The first U.S. human infection with the H5N5 avian influenza subtype has been reported in Washington state. The patient, described as an older adult with underlying conditions, was hospitalized with high fever, respiratory distress and confusion and remains under care. Investigators believe exposure came from backyard poultry linked to wild birds; no human‑to‑human transmission has been documented. The CDC is awaiting samples for further testing and says the risk to the public is low.
First U.S. Human H5N5 Bird-Flu Case Reported in Washington — CDC Investigating
The first U.S. human infection with the H5N5 avian influenza subtype has been reported in Washington state. The patient, described as an older adult with underlying conditions, was hospitalized with high fever, respiratory distress and confusion and remains under care. Investigators believe exposure came from backyard poultry linked to wild birds; no human‑to‑human transmission has been documented. The CDC is awaiting samples for further testing and says the risk to the public is low.
04:33 AM, 11/18/2025Health
Washington state health officials have confirmed the first U.S. human infection with the H5N5 avian influenza subtype.
A resident of Washington state has been diagnosed with a strain of bird flu not previously detected in people. This is the first human bird‑flu case reported in the United States since February. Officials described the patient as an older adult with underlying health conditions who was hospitalized after developing a high fever, respiratory distress and confusion; they remain in medical care.
Public health investigators believe the infection involves the H5N5 subtype. Earlier avian influenza infections reported this year were linked to the H5N1 subtype.
Scientists note the key biological difference between H5N5 and H5N1 lies in the neuraminidase protein — the “N” in the subtype name — which helps release newly formed virus particles from infected cells and can affect how the virus spreads between 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,” said Richard Webby, an influenza researcher at St. Jude Children’s Research Hospital.
Authorities emphasize there is currently no evidence that H5N5 poses a greater risk to people than other avian strains. To date, human‑to‑human transmission of avian influenza has not been documented.
Investigators suspect the patient likely acquired the virus through backyard poultry that had contact with wild birds. The Centers for Disease Control and Prevention is awaiting samples for additional laboratory testing and continues to assess the situation; the agency says the risk to the general public remains low.
Health officials advise that anyone with direct exposure to sick or dead poultry who develops fever, cough, shortness of breath or unusual illness should seek medical care and tell providers about their exposure. Public health teams are monitoring contacts and conducting follow‑up testing as needed.
Report contributions: The Associated Press.