The U.S. Centers for Disease Control and Prevention (CDC) reported September 6 that a person in Missouri had tested positive for avian influenza A (H5) (“H5 bird flu"). This is the 14th human case of H5 reported in the United States during 2024 and the first case of H5 without a known occupational exposure to sick or infected animals. H5 outbreaks in cattle have not been reported in Missouri, but outbreaks of H5 have been reported in commercial and backyard poultry flocks in 2024. H5N1 bird flu has been detected in wild birds in that state in the past. No ongoing transmission among close contacts or otherwise has been identified.

While other novel flu cases have been detected through the country's national flu surveillance system, this is the first time that system has detected a case of H5. In this case, the specimen from the patient originally tested positive for flu A, but negative for seasonal flu A virus subtypes. That finding triggered additional testing.

Without a known exposure to sick or infected animals, further sequencing may help determine if the virus is linked to the B3.13 genotype circulating in cows, if there are links to other human cases, or if there are ties to other animals, which could include birds or even cats, mice, or other wildlife.