Abstract
Background: The COVID-19 pandemic urges for cheap, reliable, and rapid technologies for disinfection and decontamination. One frequently proposed method is ultraviolet (UV)-C irradiation. UV-C doses necessary to achieve inactivation of high-titre SARS-CoV-2 are poorly defined.Aim: We investigated whether short exposure of SARS-CoV-2 to UV-C irradiation sufficiently reduces viral infectivity and doses necessary to achieve an at least 6-log reduction in viral titres.Methods: Using a box and two handheld systems designed to decontaminate objects and surfaces, we evaluated the efficacy of 254 nm UV-C treatment to inactivate surface dried high-titre SARS-CoV-2.Results: Drying for 2 hours did not have a major impact on the infectivity of SARS-CoV-2, indicating that exhaled virus in droplets or aerosols stays infectious on surfaces for at least a certain amount of time. Short exposure of high titre surface dried virus (3–5*10^6 IU/ml) with UV-C light (16 mJ/cm2) resulted in a total inactivation of SARS-CoV-2. Dose-dependency experiments revealed that 3.5 mJ/cm2 were still effective to achieve a > 6-log reduction in viral titres, whereas 1.75 mJ/cm2 lowered infectivity only by one order of magnitude.Conclusions: SARS-CoV-2 is rapidly inactivated by relatively low doses of UV-C irradiation and the relationship between UV-C dose and log-viral titre reduction of surface residing SARS-CoV-2 is nonlinear. Our findings emphasize that it is necessary to assure sufficient and complete exposure of all relevant areas by integrated UV-C doses of at least 3.5 mJ/cm2 at 254 nm. Altogether, UV-C treatment is an effective non-chemical option to decontaminate surfaces from high-titre infectious SARS-CoV-2.
Highlights
The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has spread globally since January 2020 and there is an urgent need for rapid, highly efficient, environmentally friendly, and non-chemical disinfection procedures
We investigated whether short exposure of SARS-CoV-2 to UV-C
Caco-2 cells were cultured at 37 °C with 5% CO2 in Dulbecco›s Modified Eagle Medium (DMEM) containing 10% fetal calf serum (FCS), with 2 mM l-glutamine, 100 μg/ml penicillin-streptomycin and 1% non-essential amino acids (NEAA)
Summary
The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has spread globally since January 2020 and there is an urgent need for rapid, highly efficient, environmentally friendly, and non-chemical disinfection procedures. Other studies used innovative 222 nm or 280 nm UV-C light-emitting diode (LED) technologies [8,9] which are not yet implemented in most established 254 nm UV-C-based decontamination devices and needed relatively high doses of UV-C irradiation for inactivation Another recent study by Storm et al established 254 nm UV-C dose-dependency inactivation kinetics of SARS-CoV-2 and reported doses necessary for complete sterilisation of dry and wet virus preparations between 4 s and 9 s at 0.85 mW/cm in a test box [13]. While these data are promising, a limitation of the study design was the use of a test box and relatively low viral titres which allowed for only 2- to 3- log titre reductions by the treatment. UV-C treatment is an effective nonchemical option to decontaminate surfaces from hightitre infectious SARS-CoV-2
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