The Washington State Department of Health confirmed the first human H5N5 avian influenza infection in an older adult hospitalized in early November. Investigators believe the virus was transmitted from backyard poultry exposed to wild waterfowl. Experts say human-to-human spread is unlikely now but stress ongoing surveillance, caution around sick animals, use of PPE when needed, reporting unusual animal deaths to the USDA, and getting the seasonal flu vaccine.
First Known Human Case of H5N5 Bird Flu Confirmed in Washington — What Experts Advise
The Washington State Department of Health confirmed the first human H5N5 avian influenza infection in an older adult hospitalized in early November. Investigators believe the virus was transmitted from backyard poultry exposed to wild waterfowl. Experts say human-to-human spread is unlikely now but stress ongoing surveillance, caution around sick animals, use of PPE when needed, reporting unusual animal deaths to the USDA, and getting the seasonal flu vaccine.
07:46 AM, 11/19/2025Health
Health officials in Washington state have confirmed the first known human infection with an H5N5 avian influenza virus. The patient, an older adult with underlying medical conditions, was hospitalized in early November and tested positive for the H5N5 subtype, according to the Washington State Department of Health.
Investigators believe the most likely source of infection was domesticated poultry in the patient’s backyard that had contact with wild waterfowl carrying avian influenza. Officials say this pathway — wild birds to backyard poultry to a human — is the most plausible explanation for how the virus reached the patient.
What experts say
Human-to-human transmission appears unlikely at this time. Public-health experts emphasize that avian influenza infections in people are typically linked to direct contact with infected birds or, in some cases, infected cattle or unpasteurized milk. “The risk to the general public is currently low outside those risk groups,” said Dr. Amesh Adalja, an infectious-disease expert and senior scholar at the Johns Hopkins Center for Health Security.
Researchers note that H5 viruses acquired mutations in 2021–2022 that made them more capable of infecting a wider range of mammals. Those changes helped migratory waterfowl spread the virus more broadly, contributing to outbreaks in poultry, wild animals and, more recently, on some dairy farms.
The Centers for Disease Control and Prevention (CDC) warns that infected animals can transmit avian influenza to people through saliva, mucus, feces and other bodily fluids, including milk. Sporadic human infections with avian strains — such as H5N1, H7N9, H9N2 and others — are recorded each year; there have been about 70 reported avian-flu cases in the United States since 2024.
Why this case matters
This is the first documented human infection with H5N5. Experts believe wild birds carrying H5N5 likely infected backyard poultry, which then transmitted the virus to the homeowner. “Now that the virus is more prevalent and recurs seasonally as migratory birds move, a human case linked to backyard poultry is not surprising,” said Benjamin Anderson, associate director at the University of Florida’s One Health Center of Excellence.
Although avian influenza can cause isolated human infections, it does not currently spread easily between people. For a bird flu virus to acquire efficient human-to-human transmission, it would typically need multiple mutations enabling it to bind human respiratory receptors. Another theoretical route is reassortment, where an animal infected with both a bird and a human influenza strain produces a new hybrid virus.
“Every bird flu strain has theoretical pandemic potential, but this particular strain appears less likely to spark a pandemic because only one human case has been detected so far,” said Dr. David Diemert, a professor of microbiology and immunology. The most probable outcome remains sporadic, isolated human cases tied to direct avian exposure.
Practical guidance
Public-health officials stress continued surveillance and testing. Key recommendations for people who keep backyard birds or work with poultry or dairy cattle include:
- Watch animals for signs of illness and avoid contact with sick or dead birds or cattle.
- Use appropriate personal protective equipment (PPE) when handling animals that might be infected.
- Report unusual sickness or unexplained deaths in birds or cattle to the U.S. Department of Agriculture.
- Seek testing and medical care if you develop symptoms after contact with potentially infected animals.
Experts also note that commercially produced poultry remains safe when properly cooked to an internal temperature of 165°F (74°C). Getting the seasonal influenza vaccine is recommended; even if it does not match an avian strain exactly, vaccination can reduce the risk of severe disease and help limit opportunities for influenza viruses to mix and evolve.
As of now, no additional human cases of H5N5 have been reported.