Kinetics And Monte Carlo Simulation of UV Disinfection B. Subtilis Spores And SARS-CoV-2 In Dried Saliva Droplets

Abstract Surfaces can be contaminated by droplets produced coughing or sneezing. In this short, exploratory work, UV disinfection data from B. subtilis spores in dried saliva droplets were fitted to a first-order model. The model has a disinfection rate constant for single organisms, and a smaller one for aggregates (R2 ≥ 0.97). Changes in the fraction of organisms in aggregates (β) alone could account for the effects of different sized droplets in the experimental work. Since a wide spectrum of droplet sizes can be produced and some of the rate constants were uncertain, Monte Carlo simulation was used estimate the UV inactivation performance in dried saliva droplets in a range of conditions. Using conservative lognormal distribution for β, the model was applied to the UV disinfection of SARS-CoV-2 in dried droplets. It was shown that one-log reduction of SARS-CoV-2 was very likely (p>99.9%) and two-log reduction was probable (p=75%) at a dose of 60 mJ/cm2. Aggregates tend to be variable and limit the log reductions that can be achieved at high UV doses.