Traces of bird flu have made it into store-bought milk in New England, but at very low levels - The Boston Globe

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Each milk sample was pasteurized, a heating process designed to kill pathogens that leaves behind inactive viral particles. It is rare for humans to become infected with H5N1.

In some ways, the preliminary results are reassuring, some public health experts said. More than three-quarters of the samples were processed in dairy plants in New England, and none produced a conclusively positive result. The one positive sample was processed in a state with a known outbreak of bird flu among its dairy cows.

"It's remarkable that New England is still clear of cases [on dairy farms] given how widespread H5N1 has become, but it's likely a matter of time before we are exposed," said Pardis Sabeti, the Broad Institute geneticist whose lab conducted the tests. "There is a unique moment of opportunity to keep our farms protected and thriving through testing and surveillance."

The goal of the Broad's tests was to determine if the virus was present on New England farms, which would place agricultural workers and those who consume locally bought unpasteurized milk products at risk of infection.

The results provide the first known evidence that the virus — at least in an inactive form — is now present in food products consumed in New England. They also underscore the scope and persistence of the threat and highlight the changing nature of milk production in New England and nationally.

Last month, the FDA conducted its own testing of store-bought milk, purchasing 297 dairy samples including milk from 38 states. It found viral fragments in 20 percent of the samples. But the agency did not disclose where the milk was purchased. In a separate study, researchers from Ohio State and the University of Illinois purchased 150 samples in 10 states. More than a third tested positive.

The more the virus spreads, the greater the likelihood it will develop genetic changes that allow it to more easily infect mammals, including humans.

To find out if H5N1 was present in local supermarkets, Globe staffers fanned out across Massachusetts, Rhode Island, and New Hampshire earlier this week, heading for the dairy sections of Star Market, Stop & Shop, Cumberland Farms, Whole Foods, Traders Joe's, Shaws, Target, and a wide array of other stores.

They delivered the milk in coolers to Sabeti's lab in Cambridge's Kendall Square. After using specialized machines to extract any genetic material present and reproduce it 1 billion times, members of her lab then added fluorescent chemical particles that rendered any fragments of the H5N1 virus visible to a specialized camera, explained Elyse Stachler, a research scientist who led the genetic testing. Each sample underwent testing twice before technicians rendered their verdict. Some underwent a third test that was even more stringent.

Many experts worry that the virus may be far more widespread on the nation's dairy farms than currently known. Federal regulations now require H5N1 testing for cows slated to be transported across state lines. But otherwise most testing remains voluntary. To date, only about 30 people have been tested for the virus nationwide by state and local officials, federal officials said recently.

"The way that they're trying to find the virus on farms is woefully inadequate," said Jennifer Nuzzo, professor of epidemiology and director of the Pandemic Center at the Brown University School of Public Health. "Our current testing scheme is dangerous. We remain concerned about the potential for the virus to evolve, to gain the ability to infect humans more easily."

Dr. Catherine M. Brown, state epidemiologist and state public health veterinarian for the Massachusetts Department of Public Health, said the discovery of viral fragments in the milk does not surprise her given the results of previous federal testing. Since the CDC has deemed the virus low risk to human health, monitoring its spread remains a "collaborative effort," that is still being led on the state level by the Massachusetts Department of Agricultural Resources. To date, there have been no confirmed cases of H5N1 in the state in cows or humans.

The state's milk remains safe. The exception, she notes, is raw milk.

"Raw milk is a concern every single day, separate from H5N1, because it can and frequently does contain bacterial pathogens that cause severe disease and even occasionally death in people," she said.

Since arriving in the United States in late 2021, carried by migratory birds, the H5N1 virus has led to the deaths of tens of millions of birds and developed new mutations that have already allowed it to jump to mammals. In New England, scores of sea ducks, loons, and seagulls have littered the beaches along the North Shore in recent months, washing up in Nahant Beach, Salisbury, Newbury, Newburyport, Plum Island, and Manchester-by-the-Sea.