CDC officials said the study suggests asymptomatic workers who engage in jobs that put them at high risk for exposure at poultry and dairy farms might be at heightened risk. The CDC had recommended testing be limited to workers who had symptoms after ...

Following a CDC study showing bird flu exposure among dairy workers, health officials recommend increased testing and preventative measures for farmworkers, even if they show no symptoms, to prevent virus spread and mutation.

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.

The H5 bird flu is widespread in wild birds and is causing outbreaks in U.S. poultry and dairy farms, the CDC says. There have been outbreaks in 443 U.S. dairy herds, and 48 states have reported outbreaks in poultry.

The health agency now urges proactive testing and treatment for the virus among any workers who were exposed to H5N1.