In what could be the first cases of bird flu spreading between humans in the United States, a group of potential H5N1

"Even sporadic cases of human-to-human transmission indicate a big change in the virus and suggest it is exploring new directions in virus evolution that bring it closer to a pandemic virus," James Lawler, MD, MPH, of the University of Nebraska Medical Center's Global Center for Health Security, previously told MedPage Today.

Seven people in contact with a patient hospitalized with bird flu also developed symptoms, the C.D.C. reported. Some are undergoing further tests.

The CDC said an investigation into a human H5N1 bird flu infection in Missouri has found four additional health care workers who fell ill after caring for the patient.

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

Health officials are investigating whether a person in Missouri who was hospitalized with bird flu in early September might have infected a handful of others. Testing is ongoing among five health care workers and a household member exposed to the infected person who all came down with mild respiratory symptoms.

Four more Missouri healthcare workers are experiencing mild respiratory symptoms after coming in contact with a bird flu patient, health officials said Friday. A total of six healthcare workers have now developed symptoms after having contact with the patient,

Four more health-care workers who tended to a person hospitalized with H5N1 bird flu have revealed that they had respiratory symptoms after their exposures, according to the US Centers for Disease Control and Prevention.

By Julie Steenhuysen (Reuters) -Four additional healthcare workers in Missouri who came in contact with a hospitalized bird flu patient developed mild respiratory symptoms but the virus was not confirmed in any of them,

Four additional healthcare workers in Missouri who were in contact with a bird flu patient developed mild respiratory symptoms but the virus was not confirmed in any of them, U.S. health officials said.