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).
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.