F
Respiratory Protection and Control of Tuberculosis in Health Care and Other Facilities

Philip Harber, Scott Barnhart, Douglas Hornick, and Robert Spear*

In 1994 guidelines, the Centers for Disease Control and Prevention (CDC) recommended a hierarchy of infection control measures for tuberculosis (CDC, 1994). The hierarchy consists of administrative controls, followed by engineering controls and then personal respiratory protection. This paper examines the last step in the hierarchy: the use of personal respiratory protection devices to shield health care workers when they enter areas (e.g., a tuberculosis isolation room) where the air may contain Mycobacterium tuberculosis aerosol.

The respiratory protection provisions of the 1997 proposed rule from the Occupational Safety and Health Administration (OSHA) (62 FR 201 [October 17, 1997]) are generally similar to the CDC guidelines. One exception—and the major area of controversy—involves the requirement for annual fit testing of individuals who use or may use personal respirators.

The next sections of this paper describe the basic components of a respiratory protection program, the types of respiratory protection devices used to prevent transmission of tuberculosis; and methods for fit testing the devices. The remainder of the paper then considers evidence about the effectiveness of respiratory protections in reducing the occupational risk of tuberculosis.

*  

Philip Harber is Professor at the Department of Family Medicine, University of California Los Angeles. Scott Barnhart is Medical Director, Harborview Medical Center, Seattle Washington. Douglas Hornick is Associate Professor at the Division of Pulmonary Diseases and Critical Care Medicine, University of Iowa, Iowa City. Robert Spear is Professor of Environmental Health Sciences at the University of California at Berkeley.



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Tuberculosis in the Workplace F Respiratory Protection and Control of Tuberculosis in Health Care and Other Facilities Philip Harber, Scott Barnhart, Douglas Hornick, and Robert Spear* In 1994 guidelines, the Centers for Disease Control and Prevention (CDC) recommended a hierarchy of infection control measures for tuberculosis (CDC, 1994). The hierarchy consists of administrative controls, followed by engineering controls and then personal respiratory protection. This paper examines the last step in the hierarchy: the use of personal respiratory protection devices to shield health care workers when they enter areas (e.g., a tuberculosis isolation room) where the air may contain Mycobacterium tuberculosis aerosol. The respiratory protection provisions of the 1997 proposed rule from the Occupational Safety and Health Administration (OSHA) (62 FR 201 [October 17, 1997]) are generally similar to the CDC guidelines. One exception—and the major area of controversy—involves the requirement for annual fit testing of individuals who use or may use personal respirators. The next sections of this paper describe the basic components of a respiratory protection program, the types of respiratory protection devices used to prevent transmission of tuberculosis; and methods for fit testing the devices. The remainder of the paper then considers evidence about the effectiveness of respiratory protections in reducing the occupational risk of tuberculosis. *   Philip Harber is Professor at the Department of Family Medicine, University of California Los Angeles. Scott Barnhart is Medical Director, Harborview Medical Center, Seattle Washington. Douglas Hornick is Associate Professor at the Division of Pulmonary Diseases and Critical Care Medicine, University of Iowa, Iowa City. Robert Spear is Professor of Environmental Health Sciences at the University of California at Berkeley.

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Tuberculosis in the Workplace COMPONENTS OF A RESPIRATORY PROTECTION PROGRAM A respiratory protection program has several components, of which the respirator (mask) device is only one (Vesley, 1995; Schaefer, 1997). Other elements include Assessment of individual worker’s exposure to a hazard Selection of appropriate respirator for that exposure Proper maintenance and storage of reusable respirators Employee education and training Medical certification of worker’s ability to wear respirator safely Periodic audit of the respirator program Designation of individual responsible for program In addition to explaining the rationale for respirator use and the proper way to use a respirator, the education and medical evaluation components of a respirator program should explain potential adverse effects of respirator use, such as interference with voice, breathing discomfort, and stress. A respiratory protection program involves several steps in a sequential process (Harber et al., 1999). These steps, designed for other industries but generally applicable to tuberculosis control programs, include the following: Identifying work sites with potential for significant exposure to an airborne hazard Identifying specific workers at risk and any characteristics that might make them especially at risk from the hazardous agent Determining the magnitude of the risk by work site and worker tasks Identifying a respirator that will prevent inhalation of the hazardous agent in the airstream Assessing adequacy of respirator fit (i.e., proportion of airflow actually going through the filter medium rather than between the respirator seal and the wearer’s face) Ensuring that exposed workers actually use the respirator and use it correctly The last element is crucial. A perfect respirator is of little value unless the proper worker uses it at the proper time. While this is intuitively obvious, not all analyses have considered this broad perspective. A quantitative analysis showed that there is an asymptotic effect of noncompliance with program elements (Harber et al., 1999). That is, a high protection factor of the device itself cannot compensate for programmatic failure or individual worker behavior deficits.

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Tuberculosis in the Workplace TYPES OF RESPIRATORY PROTECTION DEVICES Respirators (respiratory personal protective devices) are widely used for protection against inhaled toxins. The two major categories of respirators are air-purifying devices and atmosphere-supplying devices. Air-purifying respirators function by partially “cleaning” the inhaled the air (filtering out hazardous agents), whereas atmosphere-supplying respirators provide an independent source of air. The 1994 CDC guidelines established performance criteria for respirators employed to prevent transmission of M. tuberculosis. Currently, the National Institute for Occupational Safety and Health (NIOSH) lists four types of personal respirators for use as protection against tuberculosis. The devices are listed below in appropriate order of common use, convenience, and cost. N95 and other disposable particulate respirators: These respirators are relatively simple, disposable devices and are now widely used for protection against occupational tuberculosis. Although they look like surgical masks, these devices are fundamentally different in construction and function. Powered air-purifying respirators (PAPR): The powered air-purifying respirator provides a greater degree of protection than the N95 respirator. It consists of a tight-fitting face mask or a loose-fitting hood or helmet that is attached by a hose to a battery-operated fan that blows filtered air into the mask. Replaceable particulate filter respirators: External air-filtering cartridges are attached externally to the mask device itself. These devices are widely used in chemical industry and other settings and come with either half-masks or full facepiece masks. Postive-pressure supplied-air respirators: These respirators use compressed air delivered to a half or full facepiece mask through a hose from a fixed source. Other types of devices have been used in the past. Dust-mist (DM) and dust-mist-fume (DMF) respirators have been widely used in industry and were used for tuberculosis protection during hospital outbreaks in the late 1980s and early 1990s. High-efficiency particulate air respirators (HEPA) are effective at removing smaller particles than the DM and DMF devices and began to supplant the DM and DMF respirators for tuberculosis protection before being largely replaced by N95 devices and, infrequently, PAPRs. The mask type for a respirator is constructed to meet the specific application needs. For tuberculosis control and a number of other uses, the mask itself generally contains the filtration medium. This contrasts with devices commonly used for many chemical exposures, in which the

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Tuberculosis in the Workplace mask is responsible for directing airflow, but the adsorbent or filter medium is in a cartridge or canister attached to the mask. N95 and particulate filter respirators require that the individual generate (by breathing) the negative pressure necessary to force air in through the filtration medium. PAPRs use a pump to push ambient air through the filtration medium and supply it to the mask. In addition to obviating the need for the user to perform the ventilatory effort to overcome the resistance of the filtration medium, the PAPR supplies air within the mask at positive pressure relative to the ambient atmosphere. Thus, if the facial seal is not perfect, air will tend to flow from within the mask to the outside because of the pressure gradient. In contrast, most negative-pressure respirators require inhalation effort by users to create negative pressure within the mask. For these devices, if a leak exists at the facial sealing surface, the mask will draw in ambient untreated air. Hence, PAPRs typically provide a higher degree of protection than the typical negative-pressure masks. The former are, however, cumbersome, costly to maintain, and somewhat difficult to use. Some respirators are intended as single-use devices, designed to be discarded after one use. Others may be considered reusable, meaning that they may be employed more than once, but are not meant to be permanent and durable devices. Many of the respirators marketed for tuberculosis control fall in this category. Finally, respirators may be designed as long-lasting, multiuser pieces of equipment. Respirators also differ in the degree to which they resemble the typical surgical mask, which is more familiar to patients and possibly less anxiety inducing than some other types of devices. Some respirators are designed so that the user exhales through the filtering medium, whereas others have special exhalation valves. Such valves may make exhalation more comfortable, but they allow patients to be exposed to unfiltered air from the wearer, so such devices are not to be used during surgery. Masks may be constructed of a soft, flexible material or of a more rigid elastomeric material. More rigid materials generally provide a better (i.e., tighter) fit but may be more uncomfortable. Different masks cover different amounts of the face. A quarter mask covers the mouth and nose and seals between the lower lip and the chin, whereas a half mask seals underneath the chin. A full-face mask extends from below the chin to above the forehead. In general, larger masks seal more effectively than the smaller types, but they are more expensive and cumbersome. In the United States, respirator designs must be certified by NIOSH. The certification process includes examination of the design, laboratory testing of devices supplied by the manufacturer, audit of the production process, and occasional testing of off-the-shelf devices (Hodous and Coffey, 1994). In the early 1990s, during the resurgence of tuberculosis in United States, NIOSH classified air-purifying respirators for removing particles

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Tuberculosis in the Workplace (appropriate for tuberculosis protection) as dust-mist, dust-mist-fume, or HEPA (high-efficiency particulate air). A large gap in the efficiency of the particulate filtration process differentiated the first two types of devices and the HEPA type. Only the HEPA type, which was much more expensive, met the performance criteria for tuberculosis protection described by CDC in the 1993 draft and 1994 final guidelines. In 1995, NIOSH certified a new class of devices known as the N95 type. This relatively inexpensive type of respirator is designed to be at least 95 percent efficient at removing particulates, which meets the CDC performance criteria. METHODS FOR FIT TESTING OF RESPIRATORY PROTECTION DEVICES Fit testing is the process of determining the extent to which the facial seal of the respirator prevents inward leakage of unfiltered air. It may be applied at several different points: To test the newly designed respirator To evaluate an individual worker prior to placement in a job with potential mycobacterial exposure To evaluate an employee whenever a new respirator type is provided To evaluate fit on a regularly scheduled basis (e.g., annually) Respiratory protection programs for tuberculosis are currently exempt from the 1998 OSHA respiratory protection standard, which requires annual fit testing. Pending publication of the occupational tuberculosis standard, they are subject, instead, to special regulations that do not mandate annual testing. The 1997 proposed OSHA rule on tuberculosis would require annual fit testing. Methods of Determining Adequacy of Fit Respirator fit describes the degree to which the device effectively limits the air leakage around the filtration media or, in some cases, between the user’s face and the sealing surface of the respirator. Traditionally, protection is described in terms of the Protection Factor (PF). This is the ratio of the material outside the mask to its concentration inside the mask. It is affected by two factors: first, the degree to which the medium cleanses air moving through it, and second, the degree of leakage at the facial sealing surface of the user. Protection factor is typically measured using a marker chemical agent. Determination of the Protection Factor is based upon measurements using surrogate marker materials. For example, sodium chloride aerosol is commonly employed for certification of respirator design types. In in-

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Tuberculosis in the Workplace dustrial settings where a specific chemical agent is employed, one may measure its concentration inside and outside of the mask to develop a meaningful protection factor measurement. Or, if the agent is particularly dangerous, a marker material with similar characteristics may be employed. For tuberculosis, however, this is infeasible since measurement of tuberculosis agents in air is difficult. Therefore, protective efficacy is generally estimated based upon the respirator characteristics for chemical, rather than biologic, agents.1 Categories of Fit Test There are two types of fit tests—quantitative and qualitative. In addition, workers should be trained to check the seal on their respirator at each use. The cost and applicability of these differ significantly. In a quantitative fit test, the concentration of a marker material inside and outside the mask is determined empirically. Quantitative fit testing is more accurate but requires trained personnel and relatively complex equipment. In a qualitative fit test, a pass/fail approach is used. An individual dons the mask, and a test material is placed in the surrounding ambient air; then, the user reports whether it passes through the respirator. For example, saccharin aerosols are detectable by their sweet taste if the respirator does not effectively remove them (e.g., because of leakage at the face seal surface). Although NIOSH recommends against it, irritant smoke is also occasionally used in a qualitative fit testing procedure. In a user seal check (commonly called a fit check) procedure, the user performs a simple maneuver to determine if the seal is adequate in an approximate, qualitative fashion. For example, the user may obstruct the inlet ports and attempt to inhale; passage of air implies that there is significant leakage at the facial sealing surface. This type of assessment is performed by the individual each time he or she dons a mask. During quantitative or qualitative fit tests, testers also evaluate potential physical characteristics or changes such as weight gain or loss that might affect respirator fit. Quantitative testing is difficult for certain mask 1   There are several formats for expressing Protection Factor. The Assigned Protection Factor is assigned based upon the mask type design. Although it may have been based upon empiric data, it is not measured specifically for the individual user. Conversely, the Protection Factor for a particular respirator and user may be determined under laboratory testing circumstances. However, efficacy of protection (PFs) under ideal laboratory circumstances does not represent “real-life” utilization. Therefore, the Workplace Protection Factor (WPF) describes the actual Protection Factor under field-use conditions. As might be expected, there are significant disparities between the Assigned Protection Factor, the laboratory-measured Protection Factor, and the actual Workplace Protection Factor.

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Tuberculosis in the Workplace types. It requires a probe inside the mask to measure the concentration of the marker material. This is generally not feasible with single-use/disposable respirators. Fennelly (1997) noted that there have been very few actual quantitative fit tests with the disposable types of respirators now in common use. Until recently, probe devices were not available to perform quantitative assessment of the actual filtration efficiency of these masks when used by humans. (See Coffey et al., 1999.) Quantitative fit testing requires technical prowess, which ideally would be supplied by a trained industrial hygienist. Although there are 7000 hospitals, there are only 5,000 industrial hygienists in United States. Therefore, if widespread use of quantitative fit testing were required for hospitals and other facilities, other alternatives might be needed. Qualitative fit testing, which relies upon subjective responses of the user to substances such as saccharin, is less expensive and less technically demanding. It is therefore attractive to employers. Qualitative fit tests have limitations. Saccharin is avoided in many settings because of its reputation as a carcinogen, and some hospitals have stopped using irritant smoke because this may provoke asthma (Fennelly, 1997). Bitrex, an extremely bitter compound sometimes used to deter children from eating poisonous household products, may offer a good alternative. Except during nonhuman laboratory testing in research settings, fit testing cannot be performed with the actual exposure agent of concern (mycobacteria). Nevertheless, laboratory studies have demonstrated that surrogate agents are adequate (Qian et al., 1998). Issues in Fit Testing The discussion above has mentioned several concerns about the role and burden of fit testing in the context of programs to prevent tranmission of M. tuberculosis in health care and other settings. These include the effectiveness and feasibility of quantitative versus qualitative fit testing, the selection of particular agents for use in qualitative testing, and the trade-offs between protection and worker comfort and willingness to use the masks consistently and correctly. Traditional occupational medicine/industrial hygiene practices require that the fit testing be repeated whenever a new respirator type is chosen. This presupposes that differences among masks are so great that successful fit with one does not predict adequacy of another of the same class. Implementation of this requirement may create unique problems for tuberculosis prevention in hospitals. Workers may be employed in several different settings, and purchasing agents often change availability of particular brands based upon availability/cost. Because the at-risk population is amorphous, such a fit testing requirement might be particularly difficult to implement and enforce reliably.

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Tuberculosis in the Workplace EVIDENCE OF EFFECTIVENESS OF RESPIRATORY PROTECTION: FACILITY STUDIES AND SURVEYS Unfortunately, no research has tested individually the effects of respiratory protection on health care workers’ risk of acquiring tuberculosis infection or disease. Some studies do, however, include relevant findings about the mix of measures implemented following hospital outbreaks of tuberculosis in the late 1980s and early 1990s. Three reports describe hospital responses to well-recognized outbreaks of tuberculosis (two of which involved multidrug-resistant disease) (Wenger et al., 1995; Maloney et al., 1995; Blumberg et al., 1995). In each of the hospitals, the outbreak was ended effectively using variable levels of the tuberculosis control hierarchy. Most important, nosocomial tuberculosis transmission from patient to health care worker was interrupted. Although the hospitals continued to care for substantial numbers of patients with tuberculosis, health care worker exposure incidents and tuberculosis skin test conversions dropped substantially. Table F-1 summarizes the control measures implemented. Each institution implemented extensive administrative controls, in particular, protocols to promptly identify, isolate, evaluate, and, as appropriate, treat people with signs and symptoms of tuberculosis. Each institution also implemented variable engineering controls, usually some kind of negative-pressure isolation room. Each institution supplied workers with some kind of respiratory protection device. It is important to note that hospital responses—including the provision of respirators to workers—predated the 1994 CDC guidelines, which specified performance criteria for respiratory protection devices. They also predated NIOSH’s 1995 certification of the N95 respirator, which met the new CDC criteria but was less expensive than previously certified devices. In any case, the respiratory protection measures implemented in these institutions were less stringent than those set forth in the 1994 CDC guidelines, the 1997 proposed OSHA rule on occupational tuberculosis, or the 1998 OSHA TABLE F-1. Measures Used to Control Outbreaks of Nosocomial Tuberculosis Transmission in Three Hospitals   Control Measure(s) Used Hospital Administrative Measures Engineering Measures Respiratory Protection Device Jackson Memorial, Miami Extensive Extensive Submicron Cabrini, New York Extensive Exhaust fansa Molded surgical Grady Memorial, Atlanta Extensive Exhaust fansa Submicron aExhaust fans were placed in windows to produce negative pressure in isolation rooms.   SOURCE: Adapted from McGowan (1995).

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Tuberculosis in the Workplace respiratory protection standard for other hazards. Again, the outbreak studies suggest that the administrative controls adopted by hospitals played the major role in ending the outbreaks and that the kinds of respiratory protections they implemented added little. It is also illustrative to examine two reports from nonoutbreak hospitals that had relatively high admission rates for patients with active tuberculosis and had adopted tuberculosis control measures to reduce their potential for outbreaks. As summarized below, these reports also suggest a limited role for respiratory protections. Again, all control measures were adopted prior to the 1994 CDC guidelines and the NIOSH certification of N95 respirators. In May 1992 Columbia-Presbyterian Hospital in New York City revised its infection control program to be consistent with the 1990 CDC guidelines (Bangsberg et al., 1997). The facility had not experienced an outbreak of tuberculosis, but administrators were concerned about the potential for an outbreak based on reports from other city institutions. Columbia first (May 1992) instituted extensive administrative controls that emphasized stricter respiratory isolation policies; shortly thereafter (July 1992), it installed two tuberculosis isolation rooms in the emergency department. In July 1993, the hospital began to require that medical house staff don a 3M disposable respirator to enter respiratory isolation rooms; they provided surgical masks prior to that. House staff were fit tested and instructed in the use of the new devices. The tuberculin skin test conversions among house staff dropped from 10 percent preimplementation to 0 percent to 2 percent for time intervals after implementation of the administrative controls and engineering controls but before the provision of new respirators. The authors felt that administrative controls were the main reason for the improvements observed. St. Clare’s Hospital in New York City implemented the 1990 CDC guidelines in 1991 (Fella et al., 1995). This hospital focused first on administrative controls (especially, early recognition and isolation of patients with active tuberculosis) and then on engineering controls (including installation of 44 negative-pressure isolation rooms in a 2-year period and installation of ultraviolet [UV] germicidal irradiation lights in patient rooms and general use-areas). The institutions made a series of changes in the respiratory protection devices provided employees (switching in January 1992 from the Technol shield to a particulate respirator, then in January 1993 to a dust-mist-fume respirator with fit testing beginning in June 1993, and, finally to HEPA respirators in 1994 after the study period ended). From 1991 to 1993, the tuberculin skin test conversion rate among health care staff fell from 20.7 percent in the first 6-month testing interval to a range of 3.2 to 6.2 percent over subsequent 6-month intervals. Changes in conversion rates were not associated with changes in personal respiratory protection.

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Tuberculosis in the Workplace Another report on the experience of a Chicago hospital suggests that personal respirators do not compensate for inadequate engineering controls. Kenyon and colleagues (1997) reported an outbreak of multidrug-resistant tuberculosis in a facility that had provided and fit-tested workers with high-efficiency particulate respirators but that had no isolation rooms that met CDC criteria. Delays in recognizing and treating infectious patients also contributed to the outbreak. Three of the 11 previously skin test negative workers who converted their tuberculin skin test (including one ward secretary with no patient care responsibilities) had no contact with the source case patients. The authors conclude that a respiratory protection program alone cannot protect all workers. In the absence of appropriate isolation rooms, air that escapes from rooms housing infectious patients can infect those outside the room. Also pertinent is a survey of 52 former house staff who served in the tuberculosis facility associated with the University of Virginia between 1979 and 1987 (Jernigan et al., 1994). The 52 individuals had experienced a total of 70 6-week rotations in the facility, which had negative-pressure isolation rooms and ultraviolet germicidal radiation. A simple surgical mask (no fit-testing program) was the only form of respiratory protection used. Those surveyed reported no skin test conversions associated with the rotation. In another survey, the Society for Healthcare Epidemiology (SHEA) surveyed member hospitals for tuberculosis control practices from 1989 to 1992 and evaluated responses from 210 hospitals (Fridkin et al., 1995a,b). Four control practices described in the 1990 CDC guidelines were evaluated: (1) placing known or suspected tuberculosis patients into a single room (or a room shared by two such patients); (2) negative-pressure ventilation of the isolation room, (3) at least 6 or greater air changes per hour in isolation rooms; and (4) air exhaust directly to the outside. For the sub-group of hospitals that admitted at least six or more tuberculosis patients per year and met all four criteria, the tuberculin skin test conversion rate among health care workers was significantly less for those hospitals compared to those for others (0.6 versus 1.89 percent; p = 0.02). Conversion rates were not associated with type of respiratory protection. The survey did not cover fit testing. In all of the reports cited above, the implementation of tuberculosis control measures was associated with low levels of tuberculosis transmission among health care workers in hospitals where tuberculosis was prevalent. These data, although imperfect and limited, support CDC’s emphasis on administrative controls and suggest the lesser contribution of a respiratory protection program in the hierarchy of tuberculosis infection control. Admittedly, the data lack sufficient power to support firm conclusions. Such conclusions would require well designed, prospective controlled studies to investigate specifically the independent contribution

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Tuberculosis in the Workplace of a respiratory protection intervention. Until such data are available (and it is far from clear that the necessary studies will be undertaken), the appropriate level of respiratory protection will likely continue to be an area of debate. MODELING STUDIES PROJECTING EFFECTS OF RESPIRATORY PROTECTIONS It is not a surprise to find that observational studies of the effects of implementing tuberculosis controls in health care setting have not clearly demonstrated the independent effect of the respiratory protection components of these programs. In large part, this is due to the simultaneous implementation of several control improvements with the consequent inability to contrast outcomes where individual elements of the control program are present versus when they are absent. In addition, the studies typically involve relatively small numbers of workers who convert their tuberculin skin tests following periodic (usually yearly) testing. If respirators have a small but positive effect, such studies (and epidemiologic studies generally) will lack the statistical power to detect the effects. Much of the literature on respirator efficacy is based on theoretical and empirical data which demonstrates that respirators can reduce the exposure to airborne contaminants by factors ranging from 2.4 to greater than 200 (Barnhart et al., 1997). Two papers have modeled the potential for respirators to reduce risk for tuberculin skin test conversion based on data from a series of elegant experiments by Riley and colleagues (Riley et al., 1959, 1962). First, Riley and colleagues noted the rate at which nurses converted their skin tests in tuberculosis wards and calculated on the basis of their expected minute ventilation the estimated concentration of infectious particles in the air of these wards. Then based on these estimates they performed an experiment using guinea pigs as a bioassay and calculated the average airborne production of infectious particles generated by patients with infectious tuberculosis. These data based on direct monitoring of tuberculosis infection from airborne droplet nuclei provide, perhaps, the strongest data on risks to workers exposed to patients with infectious tuberculosis. In two complementary papers Barnhart and colleagues (1997) and Fennelly and Nardell (1998) model the potential benefits of respiratory protection. Both papers rely on published estimates of the ability of respirators to reduce exposure to airborne particles. Inherent in this reliance is an assumption that tuberculosis particles or droplet nuclei will be filtered out by the medium just as other hazardous particles such as silica, asbestos, or plutonium are. While it is well recognized that fit factors under static conditions vary considerably from those under work conditions,

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Tuberculosis in the Workplace the general principle of respirators reducing exposure is well accepted (Houdous and Coffey, 1994). Barnhart and colleagues, using the data of Riley and colleagues (1959) on concentration of infectious particles, estimated that under average conditions of exposure it would take 2,650 person-hours to convert a tuberculin skin test in an unprotected worker. Risk of tuberculin skin test conversion was estimated to be reduced by the following proportions by using a respirator: surgical mask, 2.4-fold; disposable dust, fume, mist (analogous to N95), 17.5-fold; elastomeric HEPA cartridge respirator, 45-fold; and PAPR, 238-fold. Use of a dust-fume-mist respirator is estimated to increase the time to tuberculin skin test conversion from 2,650 to greater than 44,000 hours. Similar benefits were seen for increasing ventilation and use of ultraviolet germicidal irradiation. Using the data of Riley and colleagues, for a lifetime exposure to infectious patients of 250 hours, the risk of a tuberculin skin test conversion for an unprotected worker was estimated to be 9 percent. For these reasons, use of a respirator under conditions of exposure or risk was felt to be prudent. In this paper, benefit and risk are closely linked. In the absence of risk, of course, no benefit can be expected. Fennelly and Nardell (1998) also used the data of Riley and colleagues and very similar protection factors for respirators. They tested the hypothesis “that personal respiratory protection is relatively more efficacious in decreasing the risk of infection with Mycobacterium tuberculosis for exposures more highly concentrated aerosols or at low room ventilation rates, and conversely that respirators are relatively less efficacious as the concentration of the infectious aerosol decreases or as room rates increase. (Fennelly and Nardell, 1998, p. 754) Their estimates showed the risk of infection decreasing exponentially with increasing room ventilation or increasing personal respiratory protection. As concentrations of the infectious particles decrease, the relative efficacy of respirators decreases. They conclude that the risk of occupational tuberculosis probably can be lowered considerably by using relatively simple respirators, but in settings of higher risk (e.g., cough-inducing procedures) more sophisticated respirators may be needed. EVIDENCE OF EFFECTS OF WORKER TRAINING AND FIT TESTING Among health care infection control experts, the effectiveness of respirators is less controversial than the well-established view in the occupational health world that real-world effectiveness requires that respirator use be part of a broader respiratory protection program with quite specific elements. The OSHA 1998 respiratory protection standard (29 CFR 1910.134) makes these elements explicit. They include medical evaluation

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Tuberculosis in the Workplace of employees required to use respirators (which may be limited to a brief questionnaire), both initial and annual fit testing; employee training regarding the respiratory hazards that they face, and training in the proper use of the respirators themselves. While respirators that fit (i.e., have an acceptably low rate of leakage around the face seal) provide greater protection than those that do not, methods to ensure good fit are imperfect and still evolving, particularly for the N95 respirators. Laboratory studies by Coffey and colleagues (1999) showed that using N95 respirators reduced exposure to aerosolized particulates and that fit testing the respirators produced substantial reductions in exposure. However, when the most rigorous criterion for fit testing was used (the 1 percent pass/fail criterion recommended by American National Standards Institute and required by OSHA), a substantial majority of tested individuals failed the fit test for 17 of the 21 devices tested, that is, most people could not be successfully fitted. The required 1 percent pass/fail criterion is thought to be needed to achieve no more than 10 percent respirator face-seal leakage during normal use in the workplace. Currently, the main certified alternative to the N95 respirator would be the PAPR, which is much more cumbersome and expensive to buy and maintain. It also can interfere with communication and cannot be used when a sterile field is needed as in surgery. Coffey and colleagues suggested that the major source of variability is the N95 respirator design itself rather than the user-respirator interface. Several of the most inadequate devices accounted for most of the variability among test results. Interpersonal variability was lower if one excluded the worst device. The study of Chen et al. (1994) found analogous results. They demonstrated that there was considerable variability, but a single mask accounted for much of this. Excluding this one, the residual variability in leakage among the others was relatively low.2 At least one less extensive study has suggested that education may be as effective as fit testing in improving workers performance in adjusting their respirators correctly (Hannum et al., 1996). In that study, a hospital recruited workers to participate in one of three respirator training programs and to be tested afterward on their ability to correctly adjust the respirator’s fit and seal. They concluded that training was important but that it did not matter much whether the training included direct fit testing or a classroom demonstration of proper fit checking prior to each use of a respirator. (The devices in use were HEPA respirators rather than the N95 respirators now commonly used.) 2   Rather than emphasizing individual fit testing, fit testing at the premarketing stage to eliminate poor design might be more cost effective. The governmental design-certifying agency (NIOSH) could shift to manufacturers much of the burden of assuring that masks are designed to fit most users properly.

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Tuberculosis in the Workplace In a letter to the editor of the New England Journal of Medicine, Brown and colleagues (1994) discussed the value of fit testing for HEPA respirators. They report that 12 subjects passed an initial fit test but 4 of 12 failed when the test was repeated following actual use of their respirators. Deformation of the respirator was cited as the likely explanation. Thus, this short report suggests that passing a fit test may not assure adequate protection under actual use conditions. A reduction in protection may occur because of degradation of the mask, physical changes in the individual, or the need for reinforcement of proper technique. CONCLUSION Respiratory protection, particularly requirements for routine annual fit testing, is one of the most contentious elements of the 1997 proposed OSHA regulation on occupational tuberculosis. The challenge for policy makers is to craft reasonable, cost-effective policies in this area that (1) are based on the best available science (recognizing that much uncertainty still exists) and (2) match respiratory protection requirements to the degree of tuberculosis risk facing workers and institutions. Overall, the risk of occupational tuberculosis has been declining for health care, correctional, and other workers in recent years with adoption of community and workplace tuberculosis control measures. For example, since 1992, tuberculosis case rates have declined nationwide by 35 percent. In some cases, research and product development efforts may help policymakers devise feasible risk-sensitive policies. For example, CDC/ NIOSH has taken steps in this direction by testing and certifying N95 respirators, which are less costly than the HEPA respirators that they have largely replaced but still meet the criteria set forth by CDC in 1994. The agency has also tested different types of N95 respirators to identify deficient models, which may suggest the need for more attention to the manufacturing and premarketing stage (before a respirator reaches a user). Given that a major concern involves the burden of respiratory protection requirements for low-risk institutions and individuals, CDC/NIOSH should consider further research on (1) methods for risk categorization or stratification (based on probability of infection) of individuals and institutions caring for tuberculosis patients and (2) levels of respiratory protection that are appropriate (i.e., will reasonably reduce risk) for institutions or individuals with different levels of risk. Such research would provide policymakers and managers with better guidance on those situations that warrant minimal versus higher levels of respiratory protection.

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