortho-benzyl-para-chlorophenol) inactivated HIV (206), and a 2% solution of a phenolic (15% ortho-phenylphenol and 6.3% para-tertiary-amylphenol) inactivated all but one of 11 fungi tested (62). Manufacturers' data using the standardized AOAC methods demonstrate that commercial phenolics are not sporicidal but are tuberculocidal, fungicidal, virucidal, and bactericidal at their recommended use-dilution. Attempts to substantiate the bactericidal label claims of phenolics using the AOAC use-dilution method have failed on occasion (387, 637). However, these same studies have shown extreme variability of test results among laboratories testing identical products. Uses Many phenolic germicides are EPA-registered as disinfectants for use on environmental surfaces (e.g., bedside tables, bed rails, laboratory surfaces) and noncritical medical devices. Phenolics are not FDA-cleared as high-level disinfectants for use with semicritical items but could be used to preclean or decontaminate critical and semicritical devices prior to terminal sterilization or high-level disinfection. P.1505 The use of phenolics in nurseries has been questioned because of the occurrence of hyperbilirubinemia in infants placed in bassinets where phenolic detergents were used (639). In addition, Doan et al. (640) demonstrated bilirubin level increases in phenolic-exposed infants compared to nonphenolic-exposed infants when the phenolic was prepared according to the manufacturers' recommended dilution. If phenolics are used to clean nursery floors, they must be diluted according to the recommendation on the product label. Phenolics (and other disinfectants) should not be used to clean infant bassinets and incubators while occupied. If phenolics are used to terminally clean infant bassinets and incubators, the surfaces should be rinsed thoroughly with water and dried before the infant bassinets and incubators are reused (15). Quaternary Ammonium Compounds Overview The quaternary ammonium compounds are widely used as disinfectants. There have been some reports of healthcare-associated infections associated with contaminated quaternary ammonium compounds used to disinfect patient-care supplies or equipment such as cystoscopes or cardiac catheters (641, 642). The quaternary ammonium compounds are good cleaning agents, but high water hardness (643) and materials such as cotton and gauze pads may make them less microbicidal because of insoluble precipitates and because cotton and gauze pads absorb the active ingredients. As with several other disinfectants (e.g., phenolics, iodophors) gram-negative bacteria have been found to survive or grow in them (378). Chemically, the quaternaries are organically substituted ammonium compounds in which the nitrogen atom has a valence of 5, four of the substituent radicals (R1–R4) are alkyl or heterocyclic radicals of a given size or chain length, and the fifth (X-) is a halide, sulfate, or similar radical (644). Each compound exhibits its own antimicrobial characteristics, hence the search for one compound with outstanding antimicrobial properties. Some of the chemical names of quaternary ammonium compounds used in healthcare are alkyl dimethyl benzyl ammonium chloride, alkyl didecyl dimethyl ammonium chloride, and dialkyl dimethyl ammonium chloride. The newer quaternary ammonium compounds (i.e., fourth generation), referred to as twin-chain or dialkyl quaternaries (e.g., didecyl dimethyl ammonium bromide and dioctyl dimethyl ammonium bromide), purportedly remain active in hard water and are tolerant of anionic residues (645). A few case reports have documented occupational asthma as a result of exposure to benzalkonium chloride (646). Mode of Action The bactericidal action of the quaternaries has been attributed to the inactivation of energy-producing enzymes, denaturation of essential cell proteins, and disruption of the cell membrane (645). Evidence in support of these and other possibilities is provided by Sykes (644) and Petrocci (647). Microbicidal Activity Results from manufacturers' data sheets and from published scientific literature indicate that the quaternary ammonium compounds sold as hospital disinfectants are generally fungicidal, bactericidal, and virucidal against lipophilic (enveloped) viruses; they are not sporicidal and generally not tuberculocidal or virucidal against hydrophilic (nonenveloped) viruses (12, 47, 48, 49, 51, 52, 54, 62, 64, 300, 647, 648, 649). Best et al. (48) and Rutala et al. (64) demonstrated the poor mycobactericidal activities of quaternary ammonium compounds. Attempts to reproduce the manufacturers' bactericidal and tuberculocidal claims using the AOAC tests with a limited number of quaternary ammonium compounds have failed on occasion (64, 387, 637). Studies have shown, however, extreme variability of test results among laboratories testing identical products (387, 637). Uses The quaternary ammonium compounds are commonly used in ordinary environmental sanitation of noncritical surfaces such as floors, furniture, and walls. EPA-registered quaternary ammonium compounds are appropriate to use when disinfecting medical equipment that comes into contact with intact skin (e.g., blood pressure cuffs). Miscellaneous Inactivating Agents Other Germicides Several compounds have antimicrobial activity but for various reasons have not been incorporated into our armamentarium of healthcare disinfectants. These include mercurials, sodium hydroxide, ОІ-propiolactone, chlorhexidine gluconate, cetrimide-chlorhexidine, glycols (triethylene and propylene), and the Tego disinfectants. A detailed examination of these agents is presented in two authoritative references (14, 384). A peroxygen-containing formulation had marked bactericidal action when used as a 1% weight/volume solution and virucidal activity at 3% (43) but did not have mycobactericidal activity at concentrations of 2.3% and 4% and exposure times ranging between 30 and 120 minutes (650). It also required 20 hours to kill B. atrophaeus spores (651). A powder-based peroxygen compound for disinfecting contaminated spill was strongly and rapidly bactericidal (652). Metals such as silver, iron, and copper could be used for the disinfection of water, reusable medical devices, or incorporated into medical devices (e.g., intravascular catheters) (653, 654, 655, 656, 657, 658). Preliminary data suggest they are effective against a wide variety of microorganisms. Nanoemulsions, composed of detergents and lipids in water, have been shown in preliminary studies to have activity against vegetative bacteria, enveloped viruses, Bacillus spores, and Candida. This product represents a potential agent for use as a topical biocidal agent (659, 660, 661). “Superoxidized Water” Reports have examined the microbicidal activity of a new disinfectant, “superoxidized water.” The concept of electrolyzing P.1506 saline to create a disinfectant or antiseptics is appealing as the basic materials of saline and electricity are cheap and the end product (i.e., water) is not damaging to the environment. The main products of this water are hypochlorous acid at a concentration of about 144 mg/L and chlorine. As with any germicide, the antimicrobial activity of superoxidized water is strongly affected by the concentration of the active ingredient (available free chlorine) (662). The disinfectant is generated at the point of use by passing a saline solution over coated titanium electrodes at 9 amps. The product generated has a pH of 5.0 to 6.5 and an oxidation-reduction potential (redox) of >950 mV. Although “superoxidized water” is intended to be generated fresh at the point of use, when tested under clean conditions the disinfectant is effective within 5 minutes when 48 hours old (663). Unfortunately, the equipment required to produce the product may be expensive as parameters such as pH, current, and redox potential must be closely monitored. The solution has been shown to be nontoxic to biologic tissues. Although the solution is claimed by the manufacturer in the U.K. to be noncorrosive and nondamaging to endoscopes and processing equipment, one flexible endoscope manufacturer (Olympus Key-Med, U.K.) has voided the warranty on the endoscopes if superoxidized water is used to disinfect them (664). The antimicrobial activity of this new, recently FDA-cleared (FDA correspondence, September 18, 2002) high-level disinfectant has been tested against bacteria, mycobacteria, viruses, fungi, and spores (663, 665, 666). Data have shown that freshly generated superoxidized water is rapidly effective (<2 minutes) in achieving a 5-log10 reduction of pathogenic microorganisms (e.g., M. tuberculosis, M. chelonae, poliovirus, HIV, MRSA, E. coli, Candida albicans, Enterococcus faecalis, P. aeruginosa) in the absence of organic loading. However, the biocidal activity of this disinfectant was substantially reduced in the presence of organic material (5% horse serum) (663, 666). No bacteria or viruses were detected on artificially contaminated endoscopes after 5 minutes exposure to superoxidized water (667). Additional studies are needed to determine if this solution may be used as an alternative to other disinfectants or antiseptics for handwashing, skin antisepsis, room cleaning, or equipment disinfection (e.g., endoscopes, dialyzers) (374, 665, 668). Metals as Microbicides Comprehensive reviews of antisepsis (669), disinfection (391), and antiinfective chemotherapy (670) barely mention the antimicrobial activity of heavy metals (657, 658). Nevertheless, it has been known since antiquity that some heavy metals possess antiinfective activity. Heavy metals such as silver have been used for prophylaxis of conjunctivitis of the newborn, topical therapy for burn wounds, and bonding to indwelling catheters, and the use of heavy metals as antiseptics or disinfectants is also being reexplored. Clinical uses of other heavy metals include the use of copper-8-quinolinolate as a fungicide against Aspergillus, copper-silver ionization for Legionella disinfection (671, 672, 673), the use of organic mercurials as an antiseptic (e.g., mercurochrome) and preservative/disinfectant (e.g., thimerosal—currently being removed from vaccines) in pharmaceuticals and cosmetics (658). Ultraviolet (UV) Radiation UV has a wavelength range between 328 and 210 nm (3,280 and 2,100 ГҐ). Its maximum bactericidal effect occurs at 240 to 280 nm. Mercury vapor lamps emit more than 90% of their radiation at 253.7 nm, which is near the maximum microbicidal activity (674). Inactivation of microorganisms is due to destruction of nucleic acid via induction of thymine dimers. UV has been employed in the disinfection of drinking water, air (674), titanium implants (675), and contact lenses (676). Studies have shown that bacteria and viruses are more easily killed by UV light than are bacterial spores (674). UV has several potential applications. but unfortunately its germicidal effectiveness and use is influenced by the following factors: organic matter; wavelength; type of suspension; temperature; type of microorganism; and UV intensity, which is affected by distance and dirty tubes (677). The application of UV in the healthcare environment (i.e., operating rooms, isolation rooms, and biologic safety cabinets) is limited to the destruction of airborne microorganisms or inactivation of microorganisms located on surfaces. The effect of UV radiation on postoperative wound infections has been investigated by means of a double-blind, randomized study in five university medical centers. After following 14,854 patients over a 2-year period, the investigators reported the overall wound infection rate to be unaffected by UV, although there was a significant reduction (3.8% to 2.9%) in postoperative infection in the “refined clean” surgical procedures (678). No data support the use of UV lamps in isolation rooms, and this practice has caused at least one epidemic of UV-induced skin erythema and keratoconjunctivitis in hospital patients and visitors (679). Pasteurization Pasteurization is not a sterilization process; its purpose is to destroy all pathogenic microorganisms with the exception of bacterial spores. The time-temperature relation for hot-water pasteurization is generally >70ВC (158ВF) for 30 minutes. The water temperature should be monitored as part of a quality assurance program (680). Pasteurization of respiratory therapy (681, 682) and anesthesia equipment (683) is a recognized alternative to chemical disinfection. The efficacy of this process has been tested using an inoculum that the authors believed might simulate contamination by an infected patient. Using a large inoculum (107) of P. aeruginosa or A. calcoaceticus in sets of respiratory tubing before processing, Gurevich et al. (681) demonstrated that machine-assisted chemical processing was more efficient than machine-assisted pasteurization with a disinfection failure rate of 6% and 83%, respectively. Other investigators found hot water disinfection to be effective (inactivation factor >5 log10) for the disinfection of reusable anesthesia or respiratory therapy equipment (682, 683). Flushing and Washer Disinfectors Flushing and washer disinfectors are automated and closed equipment that clean and disinfect objects from bedpans and washbowls to surgical instruments and anesthesia tubes. Items P.1507 such as bedpans and urinals can be cleaned and disinfected in flushing disinfectors. They have a short cycle of a few minutes. They clean by flushing with warm water, possibly with a detergent, and then disinfect by flushing the items with hot water at approximately 90ВC for 1 minute, or with steam. Since this machine empties, cleans, and disinfects, manual cleaning is eliminated, fewer disposable items are needed, and less chemical germicides are used. A microbiologic evaluation of one washer/disinfector demonstrated that suspensions of Enterococcus faecalis or poliovirus were completely inactivated (684). Other studies have shown that strains of Enterococcus faecium are able to survive the British standard for heat disinfection of bedpans (80ВC for 1 minute). The significance of this finding with reference to the potential for enterococci to survive and disseminate in the healthcare environment is debatable (685, 686, 687). These machines are available and used in many European countries. Surgical instruments and anesthesia equipment, which are more difficult to clean, are run in washer disinfectors with a longer cycle of some 20 to 30 minutes with the use of a detergent. These machines also disinfect by hot water at approximately 90ВC (688). Registration and Neutralization of Germicides Any discussion of germicidal efficacy would be incomplete without commenting on the evaluation and registration of germicides to assure that they meet manufacturers' label claims. Chemical germicides formulated as disinfectants or chemical sterilants in the U.S. are registered and regulated in interstate commerce by the Antimicrobial Division, Office of Pesticides Program, EPA. The authority for this activity was mandated by the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) of 1947. In the past, the EPA required manufacturers of chemical germicides formulated as sanitizers, disinfectants, or chemical sterilants to test formulations by using accepted methods for microbicidal activity, stability, and toxicity to animals and humans. In June 1993, the FDA and EPA issued a memorandum of understanding that divided responsibility for review and surveillance of chemical germicides between the two agencies. Under the agreement, the FDA regulates chemical sterilants used on critical and semicritical devices, and the EPA regulates disinfectants used on noncritical surfaces (689). In 1996, Congress passed the Food Quality Protection Act (FQPA), which amended FIFRA in regard to several products regulated by both the EPA and FDA. One provision of FQPA is that regulation of liquid chemical sterilants used on critical and semicritical medical devices (EPA continues to register nonmedical chemical sterilants) was removed from the jurisdiction of EPA and now rests solely with the FDA (690). The FDA and EPA have considered the impact of FQPA, and the FDA has published its final guidance document on production submissions and labeling, January 2000. The methods that EPA has used for registration are standardized by the AOAC; however, a survey of the scientific literature indicates numerous deficiencies associated with these tests (51, 67, 71, 396, 636, 637, 691, 692, 693, 694, 695, 696) that cause them to be neither accurate nor reproducible (387, 637). As part of their regulatory authority, the EPA and FDA support the development and validation of methods for assessing disinfection claims (697, 698). For example, the EPA has supported the work of Sattar and Springthorpe (611), who have developed a two-tier quantitative carrier test that can be used to assess sporicidal, mycobactericidal, bactericidal, fungicidal, virucidal, and protozoacidal activity of chemical germicides. The EPA is accepting label claims against HBV using the duck hepatitis B model to quantify disinfectant activity (109, 699). The EPA also may do the same for HCV using the bovine viral diarrhea virus as a surrogate. Antiseptics are considered to be antimicrobial drugs used on living tissue and thus are regulated by the FDA under the Food, Drug, and Cosmetic Act. The FDA regulates liquid chemical sterilants/high-level disinfectants intended to process critical and semicritical devices. The FDA has published recommendations on the types of test methods that manufactures should submit to the FDA for 510[k] clearance for such agents. For nearly 30 years, the EPA also performed intramural pre- and postregistration efficacy testing of some chemical disinfectants, but in 1982 this was stopped, reportedly for budgetary reasons. Thus, manufacturers presently do not need to have microbiologic activity claims verified by the EPA or an independent testing laboratory when registering a disinfectant or chemical sterilant (700). This occurred at a time when the frequency of contaminated germicides and infections secondary to their use had increased (378). Investigations that demonstrated that interlaboratory reproducibility of test results was poor and manufacturers' label claims were not verifiable (387, 637) and symposia sponsored by the American Society for Microbiology (696) heightened awareness of these problems and reconfirmed the need to improve the AOAC methods and reinstate a microbiologic activity verification program. A General Accounting Office report, “Disinfectants: EPA Lacks Assurance They Work” (701), seemed to provide the necessary impetus for EPA to initiate some corrective measures, which include cooperative agreements to improve the AOAC methods and independent verification testing for all products labeled as sporicidal and disinfectants labeled as tuberculocidal. These measures will eventually improve the aforementioned problems if interest and funds are sustained. A list of products registered with the EPA and labeled for use as sterilants, tuberculocides, or against HIV and/or HBV is available through the EPA's Web site: http://www.epa/oppad001/chemregindex.htm. Organizations (e.g., Organization for Economic Cooperation and Development) are working to achieve harmonization of germicide testing and registration requirements. One of the difficulties associated with the evaluation of the bactericidal activity of disinfectants is preventing bacteriostasis due to disinfectant residues that are carried over into the subculture media. Likewise, small amounts of disinfectants on environmental surfaces may make it difficult to get an accurate bacterial count when performing microbiologic sampling of the healthcare environment as part of an epidemiologic or research investigation. One of the ways these problems may be overcome is by employing neutralizers that inactivate residual disinfectants (702, 703, 704). Two commonly used neutralizing media for chemical disinfectants are Letheen Media and D/E Neutralizing Media. The former contains lecithin to neutralize quaternaries P.1508 and polysorbate 80 (Tween 80) to neutralize phenolics, hexachlorophene, formalin, and, with lecithin, ethanol. The D/E Neutralizing media neutralize a broad spectrum of antiseptic and disinfectant chemicals, including quaternary ammonium compounds, phenols, iodine and chlorine compounds, mercurials, formaldehyde, and glutaraldehyde (705). A review of neutralizers used in germicide testing has been published (703). CONCLUSION When properly used, disinfectants can ensure the safe use of invasive and noninvasive medical devices. However, current disinfection guidelines must be strictly followed.
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Infectious diseases can be transmitted from one human to another by a number of different mechanisms. Some of these mechanisms such as aerosolized respiratory droplets pose a direct threat to persons nearby, whereas others involve direct contact or exposure to biologic specimens from infected patients. Healthcare workers, consequently, are known to be at risk for contracting an infection from patients or patient specimens (1, 2, 3, 4, 5, 6). Such risks for occupationally acquired infections in healthcare workers have long been appreciated, as is evident by the protective clothing once worn during the plague epidemic of the fourteenth century (Fig. 84.1). The evolving severe acute respiratory syndrome (SARS) epidemic (7), the threat of bioterrorism (8), and the ongoing acquired immunodeficiency syndrome (AIDS) epidemic (9) has focused considerable attention on occupationally acquired infections. Such attention has resulted in Centers for Disease Control and Prevention (CDC) infection control guidelines for SARS (10), Public Health Service (PHS) regulations for select agents and toxins (11), and Occupational Safety and Health Administration (OSHA) regulations for blood-borne pathogens (12). The reemergence of tuberculosis (13, 14) similarly has resulted in CDC guidelines (15) and federally mandated regulations (16). Figure 84.1. Protective garb worn by healthcare workers in the Middle Ages to protect themselves against plague. Several important references related to reducing the risk of occupationally acquired infections in healthcare workers are readily available. The National Committee for Clinical Laboratory Standards (NCCLS) offers Document M29-A2, “Protection of Laboratory Workers from Occupationally Acquired Infections” (17). The CDC also offers guidelines for infection control in hospital personnel (18). These guidelines include recommendations for nonpatient healthcare personnel, management of exposures, prevention of transmission of infections in microbiology and biomedical laboratories, and prevention of latex barrier hypersensitivity reactions. More persons in the United States today are employed in the healthcare sector than in any other industry (19). Historically, most of these workers have been employed in the hospital setting. Thus, occupationally acquired infections in healthcare workers have received the greatest attention for workers in the hospital setting. Hospitals have developed comprehensive infection control programs and occupational health services that address the prevention of occupationally acquired infections. However, as we enter the twenty-first century, the horizons of infection control are expanding (20) because of the recognition that the risk of infections transmitted from patients to healthcare workers is not limited to hospital workers but extends to out-of-hospital healthcare workers (21). Today, healthcare is delivered in outpatient, transitional care, long-term care, rehabilitative care, home care, and private office settings (22). The out-of-hospital setting is receiving increasing attention, and infection control requirements and activities have been established (23, 24). Chapter 83 covers the prehospital healthcare worker, whereas this chapter covers the prevention of occupationally acquired infections in posthospital healthcare workers. EXAMPLES OF POSTHOSPITAL HEALTHCARE WORKERS AND THEIR RISK FOR OCCUPATIONALLY ACQUIRED INFECTIONS The definition of posthospital healthcare workers continues to evolve (22). Outpatient healthcare workers and medical personnel at reference laboratories, for example, can be either prehospital or posthospital healthcare workers. Following are examples of common categories of posthospital healthcare workers and their risk for occupationally acquired infections. Pathologists and Medical Technologists Although pathologists and medical technologists generally work in the hospital setting, they may be involved in either hospital care or posthospital care. For example, pathologists and medical technologists who are involved in surgical pathology, cytology, and clinical laboratories are usually involved in hospital care, whereas pathologists and morgue personnel involved in autopsies could be considered posthospital healthcare workers. Moreover, some pathologists and medical technologists work in reference laboratories that are not associated with a hospital. As nonhospital-associated freestanding operations, these reference P.1450 laboratories most often do not have the assistance of hospital infection control professionals and, hence, may fall short in providing protective measures appropriate to the infectious risks. The use of such freestanding reference laboratories for testing of specimens from hospitalized patients and for testing of specimens from patients in the prehospital and posthospital setting is increasing. This, in turn, has resulted in potential infectious risks for personnel involved in the packaging, handling, and transport of medical specimens. Accordingly, the PHS and NCCLS have developed regulations and guidelines for proper procedures for the handling and transport of diagnostic specimens and etiologic agents (11, 25). Moreover, NCCLS, the CDC, and the National Institutes of Health (NIH) address biosafety issues in microbiology and biomedical laboratories (17, 26). All pathologists and medical technologists have unique risks for occupationally acquired infections because of contact with patient specimens. The risk for pathologists and medical technologists involved in clinical laboratories is covered in Chapter 82. The risks for pathologists who perform autopsies (17, 27) are addressed in this chapter. Biosafety considerations for autopsies are important topics that often are not addressed by hospital infection control committees. Home Healthcare Workers Cost containment has shifted a great deal of medical care from the hospital setting to the outpatient setting. Although the home setting is considered to have fewer infection risks, studies have not confirmed this (28). Clearly some patients receiving home healthcare have infections and, thus, pose a risk for home healthcare workers (29). These patients are often elderly and may have unrecognized tuberculosis (30). AIDS patients are another group of patients commonly cared for in a domiciliary setting (31). Such infection risks in the home healthcare setting are only beginning to be studied. Research is needed to delineate such risks and to identify ways to minimize or prevent these infections from being transmitted to home healthcare workers. This topic is discussed in Chapter 107. Residential Long-Term Healthcare Workers The number of persons entering assisted living facilities and nursing homes for residential long-term care is substantial and is increasing. Many of these nursing home, residential care, and assisted-living patients enter such facilities directly from the hospital. The need for residential long-term care facilities to provide comprehensive infection control programs is well recognized (32). A number of infectious diseases problems are common to long-term care facilities and often are unappreciated (33). Atypical presentation of infections is generally acknowledged and may lead to delays in diagnosis and treatment of infections such as tuberculosis. The physical plant of many long-term care facilities is often a factor; many residents live in confined settings with few private rooms, and rooms appropriate for isolation often are not available. Finally, many long-term care facilities experience rapid turnover of personnel, and residential long-term care workers frequently have less training than those in the hospital setting. Long-term care facilities need a well-developed infection control program that in part identifies and minimizes the risk of occupationally acquired infections. Such programs can be developed best with the assistance of the hospital-based infection control professional (34). (See Chapter 106.) Outpatient Healthcare Workers The delivery of healthcare continues to shift from the hospital setting to the outpatient setting (22). For example, an increasing number of surgical procedures are done on an outpatient basis, and postoperative complications are now seen by emergency departments (35). Thus, many outpatient healthcare workers can be considered posthospital workers and share the risks of posthospital healthcare workers. The Joint Commission on Accreditation of Healthcare Organizations (JCAHO) is actively reviewing infection control programs for outpatient services that are affiliated with hospitals. Rehabilitation Facility Workers Another shift in providing healthcare has been the establishment of rehabilitation facilities. Follow-up care of many illnesses is now carried out in these facilities, and nosocomial infections are common (36). Healthcare workers in these facilities have similar risks to hospital workers, yet these rehabilitation facilities may not be associated with a hospital and have access to infection P.1451 control professionals and policies. Surveillance and infection control measures, nonetheless, are needed. Dialysis Facility Workers Freestanding dialysis facilities have become very common. Clearly, the risk for many blood-borne pathogens in such facilities is high (37). These centers may not have access to infection control professionals and policies; however, surveillance and infection control measures clearly are needed. Healthcare Laundry Workers Freestanding healthcare laundries serving multiple hospitals have been established in many cities. The risk for these workers is high for certain infections, including blood-borne pathogens because of the presence of sharp objects such as needles (38). Workers in these laundries also are at risk for scabies. Laundries may not have access to infection control professionals and policies. Funeral Home Workers The risk for exposure to infectious agents during autopsies is becoming better known and has resulted in guidelines for performing autopsies to minimize this risk (17, 27, 39). In particular, guidelines designed to minimize the risk of human immunodeficiency virus (HIV) infection have been developed (40, 41). Funeral home workers can be considered posthospital healthcare workers and share some of the same risks as a pathologist performing an autopsy (42). A study of funeral practitioners has noted a low rate of occupational exposures and a high rate of hepatitis B vaccination in comparison with prior studies, which suggests both improved education for and compliance with the recommendations for preventing transmission of blood-borne pathogens in the workplace (43). Such efforts should be continued. Trash Haulers and Landfill Operators The potential for exposure to infectious diseases in trash haulers and landfill operators is a very important issue (44, 45). Although minimal (46, 47), the risk is real and should be controlled. The proper disposal of medical waste is a key factor in controlling this risk; NCCLS Document GP5-A “Clinical Laboratory Waste Management: Approved Guideline” addresses this topic (48), and federal law now requires compliance (49). (See Chapter 100.) EPIDEMIOLOGY OF OCCUPATIONALLY ACQUIRED INFECTIONS Although quite a few pathogens can be transmitted to a worker in the healthcare setting, there are relatively few mechanisms by which such transmission can occur. The most common and important mechanisms of transmission are exposure to aerosols, exposure to blood or body fluids via direct contact or inoculation, and hand-to-mouth transmission. These are reviewed in some detail. Exposure to Aerosols The transmission of Mycobacterium tuberculosis occurs mainly by inhalation of droplet nuclei (50). There is also evidence that in some cases the coronavirus responsible for SARS has been spread by droplet nuclei (7). These droplets are airborne particles and must be less than 5 Вm in size to reach the alveolar spaces. Droplet nuclei can be produced when persons with pulmonary or laryngeal infections speak, sneeze, cough, or sing. If these persons are in a healthcare setting such as a nursing home, and the diagnosis of tuberculosis or SARS is unknown, they become a risk to healthcare workers. Healthcare workers in laboratories are also at risk for airborne pathogens, because there are certain manipulations with patient samples that may produce an aerosol. An important example of such a manipulation is dropping of fluids containing microbial suspensions (e.g., urine containing M. tuberculosis microorganisms because of renal tuberculosis) onto a hard surface, producing an aerosol. Working with Neiserria meningitidis cultures are also considered a risk, and microbiology technologists should be immunized against this pathogen. The risk of aerosolized M. tuberculosis from patients with unsuspected tuberculosis to posthospital healthcare workers such as home healthcare, nursing home, and clinic healthcare workers has become quite clear with the resurgence of tuberculosis in the United States. This risk increases in settings such as outpatient clinics where many sick people congregate in waiting and treatment rooms or halls and is also increased in communities where the incidence of HIV and/or tuberculosis is high. Outbreaks of tuberculosis among healthcare workers have occurred (51, 52, 53); some have involved multidrug-resistant M. tuberculosis (52, 53). This risk can best be appreciated by considering the tuberculosis skin test conversion rates among healthcare workers that have ranged from 0.11% to 10% (54, 55). This risk increases considerably in healthcare workers who are exposed to persons from countries where tuberculosis is endemic, to HIV patients, and to patients known to have tuberculosis; the skin test conversion rates in such settings have ranged from 18% to 55% (56, 57). Transmission of tuberculosis to healthcare workers can be a major problem requiring prevention and control (57). This problem is covered in great detail in Chapter 37. A less well-appreciated, but equally important, risk for posthospital healthcare workers such as pathologists and funeral home workers is the risk for aerosolized transmission of infectious agents when working with deceased patients (58). In addition to the risk of dropping body fluids containing microbial suspensions, a number of other procedures associated with autopsies produce an aerosol. For example, the Rokitansky method, in which the abdominal and thoracic organs are eviscerated as a unit, continues to be commonly used at autopsy. However, this method involves blunt blind dissection in both cavities, which is cumbersome and creates unnecessary aerosols. The NCCLS now recommends removing organs singly (the Virchow technique) to avoid the more hazardous aerosolization risk associated with complete evisceration by the Rokitansky method (17). P.1452 The NCCLS also recommends that organs not be photographed until they have been fixed in formalin to decrease the risk of aerosolized microorganisms. Unfortunately, this does not provide complete protection against aerosolized M. tuberculosis because this pathogen survives fixation in formalin, although the fixation does decrease the number of mycobacteria and thus lessens the degree of infectivity (59). The need to saw the calvarium is perhaps the most problematic autopsy procedure, because it unavoidably creates an aerosol. Aerosolization can be minimized by doing this procedure inside a plastic bag or plastic head frame, using a hand saw (difficult to do), or having a vacuum attached to the oscillating saw. Another important risk factor for aerosolization during an autopsy is the use of side-arm faucet water aspirators to remove pleural or peritoneal fluids from these body cavities, because these aspirating devices produce an infectious aerosol. Side-arm faucet water suction devices should not be used in autopsy suites or in funeral homes. Instead, they should be replaced by surgical-type vacuum reservoirs that are attached to the hospital vacuum lines that have appropriate traps, filters, and regulators (60). Air flow in the autopsy suites (but not funeral homes) has been addressed by the American Society of Heating, Refrigerating, and Air Conditioning Engineers and by the CDC (15). Adequate air flow is an important means of minimizing the risk of aerosolized pathogens. Both groups recommend that autopsy suites have at least 12 total air exchanges per hour and that autopsy room air be exhausted directly to the outside. In addition, the College of American Pathologists recommends that autopsies on high-risk patients be done only in rooms with good ventilation (60, 61). It is important to have a clear understanding of what constitutes good ventilation. There are three important engineering factors that allow good ventilation/control of air within a room. First, negative pressure in the room should be maintained with respect to surrounding areas. This means that air should move from an area of low infectivity (i.e., outside the room) to an area of higher infectivity (i.e., inside the room). Second, the number of air changes in the room should be increased, which can substantially decrease the risk of the transmission of aerosolized pathogens by dilution and removal of these pathogens. Good ventilation also dictates that within-room mixing of air (i.e., ventilation efficiency) is adequate. This is usually accomplished by placing air supply outlets in the ceiling and exhaust inlets near the floor. This provides a downward movement of clean air, which travels through the breathing zone to the floor area for exhaust. Third, there should be adequate exhaust to the outside. Because the air in a high-risk room such as the autopsy suite is likely to be contaminated with infectious droplet nuclei, it should not be recirculated within the room or within the building. Instead, this potentially contaminated air should be exhausted to the outside, away from intake vents, people, and animals. An episode in a medical examiner's office in Syracuse, New York, (53) illustrates this point. Two workers in the Onondaga County medical examiner's office