Quantitative Microbial Risk Assessment for Quantification of the Effects of Ultraviolet Germicidal Irradiation on Covid-19 Transmission

Quantitative microbial risk assessment (QMRA) is presented as a tool for evaluation of the effectiveness of ultraviolet germicidal irradiation (UVGI) systems for disinfection of indoor air. The QMRA is developed in the context of UVGI system implementation for control of SARS-CoV-2 infection and comprises sub-models to address problem formulation, exposure assessment, and a health effects assessment, all of which provide input to a risk characterization sub-model. The model simulations indicate that steady-state concentrations of airborne, infective pathogens are approached within 1 hour or less in most circumstances and that the majority of change in the risk of disease transmission takes place within the first two hours of exposure. The risk of disease transmission is strongly influenced by the rate of pathogen emission by an infected individual, the output power of UVGI fixtures and their configuration, as well as the characteristics of the heating, ventilation, and air conditioning (HVAC) system. The QMRA framework provides a quantitative link between UVGI/HVAC system characteristics and changes in the risk of disease transmission. The framework can be adapted to other airborne pathogens and provides a rational basis for design, testing, and validation of UVGI systems.