Missouri Case Update

Missouri continues to lead the investigation into that state´s only reported H5 case with technical assistance from CDC in Atlanta. As CDC learns new information from Missouri about its investigation, we are sharing it as quickly as possible in this space to help keep the public up to date. The Missouri Department of Health and Senior Services has not, to date, identified ongoing transmission among close contacts of the case, first reported on September 6, 2024. Missouri identified two health care workers who were exposed to the hospitalized case before droplet precautions were instituted (i.e., higher risk exposure) and subsequently developed mild respiratory symptoms (among 18 workers with this higher risk exposure); one tested negative for influenza by PCR, as previously reported, and the second provided a blood specimen for testing by CDC for potential influenza A(H5N1) antibodies. Missouri has since identified four additional health care workers who later developed mild respiratory symptoms. One of these workers was in the higher risk category and provided a blood specimen for H5 antibody testing. Three of these workers are among 94 workers who were exposed to the hospitalized case of avian influenza A(H5) after droplet precautions were instituted (i.e., lower risk exposure); blood specimens for those who became symptomatic have been collected for H5 antibody testing at CDC. Aside from the one health care worker reported to have tested negative for influenza by PCR, the five remaining exposed health care workers had only mild symptoms and were not tested by PCR for respiratory infections. PCR testing would have been unreliable at the time of discovery of these individuals´ prior symptoms. The health care worker monitoring effort has been part of the ongoing investigation as previously reported. Results of serology testing at CDC on the positive case and their previously identified household contact are still pending. To date, only one case of influenza A(H5N1) has been detected in Missouri. No contacts of that case have tested positive for influenza A(H5N1). CDC continues to closely monitor available data from influenza surveillance systems, particularly in affected states, and there has been no sign of unusual influenza activity in people, including in Missouri.