A Washington state resident believed to be the first person to be infected with a rare strain of bird flu has died, state health officials announced.

The person — an older adult with underlying health conditions — was undergoing treatment for H5N5 avian influenza, according to the Washington State Department of Health. The person, who had been hospitalized in King County since early November, died on Nov. 21, health officials said.

The patient was from Grays Harbor County, over 100 miles southwest of Seattle, and had a backyard flock of "mixed" domestic poultry that were exposed to wild birds, according to health officials. State testing identified avian influenza virus in the backyard flock's environment, "making exposure to the domestic poultry, their environment, or wild birds the most likely source of exposure for this patient," health officials said.

Other people who were exposed to the backyard flock, environment, and the patient were being monitored for symptoms, according to health officials. The person's identity was not released out of respect for the family’s privacy.

Testing at the University of Washington Virology Lab identified the virus as H5N5, a variant of the influenza A virus, and the Centers for Disease Control and Prevention confirmed the result. Health officials said the patient is the first person in the world to be infected with the H5N5 strain of bird flu.

The H5N5 strain has previously been reported in animals, but it has never been reported in humans before. Health officials reiterated that the risk to the general public from the virus remains low.

"No other people involved have tested positive for avian influenza," the Washington State Department of Health said in a news release on Nov. 21. "There is no evidence of transmission of this virus between people."

Where does bird flu come from?

Avian influenza, more commonly known as bird flu, is a disease caused by influenza type A viruses that naturally occur in wild aquatic birds, according to the Washington State Department of Health. These viruses can spread to other bird species and sometimes mammals.

The viruses can be deadly to domestic birds, such as chickens and turkeys, but rarely infect humans, health officials said. Most human cases have occurred in people exposed to sick or infected animals. Human cases range from mild to severe.

Symptoms are similar to those of common flu, including fever, chills, body aches, sore throat, eye irritation, and fatigue, according to the CDC.

"The risk of avian influenza increases in the fall and winter because migratory birds can carry the virus and spread it to domestic animals, including commercial poultry farms and backyard flocks," according to the Washington State Department of Health. "Transmission of avian influenza between humans is extremely rare and has never been documented in the United States."

As of Nov. 23, 71 cases of bird flu have been reported in humans, according to the CDC. The majority of cases are tied to the H5N1 strain.

Of those cases, 41 were linked to infected dairy cows and 24 were connected to infected poultry, CDC data shows. California has seen the most cases with 38.

Who is at risk?

Bird flu most commonly spreads among wild birds but can also infect poultry, livestock, and other mammals, including goats, coyotes, and opossums. Dairy industry experts have said infection can lower a herd’s milk production by about a fifth.

Among those most at risk of infection are farmers, animal care providers such as veterinarians, and other workers exposed to infected animals or animal products.

The H5N1 strain has been spreading among commercial flocks of birds in the United States since February 2022, according to the Animal and Plant Health Inspection Service. H5 bird flu is easily transferable to backyard flocks or those used for mass food production.

An outbreak among chickens earlier in 2025 prompted a widespread egg shortage.

Raw or undercooked foods, including cheeses, can also carry the virus. The deaths of at least three house cats in 2024 were linked to raw foods contaminated with bird flu.

What can you do to protect yourself from bird flu?

The Washington State Department of Health has urged people with backyard poultry to avoid contact with sick or dead birds. Officials have advised people to report any illnesses in poultry to their state agriculture and health departments.

Health officials also recommend that people avoid contact with sick or dead wildlife and report ill or dead animals to wildlife agencies. "Never handle or allow pets near dead birds or other wildlife," the Washington State Department of Health said.

Eggs and chicken meat are considered safe to eat, as the U.S. Department of Agriculture regularly checks farms for bird flu, and chickens are put to death if the virus is detected on a farm. Beef is also considered safe if cooked to proper temperatures, and the commercial milk supply is tested regularly to confirm its safety, the USDA said.

Federal health officials recommend avoiding eating raw or undercooked food products, such as raw milk, which has been shown in some cases to contain the virus.

"It is especially important that people who may have exposure to domestic or wild birds get a seasonal flu vaccine," according to the Washington State Department of Health. "While the seasonal flu vaccine will not prevent bird flu infection, it reduces the risk of becoming sick with both human and avian influenza viruses at the same time."

Contributing: Michael Loria, Karen Weintraub, and Mary Walrath-Holdridge, USA TODAY

This article originally appeared on USA TODAY: Washington state resident dies after rare bird flu strain infection

Reporting by Thao Nguyen, USA TODAY / USA TODAY

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