A person believed to be the first confirmed case of H5N5 avian influenza in humans has died, health authorities in US state of Washington said Friday.

The deceased was a Grays Harbor County resident, according to the Washington State Department of Health. 

What have health authorities said?

The department said it would not be releasing specific details relating to the deceased's name, gender or age out of respect for the family's privacy.

They did confirm that the person was an older adult with pre-existing health conditions.

"The risk to the public remains low. No other people involved have tested positive for avian influenza," state health authorities said.

"Public health officials will continue to monitor anyone who was in close contact with the patient for symptoms to ensure that human-to-human spread has not occurred," the department said and added: "There is no evidence of transmission of this virus between people."

According to the health department statement, the person had a backyard flock of domestic birds which they said was the likely source of infection.

What is H5N5 avian flu?

H5N5 is a sub-type of avian flu that is not believed to be a greater threat to human health than the H5N1 virus that has been behind a wave of 70 reported human infections in the US in 2024 and 2025.

Most of those have been mild illnesses in workers on dairy and poultry farms.

The distinction between H5N5 and H5N1 lies in a protein involved in releasing the virus from an infected cell and promoting spread to surrounding cells.

According to the Washington State Department of Health website the first human cases of H5 avian influenza were reported in Washington state in October 2024.

The department says that to date, there is no evidence of person-to-person transmission of avian influenza in Washington state.

Health authorities say birds and other animals infected with avian influenza shed the virus in their saliva, mucous and feces.

Edited by: Saim Dušan Inayatullah, Karl Sexton