We welcome the contribution of Maloney and colleagues [1] to the ongoing debate over appropriate respiratory protection of health care workers against tuberculosis. Jarvis and others at the Centers for Disease Control and Prevention (CDC) [2] also provided a comprehensive review of the difficulties that arise when well-intentioned initiatives by regulatory agencies are not supported by good science or are promulgated with insufficient data. Fortunately, additional data now support the efficacy of devices other than high-efficiency particulate air (HEPA) respirators for the protection of health care workers [3]. Moreover, the relative contribution of any particular type of respiratory protection toward minimizing nosocomial transmission of tuberculosis is probably minor compared with early patient identification, triage, and appropriate engineering controls. In both reported outbreak situations, molded surgical masks were useful as an adjunct to improvement in compliance with the CDC's 1990 tuberculosis guidelines on administrative and engineering controls.

Our concern, however, remains with a broader question: Can the approaches typically used by industrial hygienists and occupational health specialists to control and prevent occupational hazards be universally applied to all biological agents that a health care worker might encounter? Specifically, although we support discussion and scientific collaboration among the disciplines of occupational medicine, infection control, and applied epidemiology, premature implementation of broad mandates that are not supported by epidemiologic evidence appears problematic. For tuberculosis in particular, must we accept a previous investigation showing 1-to-2 CFU suspension of Mycobacterium tuberculosis causing infection in guinea pigs [4] as the sole basis for concluding that no permissible exposure level exists for this disease? Do we, in fact, need permissible exposure levels for tuberculosis? Epidemiologic studies in humans, not exclusively focused on unusual anecdotal instances of nosocomial transmission, should also be considered when guidelines or regulations are being developed [5]. We are concerned that some may view the success of these outbreak control measures only in this context and remain convinced that even a single aerosolized tubercle bacillus presents a risk to health care workers. We have observed that use of HEPA respirators at our institution has met considerable logistic obstacles (that is, concerns expressed by many affected health care workers that the respirators compromise their breathing and patient communication during prolonged use). We look forward to the final revised National Institute for Occupational Safety and Health certification process for respirators as a possible solution to the current HEPA conundrum.