A Washington state resident has become the first person in the United States to test positive for a rare bird flu strain that has never before been found in humans.
The older adult, who has underlying health problems, was hospitalized in early November after developing a high fever, confusion and trouble breathing.
“This is a severely ill patient,” state epidemiologist Dr. Scott Lindquist told The Washington Post.
Experts stress that the public health risk remains low.
Testing by the Washington State Department of Health and the U.S. Centers for Disease Control and Prevention (CDC) showed the patient was infected with H5N5, a type of avian influenza seen in wild birds in the U.S. and Canada, but never before in a human.
Officials said the person cares for a mixed backyard flock and two birds had died weeks earlier. Wild birds also had access to the property, making poultry or wild birds the most likely source of exposure.
While H5N5 is different from the more common H5N1 strain that has spread widely among animals and people worldwide, experts say the two strains behave similarly.
"The H5N5 viruses we have looked at behave similarly to H5N1 viruses in our models to assess human risk," Richard Webby, a virologist at St. Jude Children’s Research Hospital, told The Post.
More than 100 health care workers who interacted with the patient have been monitored, and some were tested for flu-like symptoms.
"We have identified no additional individuals other than the patient who is infected with H5N5," state health officer Dr. Tao Kwan-Gett, said to The Post.
The CDC is working closely with Washington state and has been helping clinicians with treatment recommendations.
At this time, officials say there is no evidence of person-to-person spread.
Cases in U.S. poultry flocks began increasing in September, with 25 flocks infected in the first two weeks of November, already more than all of September, the CDC says.
Risk increases during the colder months because migratory birds can carry the virus and pass it to backyard flocks or commercial poultry, Seema Lakdawala, a virologist at Emory University, explained to The Post.
The CDC also remains alert for a potential early uptick in seasonal flu, which has already begun to rise in some countries.
Since 2024, 70 people in the U.S. have tested positive for bird flu, mostly workers exposed to infected dairy cattle or poultry.