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):
A simple but important source-control technique is for infectious patients to cover all coughs and sneezes with a tissue, thus containing most liquid drops and droplets before evaporation can occur [53]. A patient's use of a properly fitted surgical mask or disposable, valveless particulate respirator (PR) (see section II.D.2.c) also may reduce the spread of infectious particles. However, since the device would need to be worn constantly for the protection of others, it would be practical in only very limited circumstances (e.g., when a patient is being transported within a medical facility or between facilities).
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):
Masking a coughing patient when someone enters his room may reduce the addition of bacilli to the air; this will not completely eliminate the hazard of transmission, however, since the room air would already be contaminated if the patient had been coughing without covering his mouth.
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
