Institutional Tuberculosis Transmission. Controlled Trial of Upper Room Ultraviolet Air Disinfection: A Basis for New Dosing Guidelines

Matsie Mphaphlele, Ashwin S. Dharmadhikari, Paul A. Jensen, Stephen N. Rudnick, Tobias H. van Reenen, Marcello A. Pagano, Wilhelm Leuschner, Tim A. Sears, Sonya P. Milonova, Martie van der Walt, Anton C. Stoltz, Karin Weyer, Edward A. Nardell

Transmission is driving the global TB epidemic, especially in congregate settings. Worldwide, natural ventilation is the most common means of air disinfection, but it is inherently unreliable, and of limited use in cold climates. Upper room germicidal UV air disinfection with air mixing has been shown to be highly effective, but improved evidence-based dosing guidelines are needed. 1) To test the efficacy of upper room germicidal air disinfection with air mixing to reduce tuberculosis transmission under real hospital conditions; and, 2) to define the application parameters responsible as a basis for proposed new dosing guidelines. Over an exposure period of 7 months, 90 guinea pigs breathed only untreated exhaust ward air, and another 90 guinea pigs breathed only air from the same 6-bed tuberculosis ward on alternate days when upper room germicidal air disinfection was turned on throughout the ward. The tuberculin skin test conversion rates ( > 6 mm) of the two chambers were compared. The hazard ratio for guinea pigs in the control chamber converting their skin test to positive was 4.9 (CI.95: 2.8, 8.6); an efficacy of approximately 80%. Upper room germicidal ultraviolet air disinfection with air mixing was highly effective in reducing tuberculosis transmission under hospital conditions. These data support using either a total fixture output (rather than electrical or UV lamp wattage) of 15-20 mW/m3 total room volume, or an average whole room ultraviolet irradiance (fluence rate) of 5-7 μW/cm2, calculated by a lighting computer assisted design program modified for ultraviolet use.