CDC Newsroom – July 14, 2024 – Four human cases of highly pathogenic avian influenza (HPAI) A(H5) (“H5 bird flu”) virus infection in the state of Colorado have been confirmed by the Centers for Disease Control and Prevention (CDC). This includes all three presumptive-positive cases reported by that state on Friday, July 12 and a fourth specimen that was later found to be presumptive-positive by the state on Friday. CDC also is aware of an additional (fifth) presumptive-positive case in Colorado that will be confirmed at CDC once the specimen arrives. All cases were in farm workers who were involved in the depopulation of poultry at a poultry facility experiencing an outbreak of HPAI H5N1 virus. A CDC team is on the ground in Colorado, supporting their assessment of the poultry outbreak and associated human cases. Given current information, CDC believes that the risk to the public from this outbreak remains low.

These are the first cases of H5 virus infection in poultry workers (as opposed to dairy workers) since 2022. The first ever U.S. case of H5 in a poultry worker was reported in Colorado during April 2022. On July 3, 2024, Colorado also reported a case of H5 in a dairy worker on an affected farm, so that state is experiencing ongoing H5N1 outbreaks on dairy and poultry farms.

The designation of the influenza virus neuraminidase (the N in the subtype) is pending influenza genetic sequencing at CDC. Attempts to sequence the virus in the clinical specimens are underway and will be made available within 1-2 days if successful. Additional analysis will look for any genetic changes to the virus that could alter the agency’s risk assessment.

CDC’s recommendations related to H5 have not changed at this time. An assessment of these cases will help inform whether this situation warrants a change to the human health risk assessment.

If the CDC recommendations change, there will be a clear and present need for devices that can test for this virus at scale.