Washington State Confirms World's First Human H5N5 Bird Flu Infection

A Washington state resident is suffering from severe illness after becoming the first human globally confirmed to be infected with the H5N5 strain of avian influenza. The patient, an older adult with underlying health conditions, was hospitalized earlier this month in Grays Harbor County with a high fever, confusion, and respiratory distress. This marks a significant development as H5N5 has previously only been detected in animals.

The Washington State Department of Health confirmed the diagnosis, stating the "severely ill" man was found to have H5N5, a subtype of avian influenza typically carried by wild birds such as ducks and geese. Authorities believe the most likely source of exposure was the man's mixed backyard flock of domestic poultry, which had contact with wild birds. The patient remained hospitalized as of last week, with investigations ongoing into the exact transmission pathway.

While H5N5 is a novel human infection, other avian influenza strains, notably H5N1, have caused human cases in the United States. The Centers for Disease Control and Prevention (CDC) has reported over 70 human H5N1 cases in the US since 2024, predominantly among dairy and poultry workers, with one death recorded in Louisiana in January 2025. Experts note that H5N5 viruses appear to behave similarly to H5N1 from a human health perspective.

The current H5N1 outbreak has been widespread in wild birds, poultry, and dairy cattle across the US, leading to concerns among public health officials about viral evolution. Virologists emphasize that each human infection presents an opportunity for the virus to mutate, potentially becoming more transmissible. Despite these concerns, health agencies, including the CDC, maintain that the risk to the general public from avian influenza remains low.

Public health officials are actively monitoring the situation and stress the importance of a "One Health" approach, integrating human, animal, and environmental health. They advise individuals to avoid contact with sick or dead birds and to practice good hygiene, especially those who work with poultry or other animals. The Washington State Department of Health continues to investigate the case and monitor for any further spread.