Evaluation of Far Ultraviolet-C Light for Decontamination of Organisms in Whole Milk and Chicken Manure.

Background: The dissemination of highly pathogenic avian influenza (HPAI) A(H5N1) in US poultry and dairy cows poses a public health threat. Farm workers caring for infected animals are at risk to acquire infections due to exposure to contaminated milk or poultry feces and secretions. Far ultraviolet-C (UV-C) light could provide continuous decontamination of surfaces and air in agricultural settings, but efficacy against organisms in whole milk or chicken manure is unclear.

Methods: We examined the efficacy of far UV-C light against bacteriophage MS2 and methicillin-resistant Staphylococcus aureus (MRSA) in phosphate-buffered saline (PBS), 5% fetal calf serum, whole milk, or 5%, 10%, and 25% chicken manure, both in liquid suspension and dried on surfaces. We also compared the efficacy of 300 mJ/cm² doses of far UV-C and 254-nm UV-C light against the test organisms in liquid droplets or droplets dried on surfaces.

Results: For both test organisms, far UV-C achieved significantly smaller log₁₀ reductions in whole milk and in chicken manure suspensions than in PBS or 5% fetal calf serum, both in liquid suspension and when dried on surfaces (P<0.0001). In whole milk, average reductions of both organisms with all doses were ≤1.2 log₁₀ in liquid suspensions and ≤2.4 log₁₀ when dried on surfaces. We found 254-nm UV-C was significantly more effective in reducing MRSA and MS2 dried on surfaces in whole milk or in 10% chicken manure (P≤0.02) but not in liquid droplets (P>0.05) except 5% chicken manure (P<0.001).

Conclusions: Our results suggest that in the absence of prior cleaning and disinfection far UV-C and 254-nm UV-C light technologies may have limited efficacy as an adjunctive method to reduce the risk for transmission of HPAI from surfaces in high-risk settings on farms.