Germicidal UV for the Control of Airborne Bacteria and Viruses: A Critical Review of Efficacy and the Production of Secondary Pollutants

Germicidal ultraviolet radiation (GUV) has long been a promising solution to indoor transmission of airborne diseases, but has not yet seen widespread adoption. This review addresses: the efficacy of GUV in inactivating airborne pathogens in laboratory experiments; the effect of pathogen structural characteristics and taxonomy on GUV susceptibility; and evidence that GUV produces airborne pollutants, all of which are key challenges to the widespread adoption of this technology. With respect to the first objective, the median susceptibility constants Z for viruses and bacteria across all wavelengths were 2.2 cm2 mJ–1 and 3.5 cm2 mJ–1, respectively. GUV using 222 nm radiation has higher exposure thresholds than 254 nm, which permits a higher dose and is therefore likely more efficacious in practice. For the second objective, there is a difference in efficacy between bacterial families, dependent on cell wall characteristics, but there are not enough studies on viruses to determine whether their structural properties influence UV susceptibility. For the third objective, both 222 and 254 nm can generate air pollutants that differ in composition, quantity, and production pathways, and under some conditions can be at harmful levels. However, operating the devices at fluence rates within guideline limits and with adequate ventilation appears to greatly mitigate the risk of pollutant accumulation. The potential for human harm from these pollutants, however, is still concerning and requires a combination of adequate ventilation, consistent monitoring, and intelligent building systems to completely safeguard against human exposure to high levels of pollutants over prolonged periods. Exposure to high concentrations of pollutants leads to morbidity, and so confidence in the ability to prevent pollutant accumulation must be absolute prior to the implementation of GUV.