FDA says new bird flu test results show milk supply is safe

Federal regulators announced Wednesday that additional testing of milk and other dairy products sold in grocery stores shows that pasteurization kills a highly pathogenic strain of bird flu - a finding they say reaffirms their assessment that the nation’s milk supply is safe even as the disease has begun spreading among dairy cattle.

Early results from samples including cottage cheese and sour cream did not detect live bird flu virus, Donald A. Prater, acting director of the Food and Drug Administration’s Center for Food Safety and Applied Nutrition, said in a press call.

“Findings from the U.S. government partners, as well as academic researchers, do not change our assessment of the safety of the milk supply,” Prater said.

Early results last week from an ongoing effort to test 297 samples of retail dairy products from 38 states showed 1 in 5 samples had viral fragments of the H5N1 virus. The presence of genetic fragments of the virus in milk was not unexpected, since the pasteurization process generally does not remove genetic material.

Last week’s findings prompted researchers to perform a more sensitive test to validate that pasteurization kills H5N1 in milk samples. In those tests, they extracted the viral fragments and tried to grow the virus in fertilized eggs - which is known as the gold-standard method for detecting active, infectious viruses. The virus did not grow, confirming that it was not active.

For weeks, key federal agencies have expressed confidence in the safety of the commercial milk supply. The FDA has pointed to data showing that pasteurization inactivates other viruses and that the pasteurization process for eggs - which occurs at a lower temperature than what is used for milk - deactivates the highly pathogenic avian influenza. But experts had called on the agency to back up that claim with new data.

The effort to reassure the public that the milk supply is safe underscores the vast unanswered questions about the virus, which has never before been seen in U.S. dairy cattle. A highly virulent bird flu was first detected in cows in Texas and Kansas in late March, and is known to have spread to 36 total herds and seven other states. On April 1, federal officials announced that a dairy worker in Texas was being treated for H5N1, marking only the second human case in the United States. The worker has recovered.

Since then, federal agencies and experts have been racing to learn more about how the virus is spreading, when it first jumped to dairy cows and how prevalent H5N1 is in herds. Until this week, testing for the bird flu in dairy herds was voluntary, hindering the country’s ability to assess the virus’s spread.

“In some ways, we’re going to have to catch a break and invest a lot of effort and money if we want to drive H5N1 out of the cattle population now that it’s had these months to become established,” said Michael Worobey, a University of Arizona virologist who led a team of scientists who analyzed 239 genetic sequences of the virus. He estimated the bird flu began circulating in dairy cattle some time between November and mid-January.

To date, no H5N1 infections have been reported in beef cattle, and the Agriculture Department has received no reports of symptoms in beef herds, Marissa Perry, spokeswoman for the agency, wrote in an email Tuesday. At a scientific symposium on H5N1 hosted by the Association of State and Territorial Health Officials (ASTHO) last week, a top USDA official said beef cattle are at lower risk because they are not kept in as close quarters as dairy cows, which are often kept in more confined spaces and share food and water sources.

The USDA has expressed confidence that the meat supply is safe but is seeking to verify this through additional studies that include sampling ground beef at retail stores in the states where dairy cattle have tested positive for the H5N1 bird flu.

So far, the outbreak has had minimal impact on international trade. Colombia is the only country known to have put import restrictions on U.S. beef.

Epidemiologists and industry experts worry about the virus potentially spreading to more animals. On some of the earliest affected dairy farms in Texas and Kansas, cats also became sick and died after being fed colostrum and milk from affected cows. The USDA began surveillance of wild pigs several months ago; ongoing testing of domestic swine for influenza would also pick up this bird flu strain, chief veterinary officer Rosemary Sifford said at a symposium last week.

Industry experts say dairy farmers face economic disincentives to test broadly. Farmers don’t want to be known for having an infected herd, which could temporarily decrease milk supply and hurt business.

“It’s pretty clear that there’s a lot of disincentives working,” said Gerald Parker, an associate dean at the College of Veterinary Medicine & Biomedical Sciences at Texas A&M University and a longtime expert on pandemic preparedness. “There’s no clear policy on the way forward. What happens if there is a positive test [in a cow,] and what are the economic impacts to that given herd or the milk supply in a given region?”

Sifford said the USDA is considering compensating milk producers for taking on additional safety measures.

Public health experts say there needs to be more testing of the dairy workforce, including farmworkers, truck drivers and people who work in milk-processing plants and slaughterhouses. Health officials have said broader surveillance of workers is challenging. Some farm owners may be reluctant to work with public health officials because of a lack of trust and the legal status of their workforce, Nirav Shah, principal deputy director at the Centers for Disease Control and Prevention, said during a briefing last week.

Officials say the data they are gathering from this novel outbreak may be changing quickly.

“What we are dealing with today is a bullet train,” Shah said Wednesday at a Council on Foreign Relations event about the agency’s response to the outbreak. “At best, this is a snapshot of that very fast-moving train.”