The Centers for Disease Control and Prevention should have results later this month that provide more insight into how a Missouri resident, who hadn’t had any contact with infected animals or food, contracted a case of highly pathogenic avian influenza.

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.

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

Missouri State Epidemiologist George Turabelidze, facing mounting pressure from health experts to be more transparent while investigating the state's first bird flu case, recently gave an exclusive interview with the Washington Post.

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.

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.

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.

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

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?

A second Missouri healthcare worker who had contact with a hospitalized patient infected with bird flu developed mild respiratory symptoms but was not tested for the virus, U.S. officials said on Friday.