The First Human Avian Influenza A(H5N5) Case: A Fatal Infection in Washington, 2025

This page summarizes a report in CDC's MMWR by the Washington State Department of Health, local health departments, hospitals, universities, agriculture agencies and CDC. Day numbers count from the patient's first symptoms.

Highly pathogenic avian influenza (HPAI) A(H5) viruses of clade 2.3.4.4b have circulated in U.S. wild birds along migratory flyways since 2022, including in Washington, where infections in backyard flocks have been found every year. Seventy human A(H5) cases, most of them mild, had been reported in the United States since 2024, and Washington had earlier identified 14 human A(H5N1) cases.

In November 2025, Washington reported the first human infection with HPAI A(H5N5) found anywhere in the world.

The patient's illness

The early negative results meant isolation precautions were applied inconsistently. They were not in place consistently until the ninth day of inpatient care.

Where the virus came from

The property. The patient lived on a rural property of several acres visited by wild birds, including waterfowl. One family member shared the house, and another lived in a separate home on the property. Through interviews with others on the patient's behalf, Grays Harbor County Public Health learned that the patient owned and cared for a free-range backyard flock of 25 dabbling ducks and about 30 chickens, with several basins set into the ground for the birds' watering and enrichment.

In the week before falling ill, the patient tended the flock daily, handled eggs, and cleaned and filled the basins with a hose, all without personal protective equipment (PPE). There were no other animals, including livestock, and no known contact with raw dairy.

Two sick ducks. On day 2, two ducks looked ill. A household member caged them; they died overnight and were disposed of on the property. The patient did not handle them, and daily care of the flock stopped when the patient fell ill.

The flock. On day 21 state and federal agriculture officials swabbed every duck and pooled swabs from the chickens. The flock looked healthy, but all the ducks gave weak detections on at least one avian influenza PCR assay; the chickens' pooled sample was negative. The flock was depopulated on day 22. At the National Veterinary Services Laboratories, six ducks tested positive for influenza A, all with Ct values above 35, too weak for virus isolation or direct sequencing.

The environment. Also on day 21, the state health department sampled a feather, suspected duck feces in the holding cage, and sediment from the bottom of one watering basin. The sediment was presumptive positive for A(H5) clade 2.3.4.4b, and the National Veterinary Services Laboratories confirmed HPAI A(H5), isolated the virus and typed it as A(H5N5), genotype A6, sequencing six of its eight genes (day 39).

The match. Six of eight gene segments from the sediment, and a partial neuraminidase segment from one duck (Ct 35.07), were highly similar genetically to the patient's virus.

Wild bird surveillance had not found A(H5N5) genotype A6 in the U.S. Pacific Flyway. Even so, the most likely source was the virus arriving in the flock's environment with wild waterfowl, then amplified by the birds on the property.

Following the contacts

Anyone possibly exposed to the patient, the flock or its surroundings was watched for influenza symptoms until 10 days after their last exposure, mostly through REDCap databases sending automatic daily text questionnaires. Fifteen developed compatible symptoms; none tested positive for influenza.

• Health departments and CDC drew up a tiered risk assessment for health care workers, based on setting and PPE use, for hospitals worried about staff shortages. It let exposed staff keep working under symptom monitoring and limited new exposures. No health care worker was infected.
• Of seven family members identified, including two living on the property, six agreed to weekly phone monitoring. During the final hospitalization only family could visit, with hospital-supplied PPE including respirators that were not fit-tested. More relatives appeared in visitor logs without contact details, so the total number of exposed family members is unknown.
• No family member was infected, despite long exposure to the patient and the property. One household member touched the sick and dead ducks and never had symptoms.
• The investigation fell during respiratory virus season, while several monitored people developed symptoms, which made it harder.

Lessons

• Risk to the public remains low. Human-to-human spread of avian influenza A has been reported only rarely worldwide, and never in the United States. Risk rises with direct, or close and prolonged, contact with infected animals without recommended PPE. Still, three U.S. human A(H5N1) cases have had no clear source.
• Ask about exposures. Clinicians seeing acute respiratory illness, especially severe illness needing hospital care, should ask about contact with sick or dead animals or their surroundings, handling or eating raw animal products, and contact with confirmed or suspected human cases.
• A negative upper respiratory test does not rule it out. Early negative upper respiratory results have been described in three similar hospitalized A(H5N1) patients with lower respiratory disease. When avian influenza is suspected in severe respiratory illness, collect upper and lower respiratory specimens for RT-PCR at a public health laboratory, and repeat testing.
• Act on suspicion. Isolate at once, start antivirals promptly, notify public health early, and use genomic sequencing to trace transmission.
• Report sick or dead animals to animal health authorities, both for surveillance and to cut human exposure.

Sources

• Kibiger L, Oltean HN, Leitz L, et al. "Fatal Human Case of Highly Pathogenic Avian Influenza A(H5N5) in a Backyard Flock Owner — Washington, November 2025." MMWR 75(17). https://www.cdc.gov/mmwr/volumes/75/wr/mm7517a2.htm
• The report's figure is not reproduced, because the report was prepared jointly by state and county agencies, hospitals, universities and CDC.