Efficacy of single pass UVC air treatment for the inactivation of coronavirus, MS2 coliphage and Staphylococcus aureus bioaerosols

• Published in: Journal of aerosol science Vol. 164; p. 106003
• Main Authors: Snelling, William J., Afkhami, Arsalan, Turkington, Hannah L., Carlisle, Claire, Cosby, S. Louise, Hamilton, Jeremy W.J., Ternan, Nigel G., Dunlop, Patrick S.M.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.08.2022; The Authors. Published by Elsevier Ltd
• Subjects: Air sterilisation; Air treatment; MS2; PTFE; SARS-CoV-2; UVC; Air treatment; Air sterilisation; SARS-CoV-2; UVC; MS2; PTFE
• ISSN: 0021-8502; 1879-1964; 0021-8502
• DOI: 10.1016/j.jaerosci.2022.106003

There is strong evidence that SARS-CoV-2 is spread predominantly by airborne transmission, with high viral loads released into the air as respiratory droplets and aerosols from the infected subject. The spread and persistence of SARS-CoV-2 in diverse indoor environments reinforces the urgent need to supplement distancing and PPE based approaches with effective engineering measures for microbial decontamination – thereby addressing the significant risk posed by aerosols. We hypothesized that a portable, single-pass UVC air treatment device (air flow 1254 L/min) could effectively inactivate bioaerosols containing bacterial and viral indicator organisms, and coronavirus without reliance on filtration technology, at reasonable scale. Robust experiments demonstrated UVC dose dependent inactivation of Staphylococcus aureus (UV rate constant (k) = 0.098 m2/J) and bacteriophage MS2, with up to 6-log MS2 reduction achieved in a single pass through the system (k = 0.119 m2/J). The inclusion of a PTFE diffuse reflector increased the effective UVC dose by up to 34% in comparison to a standard Al foil reflector (with identical lamp output), resulting in significant additional pathogen inactivation (1-log S. aureus and MS2, p < 0.001). Complete inactivation of bovine coronavirus bioaerosols was demonstrated through tissue culture infectivity (2.4-log reduction) and RT-qPCR analysis – confirming single pass UVC treatment to effectively deactivate coronavirus to the limit of detection of the culture-based method. Scenario-based modelling was used to investigate the reduction in risk of airborne person-to-person transmission based upon a single infected subject within the small room. Use of the system providing 5 air changes per hour was shown to significantly reduce airborne viral load and maintain low numbers of RNA copies when the infected subject remained in the room, reducing the risk of airborne pathogen transmission to other room users. We conclude that the application of single-pass UVC systems (without reliance on HEPA filtration) could play a critical role in reducing the risk of airborne pathogen transfer, including SARS-CoV2, in locations where adequate fresh air ventilation cannot be implemented. [Display omitted] •Single pass UVC air treatment effectively inactivated coronavirus bioaerosols.•PTFE liners increased irradiance by up to 34% vs standard Al reflectors.•The increased irradiance resulted in an additional 1-log inactivation of pathogens.•Scenario based modelling predicted a significant reduction (82%) in airborne viral load in real environments.