After a new study showed that bird flu has spread to dairy farm workers more often than previously known, the US Centers for Disease Control and Prevention is expanding its recommendations for testing and treatment of workers on farms where animals have tested positive.

About 7% of dairy workers exposed to the avian flu that is spreading through U.S. herds have become infected themselves, federal experts estimate. That number highlights concerns that circulating strains of bird flu might become highly infectious in humans,

The CDC said Thursday it is updating its recommendations for testing, treatment and protection for workers who may be exposed animals infected with bird flu.