Effective ultraviolet C light disinfection of respirators demonstrated in challenges with Geobacillus stearothermophilus spores and SARS-CoV-2 virus

BACKGROUND: The global COVID-19 pandemic, accompanied by spikes in the number of patients in hospitals, required substantial amounts of respiratory protective devices (respirators), thereby causing shortages. Disinfection of used respirators by applying ultraviolet C (UVC) light may enable safe reuse, reducing shortages. AIM: To determine whether UVC disinfection is applicable to enable repeated safe reuse of respirators. METHODS: The UVC chamber, equipped with low-pressure mercury discharge lamps emitting at 254 nm, was used to determine the sporicidal and virucidal effects. Respirators challenged with spores and viruses were exposed to various UVC energy levels. Deactivation of the biological agents was studied as well as UVC effects on particle filtration properties and respirator fit. FINDINGS: A 5 log(10) reduction of G. thermophilus spore viability by a UVC dose of 1.1 J/cm(2) was observed. By simulating spores present in the middle of the respirators, a 5 log(10) reduction was achieved at a UVC dose of 10 J/cm(2). SARS-CoV-2 viruses were inactivated by 4 log(10) upon exposure to 19.5 mJ/cm(2) UVC. In case UVC must be transmitted through all layers of the respirators to reach the spores and virus, a reduction of >5 log(10) was achieved using a UVC dose of 10 J/cm(2). Exposure to a six-times higher UVC dose did not significantly affect the integrity of the fit nor aerosol filtering capacity of the respirator. CONCLUSION: UVC was shown to be a mild and effective way of respirator disinfection allowing for reuse of the UVC-treated respirators.