Blood testing of large-animal veterinarians suggests that H5N1 bird flu has spread more widely than US surveillance of the virus is capturing, according to a new study by federal and state disease detectives.

Out of 150 participating veterinary practitioners across the country, three had antibodies indicating recent infection with Type A H5N1 bird flu, based on blood samples collected in September 2024, noted Samantha Olson, MPH, of the CDC's National Center for Immunization and Respiratory Diseases, and colleagues.