Detection of A(H5N1) influenza virus nucleic acid in retail pasteurized milk

The detection of A(H5N1) clade 2.3.4.4b influenza A virus (IAV) in dairy cattle in the U.S. presents a significant threat to the economy, animal well-being, and public health. Preliminary reports of a high viral load in milk from infected cattle sparked concern regarding the safety of the commercial milk supply in the U.S.1–3 Through a convenience sampling of pasteurized milk purchased from retail stores across the United States, we detected A(H5N1) viral nucleic acid in 36.3% of samples. Viral sequencing confirmed the presence of genetic material from A(H5N1) clade 2.3.4.4b influenza A viruses. Despite the detection of relatively high levels of viral RNA, no evidence of viable virus was found following inoculation of MDCK cells, embryonated chicken eggs, or mice with positive retail milk samples. This study highlights the wider distribution of states affected by the virus than suggested by official reports, provides supporting evidence for the efficacy of pasteurization, and suggests the value of retail milk as a means to monitor continued viral evolution.