A comprehensive evaluation of ultraviolet irradiation at 254 nm and 222 nm in inactivating human noroviruses on surfaces

Human norovirus (hNoV) presents significant public health challenges due to its low infectious dose and environmental persistence. This study compared the inactivation efficacy of ultraviolet C irradiation at 254 nm (UV 254) and far-UVC radiation at 222 nm (UV 222) against four hNoV strains and two surrogate viruses, Tulane virus (TV) and bacteriophage MS2. A symptom scoring assay was developed to assess hNoV infectivity following microinjection into zebrafish embryos, being used in combination with reverse transcriptase quantitative PCR (RT-qPCR), long-range RT-qPCR, and RNase-treated RT-qPCR. With a general laboratory set-up of viruses being suspended in deionized water droplets in Petri dish, UV 222 was demonstrated with comparable, if not superior, performance in reducing hNoV infectivity and RNA integrity, and was significantly more effective than UV 254 in damaging viral capsids. MS2 exhibited inactivation patterns similar to hNoVs, whereas TV was markedly more resistant to UV 222. The performance of UV 222 was consistent in inactivating hydrated viruses on both stainless steel and porcine skin surfaces. However, the efficacy of UV-222 was substantially more reduced when virus inocula were dried or mixed with simulated vomitus containing high levels of organic matter, compared with UV-254. No evidence of viral adaptation or persistent genomic diversification was detected following repeated sublethal UV exposures. Taken together, UV 222 can be regarded as a promising technology in surface disinfection, especially for hNoV control, meantime keeping safe for human exposure. ImportanceHuman norovirus, the main cause of foodborne illness and non-bacterial gastroenteritis, can be transmitted through human-to-human contact. Indirectly, food or food related surfaces are readily contaminated by hNoV, completing the transmission route. So far, no standard cultivation tool is available for detecting viable hNoV, resulting in the challenges of evaluating inactivation effectiveness of various disinfection technologies, including UV 222 treatments. The significance of our study lays in attempts to quantify hNoV infectivity loss of four strains using zebrafish model during UV 222 and 254 treatments, together with the underlying antiviral mechanisms indicated by three different types of reverse transcription qPCR methods. In addition, the concerns over possible emergence of variant were subdued by genome wide sequencing results after consecutive UV exposures and passaging in vivo zebrafish model. SynopsisUV 222 is recommended to be applied after surface cleaning and ideally on moist surfaces.