In other developments, CDC and Ohio partners launched a serosurvey among bovine veterinary workers who attended a recent professional conference.

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.

A third close contact of a patient in Missouri who was hospitalized with H5N1 bird flu has reported that they also experienced symptoms, the US Centers for Disease Control and Prevention said Friday.

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.