Germicidal efficacy of continuous and pulsed ultraviolet-C radiation on pathogen models and SARS-CoV-2

CoV-2 can survive on surfaces for days. The pressing need for efficient high-touch surface disinfection and sterilization methods has led to a flood of unproven radiation-emitting UV lights and handheld UV devices on the market. Concerns about unproven claims and potentially significant direct and indirect risks these devices may pose to public health, safety, and the environment, have led the FDA and Health Canada to issue technical requirements and warnings to manufacturers, but research-based data on their efficacy has been limited.

To test the germicidal efficacy of UV-C light sources compared to UV-LEDs, we irradiated droplet suspensions of SARS-CoV-2 and several other microbes with market-available UV-LEDs (260 nm, 273 nm, 277 nm, and 280 nm), a UV laminar flow hood lamp (254-nm peak), and a KrCl excimer (222-nm) light source. A range of UV-C dosages were applied to the slides for different durations.

Although the dosage required to have an effect varied from one source to the next, SARS-CoV-2 was equally susceptible to all UV-C sources: 99.99% of the virus in our samples was inactivated.  Our study suggests that the incorporation of UV-C devices emitting at 222 nm for surface decontamination has the advantage of superior germicidal activity without adverse health effects (i.e., tissue penetration and protein damage). This underlines the importance of verifying spectral outputs for manufactured ultraviolet light sources, reporting detailed methodologies for acquiring data on pathogen-specific sensitivities to UV-C light.

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