uly 12, 2024 – The state of Colorado has announced that three people have tested presumptive positive for highly pathogenic avian influenza (HPAI) A(H5) (“H5 bird flu”) virus infection. Specimens have been sent to CDC for confirmatory testing. All of the people who tested presumptive positive experienced mild symptoms and were workers who were involved in the depopulation of poultry at a poultry facility experiencing an outbreak of the H5N1 virus that is circulating in wild birds and has been causing multistate outbreaks in dairy cows and poultry. At the state’s request, CDC is sending a team to Colorado to support their investigation, which is ongoing.

CDC’s current risk assessment for the general public remains low. As we learn more, we will continue to assess the situation and provide updates. These preliminary results again underscore the risk of exposure to infected animals. There are no signs of unexpected increases in flu activity otherwise in Colorado, or in other states affected by H5 bird flu outbreaks in cows and poultry.

Human infections with this novel influenza virus (and others) are concerning because of the potential to cause severe disease. The other reason these types of human infections are concerning is because of their pandemic potential. If these viruses were to change to spread easily from person-to-person, it could trigger a pandemic, though, to date, we have not seen genetic changes in the virus that would make it more likely to transmit between humans.

CDC’s recommendations related to H5 have not changed at this time. Findings from the investigation will inform whether guidance changes are needed. The investigation will include looking into compliance with the recommended use of personal protective equipment. Historically, most human cases of bird flu infection have happened in people who are not wearing recommended personal protective equipment. An analysis of the virus sequences from this outbreak also will be important to determine if a change in the risk assessment is warranted.