First U.S. Human H5N5 Bird Flu Case Confirmed in Washington; Patient Hospitalized

Washington resident hospitalized with first known human H5N5 infection in the U.S.

The Washington State Department of Health confirmed that an older adult with underlying medical conditions has been hospitalized after testing positive for H5N5 avian influenza. Laboratory testing identifies this as the first documented human infection with H5N5 in the United States, officials said.

Public health investigators report the person keeps a mixed backyard flock that had contact with wild birds, making the household birds or wild birds the most likely source of exposure. State and federal teams are continuing their investigation and conducting additional testing; the Centers for Disease Control and Prevention is awaiting a specimen from Washington for further analysis.

What experts say

Researchers and public health authorities say H5N5 is not believed to present a greater threat to people than H5N1, the strain linked to about 70 reported U.S. human infections during 2024–2025. Most of those earlier cases were mild and involved workers on dairy and poultry farms.

"These viruses behave similarly," said Richard Webby, an influenza researcher at St. Jude Children’s Research Hospital. "My gut instinct is to consider it the same as H5N1 from a human health perspective."

Scientists note the main difference between H5N5 and H5N1 involves a viral protein that influences how new virus particles are released from infected cells and spread to neighboring cells. As Webby explained, it is akin to different brands of car tires: both perform the same job but may be tuned for specific conditions that are not yet fully understood. H5N5 may also have different preferences for the bird species it infects more readily.

Context and precautions

Avian influenza has been detected in many wild and domestic bird populations since January 2022 and was identified in dairy cows for the first time in March of last year. Avian influenza can infect some mammals (including pigs, cattle and cats), and people can become infected through close contact with infected animals—so farm and poultry workers remain at higher risk.

Public health guidance

• If you keep backyard poultry, minimize contact between your birds and wild birds, practice good biosecurity, and isolate sick birds.
• Farm and veterinary workers should use appropriate personal protective equipment (PPE) when handling sick animals and follow employer and public health guidance.
• If you develop flu-like symptoms after contact with birds or other potentially infected animals, seek medical advice and tell providers about the exposure.

Authorities will update the public as more information and test results become available.