Pasteurized milk includes remnants of H5N1 bird flu, U.S. officials say

The U.S. Food and Drug Administration says that samples of pasteurized milk havetested positive for remnants of the bird flu virus that has infected dairy cows.

The agency stressed that the material is inactivated and that the findings "do not represent actual virus that may be a risk to consumers." Officials added that they're continuing to study the issue.

"To date, we have seen nothing that would change our assessment that the commercial milk supply is safe," the FDA said in a statement on Tuesday.

The announcement comes nearly a month after an avian influenza virus that has sickened millions of wild and commercial birds in recent years was detected in dairy cows in at least eight states. The Agriculture Department (USDA)says 33 herds have been affected to date.

FDA officials didn't indicate how many samples they tested or where they were obtained. The agency has been evaluating milk during processing and from grocery stores, officials said. Results of additional tests are expected in "the next few days to weeks."

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The polymerase chain reaction (PCR) lab test the FDA used would have detected viral genetic material even after live virus was killed by pasteurization, or heat treatment, said Lee-Ann Jaykus, an emeritus food microbiologist and virologist at North Carolina State University

"There is no evidence to date that this is infectious virus, and the FDA is following up on that," Jaykus said.

Officials with the FDA and the USDA had previously said milk from affected cattle did not enter the commercial supply. Milk from sick animals is supposed to be diverted and destroyed. Federal regulations require milk that enters interstate commerce to be pasteurized.

Tests for viable virus underway, agency says

Because the detection of the bird flu virus known as Type A H5N1 in dairy cattle is new and the situation is evolving, no studies on the effects of pasteurization on the virus have been completed, FDA officials said. But past research shows that pasteurization is "very likely" to inactivate heat-sensitive viruses like H5N1, the agency added.

The agency said it has been evaluating milk from affectedanimals, in the processing system and on the shelves. It said itis completing a large, representative national sample tounderstand the extent of the findings.

The FDA said it is further assessing any positive findingsthrough egg inoculation tests, which it described as a goldstandard for determining viable virus.

Interstate cattle must be tested for bird flu

On Wednesday, the U.S. government said it willrequire dairy cattle moving between states to be tested for birdflu starting on Monday, Agriculture Secretary Tom Vilsack toldreporters.

The USDAsaid it found H5N1 in the lung of an asymptomatic dairy cow that was sent to slaughter without entering the food chain.

Vilsack said all laboratories and states in the countrymust report positive tests in cattle for any influenza A, andthe USDAwould pay forincreased testing.

Positive flu tests in cattle will prohibit animals frombeing moved during a 30-day waiting period and until they testnegative, Vilsack said.

The USDA said last week that cow-to-cow transmission was afactor in the spread of bird flu in dairy herds, but it stilldid not know exactly how the virus was being moved around.

Matt Herrick, a spokespersonfor the International Dairy Foods Association, said that time and temperature regulationsfor pasteurization ensure that the commercial U.S. milk supply is safe. Remnants of the virus "have zero impact on human health," he wrote in an email.

Scientists confirmed the H5N1 virus in dairy cows in March after weeks of reports that cows in Texas were suffering from a mysterious malady. The cows were lethargic and saw a dramatic reduction in milk production. Although the H5N1 virus is lethal to commercial poultry, most infected cattle seem to recover within two weeks, experts said.

To date, two people in the U.S. have been infected with bird flu. A Texas dairy worker who was in close contact with an infected cow recently developed a mild eye infection and has recovered. In 2022, a prison inmate in a work program caught it while killing infected birds at a Colorado poultry farm. His only symptom was fatigue, and he recovered.

The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute's Science and Educational Media Group. The AP is solely responsible for all content.