A routine flu screening in late summer found the H5N1 virus in a Missouri patient. Unlike the other reported cases of avian flu, this person did not report being in recent contact with animals.

Hospital workers reported respiratory symptoms after encountering a Missouri patient with H5N1 who had not been exposed to farm animals. Officials say bird flu transmission is unlikely.

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.

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.

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

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.

At least one household member and six healthcare workers who encountered the index case-patient are being investigated after showing symptoms of viral infection.

A second health worker who cared for a person hospitalized in Missouri with H5N1 bird flu developed mild respiratory symptoms but was not tested for influenza, the CDC reported.

A routine flu screening in late summer found the H5N1 virus in a Missouri patient. Unlike the other reported cases, this person did not report being in recent contact with animals.