First Human Fatality from Rare H5N5 Bird Flu Strain Reported in Washington State

A Washington State man has tragically become the first known human fatality globally from the H5N5 strain of avian influenza, health officials confirmed on Friday, November 21, 2025. The older adult, who had underlying health conditions, was hospitalized earlier this month after exposure to his backyard poultry flock, according to the Washington State Department of Health.

The man, a resident of Grays Harbor County, was receiving treatment in King County, where Seattle is located, for symptoms including high fever, confusion, and respiratory distress, as reported by the Los Angeles Times. This case marks a significant, albeit rare, development in the global monitoring of avian influenza viruses.

Health officials have emphasized that the risk to the general public remains low, with no evidence of human-to-human transmission detected in this case or any other avian influenza incidents in the U.S. The Centers for Disease Control and Prevention (CDC) and the Washington State Department of Health continue to assess the situation.

The infection source was traced to the man's mixed backyard poultry flock, which had contact with wild birds, according to the Washington State Department of Health. Investigations confirmed the presence of the avian influenza virus in the flock's environment, making it the most probable origin of the patient's exposure.

While H5N5 had previously been identified in animals, particularly in wild birds across the U.S. and Canada, this is the first documented instance of the strain infecting and proving fatal to a human, as noted by The Guardian. Public health authorities are closely monitoring individuals who had close contact with the patient.

This incident follows a previous U.S. fatality from the H5N1 strain of bird flu in January 2025, involving a Louisiana man with backyard poultry, The Washington Post reported. Despite the severity of this new case, experts suggest H5N5 is not considered a greater threat to human health than the more common H5N1 strain.

The Washington State Department of Health, in collaboration with local health departments and the Washington State Department of Agriculture, is conducting ongoing investigations into the exposure and animal health aspects of this case. They reiterate that transmission between humans is extremely rare and has never been documented in the United States.

• Background of Avian Influenza Strains: Avian influenza, or bird flu, is caused by influenza A viruses naturally occurring in wild aquatic birds, which can then infect other bird species and occasionally mammals, according to the CDC. While many strains exist, H5N1 has been widespread globally in wild birds, poultry, and dairy cows, leading to approximately 70 human infections in the U.S. during 2024 and 2025, mostly presenting as mild illnesses in farm workers, as detailed by The Washington Post and CDC.

• Rarity of H5N5 in Humans: The H5N5 strain, while present in animal populations since at least 2023 when it infected birds and mammals in eastern Canada, had never before been detected in a human prior to this Washington State case, the Los Angeles Times reported. The BMJ noted that H5N5, like H5N1, generally causes mild illness in humans, but both are capable of causing severe disease, especially in higher-risk individuals.

• Symptoms and Severity: The Washington State patient experienced severe symptoms including a high fever, confusion, and respiratory problems, as reported by kesq. The CDC indicates that while most human cases of bird flu have been mild, severe cases can lead to complications such as pneumonia, respiratory failure, acute respiratory distress syndrome, and multi-organ failure, according to The Economic Times.

• Public Health Response and Monitoring: Following the diagnosis, public health officials initiated monitoring of over 100 healthcare workers and other close contacts of the patient for any signs of illness, as confirmed by The Washington Post. The Washington State Department of Health confirmed that no other individuals have tested positive for avian influenza, reinforcing the assessment that the risk of human-to-human transmission remains low.

• Expert Reassurance on Transmission: Virologists have largely downplayed the risk of widespread human transmission from this H5N5 case. Angela Rasmussen, a virologist at the Vaccine and Infectious Disease Organisation, stated that H5N5, like H5N1, does not transmit well between people, according to The BMJ. Ian Jones, a virologist at the University of Reading, further added that the H5N5 infection in Washington had "almost no chance of spreading any further," with the risk to the general population being "essentially nil".

• Preventative Measures and Recommendations: Health authorities urge individuals, especially those with backyard poultry, to practice strict biosecurity measures. This includes avoiding contact with sick or dead birds and reporting any suspected illnesses in poultry to the Washington State Department of Agriculture, as advised by the Washington State Department of Health. The CDC also recommends getting a seasonal flu vaccine, which, while not preventing bird flu, can reduce the risk of co-infection and potential viral reassortment.

• Global Context of Avian Influenza: Avian influenza viruses are widespread globally, with the FAO reporting 954 outbreaks in animals across 38 countries since October 1, 2025, including four H5N5 outbreaks. The UK Health Security Agency noted that both H5N1 and H5N5 were detected in wild and kept birds in Great Britain last year, highlighting the ongoing presence of these strains in avian populations.