More unidentified illnesses linked to unexplained bird flu case in Missouri

Enlarge / A warning sign outside a laboratory testing the H5N1 bird flu virus at The Pirbright Institute in Woking, UK, on Monday, March 13, 2023. (credit: Getty | Jason Alden)

More than a month after a person in Missouri mysteriously fell ill with H5-type bird flu, investigators in the state are still identifying people who became ill after contact with the patient, raising questions about the diligence of the ongoing health investigation.

On September 6, Missouri’s health department reported the state’s first human case of H5-type bird flu, one that appears closely related to the H5N1 bird flu currently causing a nationwide outbreak among dairy cows. But the infected person had no known contact with infected animals—unlike all of the other 13 human cases identified amid the dairy outbreak this year. Those previous cases have all occurred in dairy- or poultry-farm workers. In fact, Missouri has not reported bird flu in its dairy herds nor recent poultry outbreaks.

Given the unexplained source of infection, health investigators in the state have been working to track the virus both backward in time—to try to identify the source—and forward—to identify any potential onward spread. The bird flu patient was initially hospitalized on August 22 but recovered and had been released by the time the state publicly reported the case.