UV-induced inactivation rates for airborne Mycobacterium bovis BCG

Engineering ultraviolet irradiation systems as a control against infectious airborne diseases requires a knowledge of intrinsic ultraviolet (UV) inactivation rates of airborne bacteria. Ultraviolet inactivation rates for airborne Mycobacterium bovis bacillus Calmette-Guérin (BCG) were determined at 50% and 95% relative humidity (RH) in a 0.8 m3 bioaerosol reactor. Ultraviolet inactivation response of waterborne M. bovis BCG pure cultures was also determined. At 50% RH the airborne UV inactivation rates observed were two times greater than those observed in saturated air (RH = 95%), and rates at 95% RH were similar to those observed in otherwise identical cultures suspended in water. Intrinsic UV inactivation rates for M. bovis BCG were statistically similar to rates observed for Mycobacterium parafortuitum at 50% and 95% RH, indicating that M. parafortuitum is a valid surrogate for studying airborne UV responses of M. bovis BCG and Mycobacterium tuberculosis. Results also confirm that UV inactivation responses for bacteria suspended in water cannot be used to estimate UV dose response in unsaturated air.