A new study led by the National University of Singapore and published in Applied and Environmental Microbiology demonstrated the efficacy of ultraviolet C (UV-C) irradiation for inactivating human norovirus on surfaces, with the researchers calling it a promising, safe technology for surface disinfection.

Different UV-C Wavelengths, Food Contact Surfaces

The researchers compared the inactivation efficacy of UV-C irradiation at 254 nanometers (nm), or UV 254, and far-UV-C radiation at 222 nm (UV 222) against four norovirus Genotype II (GII) strains and two surrogate viruses. A symptom-scoring assay was developed to assess norovirus infectivity following microinjection into zebrafish embryos, being used in combination with reverse transcriptase PCR (RT-qPCR), long-range RT-qPCR, and RNase-treated RT-qPCR.

UV 222 and UV 254 were applied to viruses suspended in deionized water droplets in a petri dish, on stainless steel coupons, or on pig skin. The treatment was also applied to simulated vomitus containing norovirus on the stainless steel and porcine surfaces to assess the impact of organic matter on UV’s efficacy. The treatments were applied at 7 and 70 mJ/cm².

UV Effective Against Norovirus on Clean Surfaces

When the viruses were tested in droplets in petri dishes, UV 222 showed comparable, if not better, efficacy in reducing human norovirus infectivity and RNA integrity and is considerably more efficient in damaging viral capsid protein than UV 254. When the viruses were spiked onto stainless steel surfaces and porcine skin, UV 222 showed comparable inactivation efficacy to UV 254 on hydrated virus inocula. When the viruses were dried on the surfaces or mixed with simulated vomitus, the inactivation efficacy of both UV 222 and UV 254 was markedly reduced, with UV 254 proving more effective than UV 222.

The researchers attributed these findings to the low penetration of UV-C, representing a key limitation of this technology for environmental disinfection. Compared to petri dishes, stainless steel has a rougher surface, and pig skin has natural niches, allowing dried viruses to remain partially shielded from direct UV exposure.

Also notably, the norovirus strains showed strain-specific variability in their response to UV treatments, with GII.2 being the most susceptible and GII.17 the least.

Novel Method for Evaluating Efficacy of Norovirus Inactivation Methods

In addition to identifying the efficacy of UV treatments against norovirus on surfaces, the study is important because it utilized a novel method for measuring the UV treatment’s efficacy—an in vivo zebrafish model for quantifying the loss in norovirus infectivity.

At present, no standard cultivation technique is available for detecting viable human norovirus, making it historically difficult to evaluate the inactivation effectiveness of disinfection technologies. However, the researchers’ zebrafish model successfully enabled precise quantification, providing “a more practical and accessible platform for evaluating the efficacy of inactivation strategies in a quantitative way,” per the study.

Real-World Applications for UV Surface Disinfection

Based on their findings, the researchers believe that the installation of 222-nm UV lights in enclosed foodservice settings, such as cruise ships, and food processing environments can enable real-time, continuous disinfection even during occupancy.

UV 222 presents a safer exposure profile for human skin and eyes than UV 254, per the researchers. UV 222’s demonstrated safety supports its direct application onto high-touch surfaces, or even for hand disinfection.

However, the study did identify a trade-off between safety and efficacy. While UV 222 is safer for human exposure than UV 254, its lower penetration makes it less effective in the presence of organic matter or on rough surfaces.

Therefore, the researchers concluded that UV 222 should be applied after surface cleaning to remove debris and organic matter, and ideally on moist surfaces to maximize its efficacy.

Future Research and Development Needs

Moving forward, the researchers underline the need to develop standards for far-UV-C device performance, dose calibration, and safety to ensure consistent and effective implementation. Additionally, combining UV 222 with chemical sanitizers, photocatalytic coatings, or aerosol treatments less affected by shadowing may further enhance its efficacy and broaden its applicability in real-world settings.