U.S. confirms first human death from rare H5N5 Avian Flu strain

Health authorities in Washington State have confirmed the world’s first human death caused by the H5N5 strain of avian influenza, marking a significant and concerning milestone in the ongoing battle against bird flu.

David Corredor

Health authorities in Washington State have confirmed the world’s first human death caused by the H5N5 strain of avian influenza, marking a significant and concerning milestone in the ongoing battle against bird flu. The patient, described as an older adult with underlying health conditions, died on November 21 after being hospitalized earlier this month with severe flu-like symptoms, including high fever, respiratory distress, and confusion.

• According to the Washington State Department of Health, laboratory tests conducted by the University of Washington and verified by the U.S. Centers for Disease Control and Prevention (CDC) confirmed the infection as H5N5—a strain previously detected only in birds and mammals, but never before in humans.
• This case represents the first recorded human infection globally with this variant.

Officials believe the source of exposure was the patient’s backyard flock of mixed domestic poultry, which had contact with wild birds. Environmental sampling around the flock detected traces of avian influenza, supporting this theory. Investigations into the exact transmission route are ongoing, but authorities emphasize that there is no evidence of human-to-human transmission and that the overall risk to the public remains low.

• The emergence of H5N5 in humans raises questions about the virus’s potential to adapt and spread.
• While avian influenza viruses have circulated among bird populations for decades, recent years have seen an increase in infections among mammals, including cattle and other species.
• The dominant strain in recent U.S. outbreaks has been H5N1, which has caused more than 70 human cases nationwide since early 2024, mostly linked to direct contact with infected animals.

Experts warn that each human infection provides an opportunity for the virus to mutate, potentially increasing its transmissibility among people. However, for now, H5N5 appears to behave similarly to other avian influenza strains: it spreads primarily through contact with infected birds or contaminated environments. Symptoms in humans can range from mild respiratory illness to severe complications, particularly in older individuals or those with pre-existing health conditions.

Public health agencies urge poultry owners and wildlife handlers to take precautions, including avoiding contact with sick or dead birds, wearing protective gear, and practicing strict hygiene. Cooking poultry products thoroughly remains an effective measure to prevent infection. While the risk of a pandemic from H5N5 is considered low, health authorities continue to monitor the situation closely.