A strain of avian influenza that has killed millions of birds in recent years has now been detected in dairy cows in several states, prompting concerns about the safety of the U.S. dairy supply.
Federal health and agriculture officials released a statement last week stressing that there “continues to be no concern” about the safety of the commercial milk supply, while underscoring that the agencies are continuing to monitor the situation as it evolves.
Scientists know that bird flu can spread to humans when they come into contact with infected animals, including dead ones, without wearing protective gear, which seems to have been the case with a person recently infected in Texas. So far, there isn’t any evidence to suggest that humans can contract bird flu by consuming food that has been pasteurized or cooked, said Benjamin Chapman, a professor and food safety specialist at North Carolina State University.
“That’s not to say it couldn’t happen,” he said. “It’s just that we have a pretty robust history of it not happening. And that’s good news.”
However, there are a few key points that researchers are still working to understand, Dr. Chapman and other experts said, like just how widespread the current outbreak is in cows, or exactly how the virus spread to them. Public safety agencies have said that it’s not clear what risks surround unpasteurized products.
“In the column of known versus unknown, there’s a lot more in the unknown part,” said Dr. Gail Hansen, a veterinary public health expert and independent public health consultant.
What do we know about bird flu and dairy products?
Avian flu was detected in unpasteurized milk samples from sick cows last month, but the Food and Drug Administration has said that the commercial supply of pasteurized milk remains safe and that it “does not currently have concerns” about pasteurized cheese. Milk from sick cows is being diverted or destroyed so it does not end up on store shelves.
The pasteurization process, which works by heating milk to destroy pathogens, will kill influenza, said Matthew Moore, an assistant professor in the department of food science at the University of Massachusetts, Amherst.
Raw or unpasteurized milk, which has become increasingly accessible in the United States over the last decade, already puts people at a higher risk from harmful germs. “Now there’s a whole new level of concern,” said Darin Detwiler, a food safety expert and professor at Northeastern University’s College of Professional Studies. “I don’t think that one can make an argument that we shouldn’t be concerned about drinking raw milk in this era.”
The F.D.A. said that it does not yet know whether people can contract avian flu by consuming raw milk and cheese products made from infected cows. The agency recommended that manufacturers refrain from making raw milk or raw milk cheese from cows that show symptoms.
What about meat?
The confirmed cases so far have been in dairy cows, not those used for meat, and the U.S. Department of Agriculture said it is “confident that the meat supply is safe.” The agriculture industry has safeguards to identify and quarantine sick animals so that they do not end up in the food or dairy supply. Scientists are still trying to figure out if cows shed the virus before they are symptomatic; if they do, it could raise new concerns.
But proper cooking would render the virus harmless, said Aljoša Trmčić, a dairy safety expert at the Cornell College of Agriculture and Life Sciences.
The same precautions that prevent people from getting sick from pathogens such as salmonella can help prevent contamination with the virus, Dr. Chapman said.
The U.S. Department of Agriculture recommends four simple steps: frequently clean your hands and the surfaces you use to prep food with soap and water; keep raw meat, poultry, fish and juices separate from other foods; use a food thermometer to ensure you’ve cooked food to the right temperature; and do not leave food at room temperature for more than two hours, or for more than one hour when the temperature is above 90 degrees.
“All the precautions that you would normally take for just sensible handling of raw meat would be good enough,” Dr. Moore said.
Are eggs safe to eat?
Cal-Maine Foods, a major producer of eggs in the United States, announced this week that it had detected avian flu in a Texas facility and culled over one million birds. Infected hens most likely will lay eggs that are also infected with the virus, Dr. Trmčić said, but he added that it’s very unlikely for a contaminated egg to make it onto the market with the industry controls in place.
Egg products — like liquid egg whites — are pasteurized. But most whole eggs sold in cartons are not pasteurized on the inside, Dr. Trmčić said. You need to properly cook them to kill pathogens like avian flu, but also more common germs like salmonella. That includes making sure both yolks and whites are firm, not runny. You may also want to avoid dough, sauces, drinks or other items that use raw or undercooked eggs, Dr. Detwiler said.
“I’m not saying avoid eating eggs or avoid drinking milk,” Dr. Detwiler said. “Go forward with caution, and think about how some practices may have more risk than others.”