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*Update* The FDA has continued dairy products and has reaffirmed the safety of pasteurized dairy. You can read the latest from the FDA as they update here.

The US Food and Drug Administration (FDA) has conducted initial tests on pasteurized milk purchased from grocery stores in areas where cows have tested positive for H5N1 influenza or bird flu. The tests indicate that the milk is not infectious and cannot make people sick. The FDA used the “gold-standard” egg inoculation tests to determine whether live virus was present in the milk samples. The test results are reassuring, as the virus did not grow in the fertilized eggs. The FDA also tested infant and toddler formula made with powdered milk, and no traces of the H5N1 virus were detected.

According to an announcement last Thursday, the FDA has found that around 1 in 5 milk samples taken from grocery stores have tested positive for gene fragments of the virus. The agency also stated that it had found more positive samples in areas where infected herds are present, but it didn’t reveal the locations where the milk samples had tested positive.

“These results reaffirm our assessment that the commercial milk supply is safe,” the FDA said in an update Friday.

The FDA has clarified that the presence of the H5N1 virus in milk does not necessarily mean that it is harmful to humans. In the United States, most milk is pasteurized, which involves heating it briefly to eliminate pathogens, including viruses like H5N1. However, the FDA is conducting more tests to ensure that the pasteurization process is effective in this case.

“To date, we have seen nothing that would change our assessment that the commercial milk supply is safe. Results from multiple studies will be made available in the next few days to weeks,” the agency said.

Not everyone is reassured, though.

Dr. Eric Topol, founder of the Scripps Research Translational Institute, said the finding of viral particles in milk on grocery store shelves means the outbreak is more widespread than we’ve known.

“The dissemination to cows is far greater than we have been led to believe. The FDA assurance that the dairy supply is safe is nice, but it’s not based on extensive assessment yet, which they acknowledge, and won’t engender trust and confidence because it comes in the wake of USDA mishandling,” he added.

In late March, highly pathogenic avian influenza was found in dairy cows in Texas and Kansas, marking the first time the virus had been detected in cattle. Infected cows have since been found in over 30 farms across nine states. Scientists have criticized the USDA for lacking transparency and being slow to share information.

Infected cows showed decreased appetite and discolored milk with the virus present in their mammary glands. Researchers are still investigating the source of infection and transmission between animals. Cats living on the same farms have died, possibly due to exposure to infected cow’s milk.

The FDA said Tuesday that milk from sick cows is being “diverted or destroyed” while milk sold in interstate commerce is being pasturized in order to eliminate pathogens… but pasteurization doesn’t make milk sterile, so the agency tests milk samples from grocery stores.

The FDA stated, “Even if the virus is detected in raw milk, pasteurization is generally expected to eliminate pathogens to a level that does not pose a risk to consumer health.”

It is worth noting that the FDA does not recommend drinking unpasteurized or raw milk due to the health risks from germs.

The USDA’s Animal and Plant Health Inspection Service maintains a list of diseases that must be reported in animals. Although bird flu or avian influenza must be reported in poultry and wild birds, it is not obligatory in cattle. In other words, all reports of sick cattle have been voluntary.

“No one ever thought it was going to be in cows,” said Dr. Richard Webby, director of the World Health Organization’s coordinating center for studies on the ecology of influenza at St. Jude’s Children’s Research Hospital.

“You wouldn’t even think of an H5N1 in cows being something you’d ever have to worry about, and I think that’s where it’s fallen through the cracks a little bit.”

Farmers are compensated for birds & eggs that are destroyed to contain outbreaks like this. That further incentivizes farmers to be forthcoming with information. No such policies are in place for other livestock.

One major concern is that the current outbreak could potentially spread to pigs, as farms that raise cows also typically keep other types of animals.

The flu viruses enter cells through sialic acids, which act as entry points. For now, the H5N1 virus has yet to learn to access the human version of the sialic acid receptor efficiently.

Pigs have the same sialic acid receptors as both birds and humans in their respiratory tracts. If H5N1 causes a large outbreak in pigs, it would give the virus a perfect opportunity to learn to attach to human sialic acids.

“Pigs are a more efficient mixing bowl,” said Dr. Peter Hotez, a professor of pediatrics, molecular virology, and microbiology at the Baylor College of Medicine in Houston. “The one thing about where we are in Texas is that, besides those cattle, Texas is the epicenter of the feral hog population.”

“In the United States, we have 30% of the nation’s feral hogs, 2 to 3 million feral hogs, and so that to me is a potential risk, as well,” he said.

The CDC is currently keeping an eye on emergency department data and flu testing data in areas where H5N1 viruses have been detected in dairy cattle. Their aim is to detect any unusual trends in flu-like illness, flu, or conjunctivitis. According to a statement compiled by CDC officials, these data remain within expected ranges, and so far, no unusual trends or activity have been observed through surveillance systems. Jason McDonald, a CDC spokesperson, stated that 23 people with exposures to H5N1 have been tested, including one person in Texas who previously tested positive. No other people have tested positive in the current outbreak.