SARS-CoV-2 disinfection in aqueous solution by UV₂₂₂ from a krypton chlorine excilamp

Abstract

There is an urgent need for evidence-based development and implementation of engineering controls to reduce transmission of SARS-CoV-2, the etiological agent of COVID-19. Ultraviolet (UV) light can inactivate coronaviruses, but the practicality of UV light as an engineering control in public spaces is limited by the hazardous nature of conventional UV lamps, which are Mercury (Hg)-based and emit a peak wavelength (254 nm) that penetrates human skin and is carcinogenic. Recent advances in the development and production of Krypton Chlorine (KrCl) excimer lamps hold promise in this regard, as these emit a shorter peak wavelength (222 nm) and are recently being produced to filter out emission above 240 nm. However, the disinfection kinetics of KrCl UV excimer lamps against SARS-CoV-2 are unknown. Here we provide the first dose response report for SARS-CoV-2 exposed to a commercial filtered KrCl excimer light source emitting primarily 222 nm UV light (UV222), using multiple assays of SARS-CoV-2 viability. Plaque infectivity assays demonstrate the pseudo-first order rate constant of SARS-CoV-2 reduction of infectivity to host cells to be 0.64 cm2/mJ (R2 = 0.95), which equates to a D90 (dose for 1 log10 or 90% inactivation) of 1.6 mJ/cm2. Through RT-qPCR assays targeting the nucleocapsid (N) gene with a short (<100 bp) and long (~1000 bp) amplicon in samples immediately after UV222 exposure, the reduction of ability to amplify indicated an approximately 10% contribution of N gene damage to disinfection kinetics. Through ELISA assay targeting the N protein in samples immediately after UV222 exposure, we found no dose response of the ability to damage the N protein. In both qPCR assays and the ELISA assay of viral outgrowth supernatants collected 3 days after incubation of untreated and UV222 treated SARS-CoV-2, molecular damage rate constants were similar, but lower than disinfection rate constants. These data provide quantitative evidence for UV222 doses required to disinfect SARS-CoV-2 in aqueous solution that can be used to develop further understanding of disinfection in air, and to inform decisions about implementing UV222 for preventing transmission of COVID19.

Mice infected with Mycobacterium tuberculosis are resistant to acute disease caused by secondary infection with SARS-CoV-2

“…A modified version of the plaque assay developed by the Diamond laboratory [40] was used to determine lung viral burdens in challenged animals, the details of which we have reported [41]. Namely, one day prior to the assay start we seeded 12-well with VeroE6 cells and incubated overnight (37˚C 5% CO 2 ) such that each well was confluent by the assay start.…”

Aerosol decontamination and spatial separation using a free-space LED-based UV-C light curtain

“…Coronavirus inactivation was assessed in different studies with different virus strains including common cold coronavirus and SARS-CoV-2. However, all studies show similar outcomes [14][15][16][17][18][19] . Other studies measured higher doses of UV-C radiation needed [20] , which is not surprising as this model uses viral solutions in a petri dish filled with water based buffer solution, resulting in absorption of UV-C light due to the several millimetre thick water layer, an effect otherwise not observed in aerosols of only few micrometres in diameter.…”

Disinfection and decontamination in the context of SARS‐CoV‐2‐specific data

“…Although UV‐C is inclusive of wavelengths spanning 200–280 nm, it has been proposed that particular wavelengths may be more efficacious 104 . Regardless, there is a dose‐responsiveness, and the time to sufficient viral inactivation is dependent on the environment, temperature, distance, and timing for exposure 102,103,105–112 . It is not apparent that any particular SARS‐CoV‐2 strain variant is more or less resistant 110 .…”

“… 104 Regardless, there is a dose‐responsiveness, and the time to sufficient viral inactivation is dependent on the environment, temperature, distance, and timing for exposure. 102 , 103 , 105 , 106 , 107 , 108 , 109 , 110 , 111 , 112 It is not apparent that any particular SARS‐CoV‐2 strain variant is more or less resistant. 110 Differential effects can depend on surface quality and humidity.…”