A new Centers for Disease Control and Prevention study suggests that bird flu may be spreading under the radar in the U.S. In September, the CDC tested 150 veterinarians who primarily worked with cattle in the past three months.

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.

A new study shows that bird flu has silently spread from animals to some veterinarians. The study published Thursday by the Centers for Disease Control and Prevention echoes two smaller ones that detected evidence of infection in previously undiagnosed farmworkers.