A second Missouri healthcare worker who had contact with a hospitalized patient infected with bird flu developed mild respiratory symptoms but was not tested for the virus, U.S. officials said on Friday.

Three people in contact with a hospitalized bird flu patient in Missouri have developed symptoms, officials said.

A close contact of someone with bird flu became ill on the same day, the C.D.C. reported. But the second person was not tested, and the cause of the illness is unknown.

Another health care worker who was exposed to a Missouri patient who tested positive for bird flu developed respiratory symptoms but wasn't tested for the flu, U.S. health officials reported Friday. The news is rekindling worries of person-to-person transmission of the H5N1 bird flu strain.

Health officials identified three contacts, including two healthcare workers, who were closely monitored after a bird flu patient in Missouri was recently hospitalized.