In December 2023, a shopper selects milk at a grocery store in San Anselmo, California.
U.S. health agencies are launching comprehensive investigations into the potential risks of H5N1 bird flu among dairy workers and milk products. The CDC, in collaboration with Michigan, begins a pivotal study to determine if workers exposed to infected cattle have contracted the virus. Concurrently, the FDA is evaluating flash pasteurization's effectiveness following concerns about its ability to eradicate all virus traces in milk.
These initiatives are part of a broader research endeavor announced by federal agencies to comprehend the dynamics of H5N1 bird flu, which recently transmitted from birds to dairy cattle earlier this year. The USDA confirms over 120 herds across 12 states have tested positive for this highly contagious infection, primarily spreading through direct contact with raw milk.
"We know that milk is a key vehicle for transmission," stated Dr. Eric Deeble, USDA's acting senior adviser for avian influenza. Initially, cattle movement drove the infection's spread, but since April's interstate testing mandate by USDA, the virus now travels between farms via shared equipment and workers, according to a recent MDARD study.
MDARD Director Dr. Tim Boring emphasized the high viral loads in milk pose significant transmission risks, though the exact mechanisms of human infection—whether through direct contact, contaminated clothing, or skin—are still unclear.
Farmers have hesitated to permit extensive herd testing, while workers, fearful of lost wages, avoid medical examinations even when symptomatic. Michigan's recent offer to subsidize research costs for 20 dairy farms has encouraged participation, supplemented by federal funds.
Recently, the CDC announced a collaboration with Michigan's Health and Human Services to analyze farm workers' blood for H5N1 antibodies, aiming to detect asymptomatic infections, as Dr. Demetre Daskalakis, CDC's director of Immunization and Respiratory Diseases, explained.
The FDA has also initiated a new round of dairy product sampling, including raw milk cheeses and ice cream, to address gaps found in earlier tests where one in five samples showed viral traces. Subsequent tests confirmed these traces were inactive and posed no health risks once milk is pasteurized.
However, recent studies published in the New England Journal of Medicine have raised concerns. They indicate that while flash pasteurization reduces infectious virus levels in milk significantly, it may not eliminate all traces, prompting calls for further research. Dr. Don Prater, FDA's acting director for Food Safety and Applied Nutrition, stressed the need for comprehensive studies on virus persistence in cheese and pooled testing of raw milk samples.
Prater refrained from specifying timelines for these studies but expressed hopes for timely results. These investigations aim to safeguard public health by ensuring dairy products remain safe for consumption amid the ongoing challenges posed by H5N1 bird flu.
