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?

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,

Three government agencies—the FDA, the CDC, and the U.S. Department of Agriculture—share responsibility for the bird-flu response, and it’s unclear which agency is truly in charge. The USDA, for example,

As of Monday evening, there is only one confirmed human case of bird flu in Missouri. The single case is one of 15 reported nationwide since 2022. However, the recent Missouri case is unusual... because there is no known animal link to that case.

Health authorities in the US are studying seven people who developed influenza symptoms after being exposed to a Missouri bird flu patient, raising the possibility of the first human-to-human transmission of the infection.

The United States is in the middle of an unprecedented bout of bird flu, also known as H5N1. Since 2022, the virus has killed millions of birds and spread to mammals, including co