Bird flu infections were detected among cattle veterinarians tested last fall, including two people with no known exposure to animals with the virus, according to a report released by the U.S. Centers for Disease Control and Prevention on Thursday.

Three dairy veterinarians, including one who worked only in states with no known bird flu outbreaks in cows, had recent, undetected bird flu infections, according to a new study from the Centers for Disease Control and Prevention. The results are based on antibody testing of 150 veterinarians working in 46 U.S. states.

Three U.S. dairy veterinarians unknowingly had H5N1 infections, otherwise known as bird flu. This included one person who worked only in states without known outbreaks in cows, according to a new study from the U.