The CDC's updated recommendations are based, in part, on the study of 115 dairy workers in Colorado and Michigan. Blood tests found eight workers had been infected with bird flu, but only four of those workers recalled having symptoms. The most common ...

The CDC study provides the largest window to date into how the bird virus first detected in March in dairy cows may be spreading to people. It suggests that the virus has infected more humans than the 46 farmworkers identified in the U.S. as of Thursday. Nearly all were in contact with infected dairy cows or infected poultry.