The U.S. Department of Agriculture will test ground beef for bird flu particles, though officials said Tuesday they're confident the nation's meat supply is safe.

Bird flu has been found in nearly three-dozen dairy herds across nine states. The new testing is the latest effort by the USDA to track and understand how the virus is spreading among livestock.

Two studies will test if particles of the bird flu virus, called Type A H5N1, is found in beef for sale in the states where dairy cows have tested positive or in the muscles of dairy cows sent to slaughter. A third will test how cooking meat at different temperatures affects the virus using a bird flu surrogate.

A week ago, the U.S. Food and Drug Administration confirmed it found non-infectious remnants of the bird flu virus in pasteurized milk. The particles are inactive and pose no threat to consumers, experts said.

Scientists say there's no evidence to suggest people can get bird flu by consuming food that's been pasteurized or properly cooked.

The virus was first found in dairy cows this spring, and since then, H5N1 was detected in the lung tissue of a dairy cow culled and sent to slaughter.

So far, officials with the U.S. Centers for Disease Control and Prevention have not seen signs that the virus is changing to be more transmissible to people. Two farmworkers have been infected with bird flu since the outbreak began.

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AP Health Writer JoNel Aleccia contributed to this report.

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