Estimation of tuberculosis risk and incidence under upper room ultravioletgermicidal irradiation in a waiting room in a hypothetical scenario

Environmental control measures (ventilation, high-efficiency particulate ai r filtration, and upper room ultraviolet germicidal irradiation [UVGI]) are recommended to effectively control tuberculosis (TB) transmission from uns uspected TB patients in high-risk settings, but the effectiveness of their use is not often clear. This study presents a simulation model for a hypoth etical hospital waiting room, in which the number of susceptible immunocomp etent people in the waiting room follows a Poisson distribution (M = 5) in either low (annual number of TB patients = 5) or high TB risk settings (ann ual number of TB patients = 50), and used the model to evaluate the reducti on of TB transmission risk by upper room UVGI. An exponential dose-response model was used for TB transmission and a two-zone model was used for evalu ating the effect of tipper room UVGI. Upper room UVGI reduced TB risk by 1. 6-fold at 3 muW/cm(2) UV irradiance in the upper room in the low TB risk se tting and by 4.1-fold at 15 muW/cm(2) UV irradiance in the upper room in th e high TB risk setting. Use of upper room UVGI also reduced the mean annual new infection rate from 2.2 to 1.3 infections per year at 3 muW/cm(2) and to 0.6 infections per year at 15 muW/cm(2) in our hypothetical high-risk se ttings. The effect of upper room UVGI was sensitive to both vertical air ve locity (air mixing) and UV irradiance level. Results from partitioning vari ability indicate that most variability of TB transmission risk came from wa iting time in our hypothetical hospital.