Estimation of Tuberculosis Risk and Incidence under Upper Room Ultraviolet Germicidal Irradiation in a Waiting Room in a Hypothetical Scenario

Abstract

Environmental control measures (ventilation, high-efficiency particulate air filtration, and upper room ultraviolet germicidal irradiation [UVGI]) are recommended to effectively control tuberculosis (TB) transmission from unsuspected TB patients in high-risk settings, but the effectiveness of their use is not often clear. This study presents a simulation model for a hypothetical hospital waiting room, in which the number of susceptible immunocompetent 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 (annual number of TB patients = 50), and used the model to evaluate the reduction 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 evaluating the effect of upper room UVGI. Upper room UVGI reduced TB risk by 1.6-fold at 3 microW/cm2 UV irradiance in the upper room in the low TB risk setting and by 4.1-fold at 15 microW/cm2 UV irradiance in the upper room in the 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 microW/cm2 and to 0.6 infections per year at 15 microW/cm2 in our hypothetical high-risk settings. The effect of upper room UVGI was sensitive to both vertical air velocity (air mixing) and UV irradiance level. Results from partitioning variability indicate that most variability of TB transmission risk came from waiting time in our hypothetical hospital.

Prevention of nosocomial transmission of extensively drug-resistant tuberculosis in rural South African district hospitals: an epidemiological modelling study

“…A mechanical ventilation system in this ward was estimated to produce 402 m 3 /h (range 330-1,209), with high-efficiency particulate air (HEPA) supplementation further increasing effective ventilation by a factor of 3.37 and ultraviolet germicidal irradiation (UVGI) supplementation increasing effective ventilation by a factor of 10.31 above the unsupplemented system [8,[61][62][63][64][65]. Upper-room UVGI in a waiting area alone was not simulated because of the absence of data that could be extrapolated to the simulated hospital [66]. Triangular distributions were constructed for sampling, according to the mean and range of the ventilation rate.…”

Use of a mathematical model to estimate tuberculosis transmission risk in an Internet café

“…The Wells-Riley mathematical model has been used to estimate airborne TB infection risk in an enclosed space [7][8][9][10]. The spread of TB infection in an Internet café used by an unspecified number of people is not clear.…”

Computational fluid dynamics modelling and optimisation of an upper-room ultraviolet germicidal irradiation system in a naturally ventilated hospital ward

“…Energy data on UV systems is limited, but a small number of studies have carried out calculations to explore benefits. Ko et al [8] consider the effectiveness of UV against TB transmission in a waiting room and calculate that UV may be less expensive than increased ventilation by between 3 and 13 times [46]. We recently conducted a modelling study [9] that suggested that installation of UV can achieve reductions in airborne risk comparable to or better than increasing the ventilation rate from 3 to 6 ACH at 11-55% of the energy cost, depending on the scenario.…”

“…However there is increasing awareness of the relationship between ventilation rate and energy consumption; up to 44% of energy in UK hospitals is thought to be consumed by ventilation and space heating [7]. Studies have suggested that air cleaning technologies may offer the potential to reduce airborne infection risk without the energy costs associated with higher ventilation rates [8,9].…”