Page:Niosh tb guidelines.pdf/22

Rh As a type of source control, it has been recommended that persons with infectious tuberculosis cover their noses or mouths when sneezing or coughing and wear surgical masks (15,52). As stated in 1990, both techniques are intended to serve as methods to control the infectious-source (10):

Numerous potential limitations of these two techniques must be recognized. Neither the efficacy nor reliability of either technique has been adequately evaluated in clinical or laboratory studies.

Masking of patients is only partially effective as was noted in this caution given in 1982 (15):

Because both techniques are heavily dependent on patient behavior, the reliability of both methods and the efficacy of mouth-covering are likely to be highly variable.

With regard to the efficacy of patient masking, a patient's expired airflow takes the path of least resistance, resulting in marginal leakage outward past a mask's face seal. Such airflow patterns deflect at least some of the contagious expired air rather than filtering all of the expired air with its droplet-nuclei load (46,54).

With regard to face-seal leakage of particulate respirators (PRs), respirator specialists, manufacturers, and OSHA consider this class of respirators to permit up to 10% (55,56) to