First U.S. Case of H5N5 Avian Influenza Confirmed in Washington State

A resident of Grays Harbor County, Washington has become the first person in the United States to be diagnosed with the H5N5 strain of avian influenza, according to the Washington State Department of Health (DOH). This case marks the first human bird flu diagnosis in the country since February.

The patient, described as “an older adult with underlying health conditions,” has been hospitalized since early November after developing influenza-like symptoms. Health officials identified exposure to infected birds as the likely source of infection.

“The individual had a mixed backyard flock of domestic poultry at home that had exposure to wild birds,” the DOH stated in its release. “Additional testing shows the virus to be H5N5, an avian influenza virus that has previously been reported in animals but never before in humans.”

While the investigation into the case continues, health authorities have not identified any increased risk to the general public. The Centers for Disease Control and Prevention (CDC) and Washington DOH currently assess the public health risk from avian influenza as low.

“Transmission of avian influenza between humans is extremely rare and has never been documented in the United States,” the health department emphasized in its statement.

This discovery comes just months after the CDC declared an end to the bird flu emergency related to the more widely known H5N1 strain. That emergency response, activated earlier in 2024, was deactivated on July 2 due to declining animal infections and the absence of human cases since February.

Health experts note that while H5N5 and H5N1 are closely related avian influenza viruses that share part of their genetic code, they have distinct differences. H5N5 has a different structural component that affects its behavior.

“H5N1 has caused human illness — and even deaths — for years, but H5N5 has mostly been limited to birds until now,” according to information provided by health officials.

The Washington DOH has issued precautionary guidance for individuals who have contact with birds or other animals. Poultry owners, wildlife handlers, and others in similar roles are advised to avoid contact with sick or dead birds, use appropriate protective equipment, and report sick wildlife or domestic animals to the Washington State Department of Agriculture.

Avian influenza viruses primarily circulate among wild bird populations, particularly waterfowl, and can spread to domestic poultry flocks. The current outbreak of highly pathogenic avian influenza has affected millions of birds across North America since 2022, with sporadic human cases occurring in individuals with direct animal exposure.

Public health officials are particularly concerned about the potential for co-infection with seasonal influenza and bird flu viruses. While the seasonal flu vaccine does not prevent avian influenza infections, vaccination is still important because “infection with both viruses could result in the emergence of an avian influenza virus that is more easily transmitted from person to person,” the health department warned.

This case represents a significant development in the evolution of avian influenza, as it marks the first documented human infection with the H5N5 strain. Health authorities continue to monitor the situation closely while emphasizing that the current risk to the general public remains low.

The CDC and state health agencies maintain surveillance systems to detect and respond to emerging infectious disease threats, including novel influenza strains that could potentially gain the ability to spread more efficiently between humans.