Additional testing of retail dairy products from across the country showed no signs of live avian influenza virus, strengthening the consensus that pasteurization protects consumers from the threat, federal health and safety officials said Wednesday. agriculture at a press conference.
But the extent of the avian flu outbreak in cattle remains unclear, as dairy herds are not routinely tested for the infection, scientists and other experts have noted.
Only one human infection, a mild one, has been reported on a Texas dairy farm that had direct contact with sick cows. But scientists fear there could be many more undetected infections, particularly among agricultural workers.
Just two dozen people have been tested for bird flu, federal officials said at the briefing. There have been no unusual increases in flu cases across the country, even in areas with infected cows, they added.
But Dr. Keith Poulsen, director of the Wisconsin Veterinary Diagnostic Laboratory, said farms are not required to test employees, many of whom are migrant workers reluctant to work with state health officials.
“How much are we ignoring because of anxiety and fear of what happens if you don't get an answer you like?” Dr. Poulsen said.
Until last week, potentially contaminated dairy products appeared to be the most immediate threat to the public. Federal regulators last week announced initial test results on about 95 retail milk samples: About one in five contained genetic fragments of the virus, which health officials say poses no threat to consumers.
More advanced testing later in the week detected no live virus in the samples, a relief for federal regulators.
On Wednesday, Dr. Donald A. Prater, acting director of the Center for Food Safety and Applied Nutrition at the Food and Drug Administration, said federal scientists examined 201 additional samples of commercial dairy products, including milk, cottage cheese and sour cream.
So far, scientists have found no evidence of potentially infectious viruses. “The findings from U.S. government partners, as well as academic researchers, do not change our assessment of the safety of milk,” Dr. Prater said.
Dr. Prater said the FDA strongly advises against consuming raw, unpasteurized dairy products. Federal scientists are still examining the data to see if the virus in raw milk could be contagious, he added.
As of Wednesday, the outbreak had spread to 36 farms in nine states, according to the Department of Agriculture. Scientists have criticized the Biden administration for not conducting more animal testing to determine the scope of the outbreak.
Some dairy farms have been difficult to access, and owners are sometimes reluctant to allow public employees entry to production facilities, federal officials said.
“There are a lot of farms out there that don't report data,” said Dr. Poulsen, the Wisconsin expert. “They don't report because they're really afraid of what might happen if they weren't negative.”
The Department of Agriculture has determined that lactating cows must test negative for influenza A virus, a class that includes avian influenza, before being transported across state lines. The rule also requires owners of herds with positive tests to provide data on the whereabouts of the cattle to help investigators track the disease.
But further guidance released last week revealed that farmers need to test only 30 cows in a group, potentially allowing infected cows in larger herds to move interstate undetected.
Dr. Rosemary Sifford, a senior USDA official, defended the size of the order, saying that 30 cows was a “statistically significant number to be able to determine the status of the batch.” The department now requires state labs and veterinarians to report any positive tests on cattle to the agency.
The USDA has also turned its attention to meat. Last week, Colombia became the first country to ban beef and beef products from some US states due to the bird flu outbreak.
Dr. José Emilio Esteban, a top USDA food safety official, said during the briefing that beef is safe to eat, but that the agency was conducting three studies to “improve our scientific knowledge to make sure we have further data.”
The department is testing ground beef from grocery stores, as well as the remains of slaughtered animals, in states known to have infected dairy cattle, Dr. Esteban said. The agency is also examining the effectiveness of cooking in killing the virus by heating beef patties to three different temperatures.
Preliminary testing showed no evidence of the virus in ground beef, the USDA said Wednesday evening.
Officials are also looking at possible ways to compensate dairy farmers for “their cooperation and adoption of additional biosecurity practices,” Dr. Sifford said.
Underlying much of the concern about the livestock outbreak is the fear among scientists that the avian influenza virus is adapting to mammals. Dr. Sifford said during the briefing that federal scientists have not detected any changes in the virus that allow it to spread more easily among humans.
Dr. Demeter Daskalakis, a senior official at the Centers for Disease Control and Prevention, acknowledged that only about 25 people have been tested for the infection, about the same number reported last week.
Over 100 people are being monitored for symptoms. Dr Daskalakis said the number of people tested and monitored was “dynamic”, partly because the monitoring period for people with symptoms ends when they recover.
Emily Anthes contributed reporting.