Robust Evaluation of Ultraviolet-C Sensitivity for SARS-CoV-2 and Surrogate Coronaviruses

Abstract

UV light, more specifically UV-C light at a wavelength of 254 nm, is often used to disinfect surfaces, air, and liquids. In early 2020, at the cusp of the COVID-19 pandemic, UV light was identified as an efficient means of eliminating coronaviruses; however, the variability in published sensitivity data is evidence of the need for experimental rigor to accurately quantify the effectiveness of this technique. In the current study, reliable and reproducible UV techniques have been adopted, including accurate measurement of light intensity, consideration of fluid UV absorbance, and confirmation of uniform dose delivery, including dose verification using an established biological target (T1UV bacteriophage) and a resistant recombinant virus (baculovirus). The experimental results establish the UV sensitivity of SARS-CoV-2, HCoV-229E, HCoV-OC43, and mouse hepatitis virus (MHV) and highlight the potential for surrogate viruses for disinfection studies. All four coronaviruses were found to be easily inactivated by 254 nm irradiation, with UV sensitivities of 1.7, 1.8, 1.7, and 1.2 mJ/cm²/log₁₀ reduction for SARS-CoV-2, HCoV-229E, HCoV-OC43, and MHV, respectively. Similar UV sensitivities for these species demonstrate the capacity for HCoV-OC43, HCoV-229E, and MHV to be considered surrogates for SARS-CoV-2 in UV-inactivation studies, greatly reducing hazards and simplifying procedures for future experimental studies. IMPORTANCE Disinfection of SARS-CoV-2 is of particular importance due to the global COVID-19 pandemic. UV-C irradiation is a compelling disinfection technique because it can be applied to surfaces, air, and water and is commonly used in drinking water and wastewater treatment facilities. UV inactivation depends on the dose received by an organism, regardless of the intensity of the light source or the optical properties of the medium in which it is suspended. The 254 nm irradiation sensitivity was accurately determined using benchmark methodology and a collimated beam apparatus for four coronaviruses (SARS-CoV-2, HCoV-229E, HCoV-OC43, and MHV), a surrogate indicator organism (T1UV), and a resistant recombinant virus (baculovirus vector). Considering the light distribution across the sample surface, the attenuation of light intensity with fluid depth, the optical absorbance of the fluid, and the sample uniformity due to mixing enable accurate measurement of the fundamental inactivation kinetics and UV sensitivity.

Keywords: HCoV-229E; HCoV-OC43; HuCoV 229E; HuCoV OC43; MHV; SARS-CoV-2; T1 bacteriophage; baculovirus vector; collimated beam; coronavirus; disinfection; irradiation; ultraviolet.

FIG 1

Inactivation of SARS-CoV-2 and three surrogate coronaviruses by exposure to UV-C irradiation. Doses are corrected for an adjustment factor for each radiometer. *, 1 replicate no virus detected and 2 replicates at detection limit (HCoV-OC43); point excluded from fitted line. SARS-CoV-2: y = 0.59x + 0.15, R² = 0.99; HCoV-229E: y = 0.56x + 0.12, R² = 0.99; HCoV-OC43: y = 0.59x + 0.07, R² = 0.99; MHV: y = 0.82x + 0.05, R² = 0.99. (a to d) Triplicate irradiations were performed for each dose; all replicates shown on plot. Dashed lines represent detection limits. Arrows represent no virus detected in assay at those doses. (e) Each point represents the mean of triplicate sample irradiation. Error bars represent range of data. Detection limits were 6.22, 5.09, 4.38, and 3.77 log₁₀(N₀/N) for SARS-CoV-2, MHV, HCoV-OC43, and HCoV-229E, respectively.

FIG 2

Verification of collimated beam dose delivery from T1UV bacteriophage. Dose response data generated with collimated beam kits used at both the University of Waterloo and McMaster University, as well as a third collimated beam kit at a reference laboratory (Trojan Technologies). For each collimated beam kit, duplicate irradiations were performed for each dose, and values shown are averages of duplicate plating of each irradiated sample. Doses are corrected for an adjustment factor for each radiometer. All dose-response data fell within the 95th percentile prediction intervals for T1UV, shown as solid lines (6).

FIG 3

Inactivation of baculovirus by exposure to doses of UV-C irradiation. Doses are corrected for an adjustment factor for each radiometer. Duplicate irradiations were performed for each dose and all replicates are shown on the plot; y = 0.036x − 0.06, R² = 0.99.

FIG 4

Absorption spectrum of RNA and DNA, along with measured sensitivity values for three coronaviruses: HCoV-OC43, HCoV-229E, and MHV. All values normalized to 254 nm.