COVID-19 pandemic lesson learned- critical parameters and research needs for UVC inactivation of viral aerosols

Abstract

The COVID-19 pandemic highlighted public awareness of airborne disease transmission in indoor settings and emphasized the need for reliable air disinfection technologies. This increased awareness will carry in the post-pandemic era along with the ever-emerging SARS-CoV variants, necessitating effective and well-defined protocols, methods, and devices for air disinfection. Ultraviolet (UV)-based air disinfection demonstrated promising results in inactivating viral bioaerosols. However, the reported data diversity on the required UVC doses has hindered determining the best UVC practices and led to confusion among the public and regulators. This article reviews available information on critical parameters influencing the efficacy of a UVC air disinfection system and, consequently, the required dose including the system's components as well as operational and environmental factors. There is a consensus in the literature that the interrelation of humidity and air temperature has a significant impact on the UVC susceptibility, which translate to changing the UVC efficacy of commercialized devices in indoor settings under varying conditions. Sampling and aerosolization techniques reported to have major influence on the result interpretation and it is recommended to use several sampling methods simultaneously to generate comparable and conclusive data. We also considered the safety concerns and the potential safe alternative of UVC, far-UVC. Finally, the gaps in each critical parameter and the future research needs of the field are represented. This paper is the first step to consolidating literature towards developing a standard validation protocol for UVC air disinfection devices which is determined as the one of the research needs.

Keywords: Aerosolization of pathogens; Air sampling methods; Airborne transmission; CDC, centre for disease control and prevention (USA); CMD, count median diameter; DNA, deoxyribonucleic acid; DSB, double strand break; Far-UVC; Far-UVC, ultraviolet irradiation in the ‘far’ range of 200–230 nm; GTC, growth tube collectors; LED, light emitting diode; LPUV, low-pressure ultraviolet lamp; NIOSH, national institute for occupational safety and health; PBS, phosphate buffered saline; PRRS, porcine reproductive and respiratory syndrome; Particle size distribution; REL, recommended exposure limit; RH, relative humidity; RNA, ribonucleic acid; ROS, reactive oxygen species; SARS-CoV-2, severe acute respiratory syndrome coronavirus-2; SSB, single strand break; Suspending media; UV, ultraviolet irradiation; UV-LED, light emitting diode in the ultraviolet range; UVC, ultraviolet irradiation in the ‘C’, or germicidal, spectrum from 200 to 290 nm; UVGI, ultraviolet germicidal irradiation; Viral UVC susceptibility; dsDNA, double-stranded deoxyribonucleic acid; ssRNA, single-stranded ribonucleic acid.