On Oct. 20, 2024, the Washington State Department of Health announced that four agricultural workers tested positive for avian influenza after working with infected poultry at a commercial egg farm in Franklin County. The individuals experienced mild symptoms and were provided with antiviral medication. Testing of additional individuals on the farm was pending.

These were the first presumed human cases of H5 virus under investigation in Washington state. The cases took place at a farm that was the site of an avian influenza outbreak in chickens. About 800,000 birds were euthanized after test results by the Washington State Department of Agriculture on Oct. 15 showed that they were infected with avian influenza.

Washington was the sixth state to identify a human infection of H5N1. H5N1 highly pathogenic avian influenza (HPAI) has caused ongoing multistate outbreaks in poultry, dairy cattle, and wildlife.