Federal authorities detected no live avian influenza virus in initial milk tests

On Friday, federal regulators announced that no live avian influenza virus had yet been found in the first batch of retail milk samples tested. This is an encouraging sign that despite the virus outbreak among dairy cows, milk in stores remains safe.

in Online updatethe Food and Drug Administration said the first round of tests, which look for live virus rather than just genetic fragments, suggested that the pasteurization process effectively neutralized the pathogen.

“These results reaffirm our assessment that the commercial milk supply is safe,” the FDA wrote in an update, adding that testing efforts are ongoing.

Officials also tested infant and toddler formulas containing powdered dairy products, but no virus was detected, the agency wrote.

The FDA launched a nationwide survey of milk samples shortly after an outbreak of the avian influenza virus, called H5N1, was discovered among dairy cows. Government scientists are testing 297 samples of retail dairy products from 38 states, covering an area well beyond the nine states where herds are known to be infected.

The first type of test that regulators run is a type of polymerase chain reaction (PCR), which is relatively quick but only detects the genetic traces of the virus and does not indicate whether a live pathogen is present. Researchers don't know.

On Thursday, the FDA said these tests show that approximately 1 in 5 retail milk samples nationwide contain fragments of the avian influenza virus, making the avian influenza virus much more prevalent than previously known. The findings suggest that the disease is widespread among cattle.

The samples containing the gene fragments are then tested for live avian influenza viruses. If the virus is present, it can pose a wide range of health threats.

A live virus test called egg inoculation is the most sensitive of its kind, but it is time consuming. The process involves injecting some of the dairy product into chicken eggs, waiting for the virus to multiply inside the egg, and then looking for signs of infection.

Eggs are an efficient container for the influenza virus to grow. Even in scarce quantities, it will thrive there. The FDA's new results therefore strongly suggest that the samples tested do not contain infectious virus and that pasteurization is working, the scientists said.

The negative results reported Friday were from a “limited, geographically targeted sample,” FDA officials said, without disclosing the source of the samples.

“Right now the answer seems to be pretty conclusive that pasteurized milk is safe,” said Samuel Scarpino, a professor of health sciences at Northeastern University. “The fact that it came back negative is strong evidence that there is no live virus present, at least in the sample tested.”

Experts say raw milk is never safe to drink and poses additional risks amid an outbreak of avian influenza in cows. Almost all milk produced on U.S. farms is pasteurized, a process that uses heat to kill pathogens. Influenza viruses are known to be sensitive to heat.

Scientists stressed that the federal government needs to test more milk samples and continue testing as long as the outbreak continues. Some criticized authorities for not acting sooner.

“The FDA should have done these tests six weeks ago when we first heard about this,” Dr. Scarpino said, referring to the outbreak among cattle.

Dr. Scarpino also called on the government to conduct egg inoculation experiments using milk containing varying concentrations of viral genetic material. These tests could provide reassurance that even pasteurized milk, which contains large amounts of genetic fragments, is safe to drink, he said.

In addition to pasteurization, other existing safety procedures require milk from clearly symptomatic cows to be removed from the commercial supply. More research is needed, but Dr. Scarpino said, “Once you start adding these things up, it becomes very unlikely that there is actually a problem.”

Andrew Bowman, a veterinary epidemiologist at The Ohio State University, has studied 150 retail milk samples collected around the Midwest, and the FDA's findings add to the ongoing live virus testing he has been conducting. He said it reflects the results.

The FDA's analysis on Friday showed it remains unlikely that replicating virus could be detected anywhere in retail milk samples.

“I have a gallon of milk in the fridge, I might use it tonight,” he said.