Inactivation Challenges of SARS-CoV-2 on Surfaces in the Built Environment by Irradiation from Pulse Xenon, 275 nm Light-Emitting-Diode, and Far-Ultraviolet Sources

Motivated by the COVID-19 pandemic, laboratory tests were conducted to evaluate ultraviolet-C (UVC) radiation-emitting devices that are potentially capable of inactivating severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) on surfaces common to the built environment. In this study, we evaluated the efficacy of three UVC radiation-emitting devices: a pulsed xenon light, a 275 nm LED, and a 222 nm far-UVC light. Experiments were conducted using virus-containing droplets in either tissue culture media or simulated saliva inoculated onto the materials. UVC radiation was significantly more effective in the inactivation of SARS-CoV-2 on hard nonporous surfaces versus porous surfaces; more effective in wet droplets versus dried droplets, while the inoculum type had less of an impact. These observations are partially supported by UVC absorption measurements of the inoculum, which indicated a higher UVC absorption for simulated saliva versus tissue culture media. Absorption spectra for dried inoculum were identical between 260 and 280 nm, with higher absorbances for tissue culture media versus simulated saliva for shorter wavelengths. The observed reduction in efficacy from laboratory conditions (wet, tissue culture media in, e.g., Petri dishes) to more realistic conditions (dried, simulated saliva droplets) indicates that the implementation of UVC radiation leading to an effective risk reduction remains challenging for surface treatment.