Reducing Potentially Infectious Bioaerosols during Sputum Induction

Interest in the nosocomial transmission of tuberculosis was reawakened in the late 1980s and early 1990s when more than a dozen institutions in the United States experienced major outbreaks. Subsequent recommendations to strengthen environmental controls emphasized proper ventilation. Ultraviolet germicidal irradiation (UVGI), although relatively inexpensive, was considered an adjunct measure.1,2 Simultaneous implementation of administrative, personal, and environmental control measures resulted in rapid reduction of nosocomial transmission in several institutions.3-6 However, the contribution of the relatively expensive environmental controls7 could not be distinguished from that of other measures implemented at the same time. Experimental studies have demonstrated that UVGI can achieve the equivalent of almost 20 air changes per hour (ACH) in killing airborne bacille Calmette–Guérin,8 can kill airborne Mycobacterium tuberculosis,9 and can prevent transmission of M. tuberculosis to experimental animals.10 Although field studies have documented reduced transmission of other microorganisms,11-13 no such studies have evaluated the efficacy of UVGI to prevent nosocomial transmission of tuberculosis. Therefore, the use of UVGI remains controversial, particularly because there are safety concerns. The importance of cough-inducing procedures in the dissemination of airborne infection such as tuberculosis has been demonstrated experimentally,14 in reports of outbreaks,15 and in epidemiologic studies of respiratory technicians16,17 and pulmonary trainees.18 In 1996, the sputum induction room in our hospital was equipped with a wall-mounted upper air UVGI fixture, and exhaust ventilation providing at least 15 ACH. We conducted this study to evaluate the efficacy of these environmental controls in eliminating potentially infectious aerosols generated by patients undergoing sputum induction.