Chances are low that human-to-human spread of bird flu occurred in a group of people who were exposed to a patient infected with the virus in Missouri, US health authorities said.

Missouri officials are under growing pressure from national public health experts to pinpoint the source of the state’s first human bird flu infection.

U.S. health officials have run into obstacles in their efforts to determine whether a Missouri person infected with H5N1 bird flu passed the virus on to others.

Presidents always seem to have a crisis to deal with. George W. Bush had 9/11. Barack Obama had the Great Recession. Donald Trump had the coronavirus pandemic. Joe Biden had the war in the Middle East. For America’s next president, the crisis might be bird flu.

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?

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 latest developments are highly concerning, as they raise the possibility that the H5N1 virus has evolved the ability to transmit from human-to-human and thus the potential to cause the next pandemic.

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,

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

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.