A new report suggests that more Americans may be walking around with bird flu − and not even know it. Researchers from the Centers for Disease Control and Prevention randomly tested 150 veterinarians for H5N1, or bird flu, antibodies, which would indicate if they had a recent infection.

A new study shows the bird flu has silently spread from animals to some veterinarians. It echoes two smaller studies that detected evidence of infection in previously undiagnosed farmworkers.

Three veterinarians who work with cows have tested positive for prior infections of H5 bird flu, according to a study released today by the Centers for Disease Control and Prevention.