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,

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.

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.

Signs of recent bird flu infection were found in three US veterinarians, two of whom had no known prior exposure, researchers said, suggesting potentially wider spread of the dangerous virus than has been suspected.