Effects of ultraviolet germicidal irradiation of room air on airborne bacteria and mycobacteria.

As a result of the recent resurgence in tuberculosis (TB), there has been renewed interest inengineering controls to reduce the spread of TB and other airborne infectious diseases in highrisk settings. This paper presents the results of experimental studies evaluating the efficacy ofultraviolet germicidal irradiation (UVGI) of room air in reducing the concentration of viableairborne bacteria. Bacterial particles (Bacillus subtilis spores and Mycobacteriumparafortuitum) were continuously generated in a 90m room. The room was equipped withgermicidal lamps, a computer-controlled ventilation system, and temperature and relativehumidity controls. Air samples were collected using impingers at 11 locations within theroom. Concentrations were quantified using standard culturing and colony plate counts. Theeffectiveness of the control technique was determined by comparing concentrations ofculturable airborne bacteria with and without the control in operation. The germicidal lampsthat were evaluated reduced the room-average concentration of culturable airborne bacteria,typically by 4095% depending on the microorganism used in the experiments, relative toconcentrations with no lamps in use.