Bird Flu Has Infected a Third U.S. Farmworker

A third farmworker in the United States has been found to be infected with bird flu, heightening concerns about an outbreak among dairy cattle first identified in March.

The worker is the first in this outbreak to have respiratory symptoms, including a cough, sore throat and watery eyes, which generally increase the likelihood of transmission to other people, federal officials said on Thursday.

The other two people had only severe eye infections, possibly because of exposure to contaminated milk.

All three individuals had direct exposure to dairy cows, and so far none has spread the virus to other people, Dr. Nirav Shah, principal deputy director of the Centers for Disease Control and Prevention, said at a news briefing.

That suggests that the virus, called H5N1, has not acquired the ability to spread among people and that the threat to the general public remains low, Dr. Shah said.

“This newest case does not change the C.D.C.’s H5N1 influenza risk assessment level for the general public,” he added. “We should remain alert, not be alarmed.”