The Washington State Department of Health (DOH) has confirmed that a resident of Grays Harbor County is the first person in the U.S. known to be infected with the H5N5 strain of avian influenza.
The case also marks the country's first human bird flu diagnosis since February.
The patient, described by officials as "an older adult with underlying health conditions," remains hospitalized after showing influenza-like symptoms in early November.
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The DOH stated that the individual "had a mixed backyard flock of domestic poultry at home that had exposure to wild birds.
"Additional testing shows the virus to be H5N5, an avian influenza virus that has previously been reported in animals but never before in humans."
Domestic poultry and wild birds are considered the most likely sources of the virus exposure, though the health investigation is ongoing.
Public health experts have not found any increased risk to the public to date, according to the press release.
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"Transmission of avian influenza between humans is extremely rare and has never been documented in the United States," the report states.
The Centers for Disease Control and Prevention and DOH "currently consider the risk to the public from avian influenza to be low."
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The DOH urges poultry owners, wildlife handlers and others who have contact with animals to exercise caution.
Measures include avoiding contact with sick or dead birds, using appropriate protective equipment and reporting sick wildlife or domestic animals to the Washington State Department of Agriculture (WSDA).
The release also emphasizes that although the seasonal flu vaccine does not prevent bird flu infections, it is important because "infection with both viruses could result in the emergence of an avian influenza virus that is more easily transmitted from person to person."
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Previously this year, the CDC declared the bird flu emergency officially over.
The agency's emergency response to H5N1 bird flu, which was activated in 2024, was "deactivated" July 2, the agency told Reuters, citing declining animal infections and an absence of human cases since February.
The H5N5 virus is a close cousin of H5N1. While both viruses come from birds and share part of their genetic code, H5N5 has a different "end piece" of its structure that changes how it behaves, experts say.
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While H5N1 has caused human illness - and even deaths - for years, H5N5 has mostly been limited to birds until now, per health officials.
