Washington state health officials on Friday confirmed that a resident has been infected with H5N5 bird flu, marking the first known human case of that variant and the first reported human bird flu infection in the United States since February.
The patient, an older adult with underlying health conditions, remains hospitalized, state officials said. State health officials had announced a preliminary bird flu diagnosis on Thursday and confirmed the H5N5 identification on Friday.
State and federal health officials said H5N5 is not believed to pose a greater threat to human health than the H5N1 variant behind a recent stretch of U.S. infections. The distinction between the two strains is notable for surveillance purposes: H5N5 had not previously been documented infecting a human, making the case the first of its kind.
The H5N1 variant caused 70 reported human infections in the United States across 2024 and 2025, according to federal health data. Most of those cases were mild illnesses among workers on dairy and poultry farms, though the case count prompted expanded surveillance of avian influenza transmission from animals to people.
Bird flu viruses periodically jump from animal populations to humans, most commonly among people with direct contact with infected poultry or cattle. The Centers for Disease Control and Prevention has tracked H5N1 detections in wild birds, commercial and backyard poultry flocks, and dairy cattle herds across the country.
The identification of a new variant in a human host is expected to prompt further study of H5N5 and its characteristics, though officials said early indications do not suggest the strain spreads more easily between people than H5N1.