This year in the United States, 14 individuals have tested positive for avian influenza, commonly known as bird flu. Out of these, nine contracted the virus after being in contact with poultry, while four were exposed to dairy cows. The origin of the most recent case remains unidentified.
The Centers for Disease Control and Prevention (CDC) confirmed the latest case on September 6. Initially identified by the Missouri Department of Health and Senior Services, this case marks the first instance of someone contracting bird flu in the U.S. without known exposure to sick or infected animals. Health officials have yet to ascertain how the individual acquired the virus.
Nirav Shah, the CDC’s principal deputy director, stated in a news briefing that current evidence suggests this is an isolated case. However, he acknowledged that the case is concerning as it indicates the possibility of alternative transmission sources, potentially from another person or an unknown origin. Officials emphasize there is no proof of person-to-person transmission at this time. The CDC’s surveillance systems have not detected any unusual flu activity in the country, and the risk to the general public remains low.
“Our influenza surveillance system is designed to find needles in haystacks,” Shah explained during the briefing. “In this case, we found such a needle, but we don’t know how it got there.”
The Missouri case is notable for being the first to be identified through the nation’s flu surveillance system rather than targeted animal testing. This year, the H5N1 flu virus has led to significant poultry losses across the country and has also been detected in 200 dairy herds across 14 states, the latest being in California. The virus is increasingly appearing in other mammals, including foxes, mice, raccoons, and domestic cats, raising the potential for human infection with more animals harboring the virus.
It is unclear if the Missouri case resulted from this broader transmission, but health officials are investigating this possibility. David Boyd, a virologist at UC Santa Cruz, noted, “Regardless of the source, it’s concerning, because it suggests that there’s a lot of the virus out there. This indicates that there is widespread transmission among animal sources.”
On August 22, an adult patient in Missouri was hospitalized for underlying medical conditions and incidentally tested positive for influenza. The sample was sent to the Missouri State Public Health Laboratory, which determined it was not consistent with currently circulating seasonal flu strains.
This discrepancy prompted further testing by the CDC, which recently confirmed the presence of a bird flu strain, identified as H5. The CDC is conducting additional tests to determine the specific virus subtype, the “N” component of H5N1. Due to a very low concentration of viral genetic material in the patient’s specimen, a full genome sequencing, including the N part, has not yet been possible. Nonetheless, preliminary data suggests that the specimen is closely related to the H5 virus found in dairy cows.
