First US Human Case of H5N5 Bird Flu Confirmed in Washington State — Patient Critically Ill; No Sign Yet of Human Spread

First US human infection with H5N5 confirmed in Washington State

A man in his late 60s from Washington State has been confirmed as the first person in the United States to contract H5N5 avian influenza. He was admitted to hospital in early November and remains in critical condition, local health officials said.

How this relates to other avian influenza strains

H5N5 is closely related to H5N1, the avian influenza strain that has infected more than 70 people in the US over the past year and has been responsible for the deaths of hundreds of millions of birds and other animals worldwide since 2020. Officials say there is currently no evidence that H5N5 transmits between people.

Likely source and ongoing investigation

Investigators have not yet established exactly how the Washington State man became infected. He kept a flock of domestic poultry at his home, which public health officials consider the most likely source of exposure. This is the first human avian-flu infection reported in the United States since February.

'Any time a new avian flu subtype is detected in a human, it’s notable,' said Krutika Kuppalli, associate professor in the division of infectious diseases at the University of Texas Southwestern.

Airfinity, a health intelligence firm that tracks outbreaks, said the case raises concerns that the virus 'may be acquiring features that enable human infection.' Authorities are monitoring virus samples and conducting contact tracing to detect any further spread.

Background and spread among animals

Wild birds are natural carriers of avian influenza and can spread the virus through droppings and saliva. As migrating wild birds move south for the winter, farmed chickens and turkeys increasingly encounter them, raising the risk of transmission into domestic flocks.

H5N5 was first identified in wild ducks in southern China in 2009 and has caused sporadic outbreaks among wild and domestic birds since. A newer H5N5 variant emerged in Russia in 2020 and has since been detected in North America and Europe. In 2023, H5N5 was detected in mammals for the first time — beginning with raccoons in Canada — and has since been found in other mammals, including a cat in Iceland and grey seals in Norfolk.

By contrast, H5N1 has recently jumped into cattle on US dairy farms and is responsible for most recent human infections tied to agricultural exposure. One US H5N1 case last year resulted in a fatality in Louisiana. Internationally, H5N1 has been linked to several deaths in Cambodia this year; public-health firms caution that sporadic urban spillovers remain possible as avian circulation evolves.

Expert view and public-health response

Experts say H5N5 currently appears less widespread among animals and less of an immediate threat to people than H5N1, but many uncertainties remain. 'Based on what we know right now, H5N5 does not appear to pose the same level of concern as H5N1,' said Dr Kuppalli. 'We need more data, but there’s currently no sign this virus spreads between people.'

Ed Hutchison, professor of molecular and cellular virology, noted that gaps in knowledge about which wild animals carry H5N5 and where it is circulating do not, by themselves, indicate an immediate human risk. Health authorities continue surveillance of poultry and wild-bird populations and are advising those who keep domestic birds to follow biosecurity guidance and report sudden illness or deaths in flocks.

What to watch for: updates from state and federal public-health agencies on testing results, contact tracing outcomes, and any evidence of human-to-human transmission. Owners of backyard and farm poultry should maintain good hygiene, limit contact between domestic and wild birds, and seek veterinary or public-health advice if animals become sick.