Nettleman and colleagues [1] have provided an important contribution to the literature on the cost-effectiveness of respirators in preventing transmission of tuberculosis. We are concerned that they present a worst-case scenario and do not assess the use of respirators as part of a hierarchy of industrial hygiene interventions directed at risk reduction. This unfortunately limits the applicability of their results. For example, what if respirators were used for only some health care workers, visits to rooms were limited, reusable negative-pressure cartridge respirators were substituted (cost per use, $0.10 or less), patients were discharged in fewer than 14 days with directions on "source control" of coughing, changes in sputum collection procedures were implemented to allow for more rapid exclusion of uninfected patients from isolation, case identification were improved to limit unnecessary isolation, and purified protein derivative surveillance rates within the Veterans Affairs system were increased to ensure that estimates of employee risk could be adequately assessed? With these considerations in mind, we suspect that a national program to control tuberculosis transmission that places respirator use in the context of other administrative, source, and engineering controls may justify the costs associated with ensuring worker health. In addition, changes in criteria for respirators proposed by the National Institute for Occupational Safety and Health to meet the proposed standard may further decrease the economic burden.

We wish to offer a correction to the statement that "no evidence suggests that their use has ever prevented a single case of tuberculosis." Tuberculosis infection results from airborne spread of infectious particles. Respirators are designed to efficiently filter particles the size of droplet nuclei that contain Mycobacterium tuberculosis. Excellent data support the potential for well-fitted respirators to filter out droplet nuclei and to prevent infection. Finally, epidemiologic and experimental studies that document the efficacy of respirators do not exist. They are not likely to be done because of the ethical and logistic (sample size) constraints posed by such studies and because of the multiple reports of high incidence rates of tuberculosis among health care workers in some situations. Perhaps the more important questions to ask about respirator use are where, when, and in conjunction with which interventions should respirators be used to reduce workplace hazards?