A Washington State resident from Grays Harbor County has died after being infected with the H5N5 avian influenza virus, marking the first confirmed human case of the strain globally, health officials said on Friday.

The individual, described by the state’s health department as an older adult with underlying medical conditions, had maintained a mixed backyard flock of domestic birds.

Investigators identified H5N5 virus in the environment of the flock, pointing to domestic poultry or wild birds as the likely source of exposure.

State and federal health agencies emphasised that the risk to the general public remains low.

No additional human cases have been detected among those exposed thus far and there is no evidence of human-to-human spread of the virus.

Health officials said they are monitoring all close contacts of the deceased and individuals exposed to the bird environment for symptoms of infection.

The diagnosis follows preliminary confirmation earlier this month that the patient had influenza A subtype H5, which was subsequently characterised as H5N5—a strain previously seen in animals but not in humans.

The patient had been hospitalised after developing high fever, confusion and respiratory distress in early November.

Two backyard birds reportedly died of illness in recent weeks, and samples from the flock confirmed avian influenza presence.

Avian influenza strains occasionally infect humans, but have rarely done so in the United States.

The more common human-infecting strain to date has been H5N1, which has caused limited human infections and one prior U.S. fatality.

The emergence of H5N5 in a human is a significant epidemiological event, though experts say it does not necessarily indicate greater threat than existing strains.

The Washington State Department of Health notified healthcare providers with updated guidance on exposure screening, testing and infection control for influenza patients with bird-contact history.

Agriculture and wildlife authorities are cooperating to trace the source of the virus in the backyard flock and assess wild-bird exposure.

The state noted that migratory birds and domestic poultry can carry avian viruses and that transmission to humans remains extremely rare.

Officials reiterated that the greatest risk to the public remains seasonal influenza, and advised vaccination.

As surveillance continues, they stressed early detection, thorough contact monitoring and bio-security in backyard poultry remain the best tools to manage this novel human case.