The U.S. Department of Agriculture (USDA) said on Wednesday that all the ground beef samples sent to the National Veterinary Services Laboratories (NVSL) for PCR testing were negative for the H5N1 bird flu virus.

To date, the US Department of Agriculture has tallied 32 affected herds in eight states: Idaho, Kansas, Michigan, New Mexico, North Carolina, Ohio, South Dakota, and Texas. In some cases, the movement of cattle between herds can explain the spread of the virus.

Additional testing of retail dairy products from across the country has turned up no signs of live bird flu virus, strengthening the consensus that pasteurization is protecting consumers from the threat, federal health and agriculture officials said at a news briefing on Wednesday.

But the leap of the H5N1 influenza strain, widespread among wild fowl and a regular threat to domestic poultry, into cattle was unexpected, and a worrisome development, as the more the virus spreads, the more chances it has to mutate. The COVID-19 pandemic was a stark lesson in the risk of “spillover,” when pathogens spread from animals to humans.

U.S. sellers of raw milk appear undeterred by federal health warnings for consumers to avoid drinking unpasteurized milk in light of a bird flu outbreak that has affected dairy herds in nine states and sickened at least one dairy farm worker.

Particles of bird flu virus have come up in milk, sour cream and cheese samples. Baby formula has tested negative. See what products are safe.

The U.S. Food and Drug Administration said on Wednesday that preliminary results of additional testing of more dairy products has shown that pasteurization inactivates the bird flu virus. The FDA released results from tests of products including sour cream and cottage cheese,

Ongoing testing of milk and dairy products by the US Food and Drug Administration has not found any active H5N1 bird flu virus in 297 samples of products purchased in grocery stores, the agency said Wednesday.

Bird flu typically spreads among birds, but there have been recent outbreaks among cattle in the U.S., and one Texas man contracted the virus from sick cows. Here’s why so many experts are worried about a possible new pandemic.