The Food and Drug Administration (FDA) has announced the detection of genetic fragments from the highly-pathogenic avian influenza virus H5N1 in the pasteurized, commercial milk supply. This finding is based on quantitative polymerase chain reaction (qPCR) testing, which detects the presence of viral genetic material but cannot distinguish between live and infectious viral particles or remnants of dead ones killed by the pasteurization process.
Further testing is ongoing to determine if viable, infectious H5N1 can be identified in milk samples. The FDA continues to believe that the milk supply is safe, emphasizing that pasteurization has been proven effective in inactivating bacteria and viruses in milk, including influenza viruses.
H5N1 has recently made a significant jump to US dairy cows, with confirmed cases in multiple herds across eight states. The unexpected spread to bovines has raised concerns about the virus potentially evolving to infect mammals more efficiently, increasing the risk of transmission to humans.
Despite these concerns, federal agencies remain confident that the virus poses little to no risk to the safety of the milk supply. They maintain that pasteurization effectively inactivates the virus, as demonstrated by studies on egg pasteurization, which uses lower temperatures than milk pasteurization.
The FDA, along with the Centers for Disease Control and Prevention (CDC) and the US Department of Agriculture, are continuing their investigations into potential risks, including assessing the effectiveness of pasteurization against this specific strain of H5N1.
While pasteurization is generally expected to kill the virus, it is not a complete sterilization process. As such, the FDA conducted qPCR tests and anticipated finding some genetic fragments in pasteurized milk due to the detection of the virus in raw milk.
The FDA did not provide details on the number of samples tested, the collection locations, or the level of viral genetic material present. They are currently assessing whether egg inoculation tests, considered a gold-standard for determining viral viability, can identify any infectious virus particles.
The FDA will release the results of these tests and others in the coming days or weeks. They emphasize the importance of sharing actionable information and are closely monitoring emergency department and flu testing data for any unusual trends that could indicate the spread of H5N1 to humans. To date, no such trends or activity have been observed.
