### Investigation Reveals Mild Respiratory Illness in Missouri Health Workers Following H5N1 Exposure

An investigation into an unexplained human H5N1 infection in Missouri has identified four additional healthcare workers who developed mild respiratory symptoms after treating the infected patient in August, according to the Centers for Disease Control and Prevention (CDC). While it remains unclear if these workers were infected with H5N1, their illness following the care of the patient raises concerns about possible human-to-human transmission, a possibility that flu experts suggest warrants further investigation. Blood tests for antibodies may provide definitive answers.

The CDC has stated that they continue to monitor influenza data closely, especially in affected states like Missouri, but they have found no unusual influenza activity among the population. The CDC still considers the risk to the general public from the H5N1 outbreak to be "low."

Over the past 25 years, H5N1 bird flu has rarely been suspected to spread from person to person. However, no sustained transmission chains have been documented. This recent incident marks the third occasion Missouri has reported health workers with flu-like symptoms after treating the H5N1 patient, who was hospitalized from August 22 to August 25.

To date, seven individuals who were in contact with the confirmed case have experienced illness, including a household member and six healthcare workers. One healthcare worker tested negative for influenza while ill.

The ongoing identification of such cases weeks after the initial patient's hospitalization has raised concerns about the thoroughness of Missouri's investigation. The CDC can only intervene and provide investigators if the state requests help, which has not occurred. Michael Osterholm, director of the University of Minnesota's Center for Infectious Disease Research and Policy, emphasized the importance of public health credibility and expressed concerns over the delay in identifying potentially infected individuals.

Among the newly identified healthcare workers, one was exposed to the patient before preventive measures for respiratory pathogens were implemented, placing them at higher risk than the others. Blood samples from the five healthcare workers who became ill after caring for the patient are set to be sent to the CDC's headquarters in Atlanta, despite logistical delays caused by Hurricane Helene. Nearly 94 follow-up interviews with healthcare workers who had contact with the patient are nearing completion.

Previously, a household contact of the infected individual also fell ill on the same day as the patient, yet was not tested at the time. The CDC is presently examining a blood sample from this contact, looking for H5N1 antibodies.

The Missouri case is one of 14 H5N1 cases detected in the United States this year, amidst an H5N1 outbreak in dairy cattle identified in late March. As of the latest update, 239 herds across 14 states have tested positive for H5N1. However, Missouri has not reported any infected dairy herds.

Most farmers have been reluctant to test their livestock, and few states have mandated testing. Colorado and California have been exceptions; Colorado has conducted bulk tank testing on dairy farms, identifying 64 infected herds. California, which reported its first positive herd in late August, has confirmed 41 affected farms so far.

This report includes updates from the Missouri Department of Health and Senior Services.