The outbreak has sickened 53 people in 16 states, including 31 who were hospitalized, according to the agency. The CDC said five victims have developed kidney failure.
A deadly form of bird flu has been confirmed in a southern Tennessee operation that supplies Tyson Foods with chickens, marking the first U.S. case at a commercial farm this year.
After the worst-ever U.S. outbreak of avian influenza destroyed almost 8 million turkeys earlier this year, there are fewer of them, and those that remain are smaller than normal.
Most of the 3.8 million egg-laying hens in an Iowa flock probably have bird flu as the biggest single outbreak of the virus reported in the U.S. added to concerns that turkey and egg supplies will be hampered by the disease.