It also could mean there are more “virus–infected dairy cattle in states where infection in dairy cattle has not yet been identified,” the CDC says. Human cases of bird flu still remain rare, with only 68 cases confirmed in the United States by the CDC.

Three veterinarians had antibodies to bird flu virus, which suggests recent infection, the report said. None of them knew they were working with dairy cattle with known or suspect

The new study is more evidence that the official U.S. tally of confirmed human bird flu infections—68 in the past year—is likely a significant undercount.

The current human case count of H5N1 influenza in the US could be an underestimate, according to a new study from the Centers for Disease Control and Prevention (CDC). After testing 150 veterinarians,

New evidence suggests bird flu may have jumped from cattle to humans undetected, sparking concern among health experts.