Washington state health officials confirmed Friday that a resident has contracted a rare strain of bird flu, marking the nation’s first human case of avian influenza since February.

According to The Associated Press, the older adult, who has underlying health conditions, remains hospitalized. Preliminary testing announced Thursday identified the infection, and follow-up testing confirmed the diagnosis on Friday.

State and federal authorities said the virus is H5N5, a strain not previously seen in humans. “This appears to be the first known human infection with the H5N5 bird flu virus,” officials said.

Experts emphasized that the new strain does not appear to pose a greater threat to human health than H5N1, the virus responsible for about 70 reported U.S. human infections in 2024 and 2025. Most of those cases were mild and occurred in workers on dairy and poultry farms.

“These viruses behave similarly,” said Richard Webby, a flu researcher at St. Jude Children’s Research Hospital in Memphis, Tennessee. “My gut instinct is to consider it the same as H5N1 from a human health perspective.”

The Centers for Disease Control and Prevention issued a statement mirroring that assessment, noting that “no information would suggest the risk to public health has increased as a result of this case.” The agency is awaiting a specimen from Washington for additional testing.

The difference between H5N5 and H5N1 lies in a protein that helps the virus leave an infected cell and spread to nearby cells. “Think along the lines of different brands of car tires. They both do the same job, it’s just each is better tuned for specific conditions, which we don’t fully understand,” Webby explained.

H5N5 may also have a different preference for which birds it infects most readily. The patient, a resident of Grays Harbor County, has a backyard flock of domestic poultry that had been exposed to wild birds. Health officials believe either the domestic birds or wild birds were likely the source of the infection, though the investigation is ongoing.

Authorities continue to monitor the situation closely, but early indications suggest the virus is unlikely to spark a broader public health threat.