On Apr. 28, 2022, Centers for Disease Control and Prevention (CDC) reported that a person had tested positive for avian influenza A(H5) virus (H5 bird flu) in the U.S., as reported by Colorado and confirmed by the CDC.

The patient reported fatigue for a few days as their only symptom and has since recovered. The patient is being isolated and treated with the influenza antiviral drug oseltamivir. While it is possible the detection of H5 bird flu in this specimen is a result of surface contamination of the nasal membrane, that can’t be determined at this point and the positive test result meets the criteria for an H5 case. The appropriate public health response at this time is to assume this is an infection and take actions to contain and treat.

This case does not change the human risk assessment for the general public, which CDC considers to be low. However, people who have job-related or recreational exposures to infected birds are at higher risk of infection should take appropriate precautions outlined in CDC guidance.

CDC has been monitoring for illness among people exposed to H5N1 virus-infected birds since these outbreaks were detected in U.S. wild birds and poultry in late 2021 and into 2022. To date, H5N1 viruses have been found in U.S. commercial and backyard birds in 29 states and in wild birds in 34 states. CDC has tracked the health of more than 2,500 people with exposures to H5N1 virus-infected birds and this is the only case that has been found to date. Other people involved in the culling operation in Colorado have tested negative for H5 virus infection, but they are being retested out of an abundance of caution.

This is the second human case associated with this specific group of H5 viruses that are currently predominant, and the first case in the United States. The first case internationally occurred in December 2021 in the United Kingdom in a person who did not have any symptoms and who raised birds that became infected with H5N1 virus. More than 880 human infections with earlier H5N1 viruses have been reported since 2003 worldwide, however, the predominant H5N1 viruses now circulating among birds globally are different from earlier H5N1 viruses.