None of the health care workers or other contact have tested positive for avian flu antibodies so far — but could their illness signal human-to-human transmission?

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, U.S. health officials said on Friday.

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.

In what could be the first cases of bird flu spreading between humans in the United States, a group of potential H5N1 infections in Missouri has now grown to eight. However, state health officials are still awaiting antibody tests to confirm whether the H5N1 infection is growing,

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.

After a patient with bird flu was hospitalized last month, state and federal health officials first determined the patient may have infected one household member and two hospital workers. However, "Missouri has since identified four additional health care workers who later developed mild respiratory symptoms,

Four more health care workers are being treated for respiratory symptoms after being exposed to bird flu - bringing the total number of possible cases to seven. Emory's Dr. Neil Winawer discusses the significance of the recent findings with Alyse Eady.