Inactivation of Avian Influenza A(H5N1) virus in raw milk at 63°C and 72°C
Molecular testing identified HPAI A(H5N1) genetic material in about 20% of samples from retail pasteurized milk products. However, researchers have been unable to culture the virus from these samples. In a recent study, scientists from the National Institute of Allergy and Infectious Diseases (NIAID) assessed the stability of the HPAI A(H5N1) virus in raw milk at 63°C and 72°C, the temperatures commonly used in commercial pasteurization. Their findings were published in a letter in the New England Journal of Medicine. Heating milk to 63°C resulted in a tenfold decrease in H5N1 levels after 2.5 minutes, indicating that the standard bulk pasteurization process of 30 minutes at 63°C provides a significant safety margin. At 72°C, virus levels decreased fourfold within 5 seconds, but very small amounts of infectious virus were detected after 20 seconds in one of three samples.
These results suggest that a small but detectable quantity of H5N1 virus may remain infectious in milk after 15 seconds at 72°C if the initial virus levels are high. The authors noted that these findings are based on experimental laboratory conditions and may not accurately reflect large-scale industrial pasteurization processes.
