First Human Case of Influenza A(H5N5) Virus Infection Confirmed in Washington State

Situation summary

A Washington resident hospitalized since early November was confirmed to have influenza A(H5N5) virus infection on November 13th and died on November 21, 2025. This is the first known case of influenza A(H5N5) infection in humans. Testing by Washington State Department of Health detected avian influenza virus in the patient's backyard flock environment, indicating likely exposure from their backyard flock of mixed domestic birds, their environment, or wild birds.

The risk of highly pathogenic avian influenza (HPAI) infection for the general public remains low. However, the panzootic of HPAI viruses in wild birds has resulted in outbreaks among commercial poultry and backyard flocks and has spread to infect wild terrestrial and marine mammals as well as domesticated animals. Therefore, people with work or recreational exposures to HPAI infected animals are at increased risk of infection. Clinicians should consider the possibility of HPAI in persons showing compatible signs and symptoms with relevant exposure history.

For details on assessment, testing, and management of influenza A (H5), see the Provider Alert from Washington State Department of Health (November 18, 2025).

Key points

• Obtain animal exposure history for all patients with suspected or confirmed influenza. PHSKC recommends adding screening questions to the electronic medical record (EMR).  
  • Assess all patients with suspected or confirmed influenza for exposure to: 
  • Sick or dead animals, wild or domestic, or their environment 
  • Wild, captive, and livestock animals, including poultry and cattle 
  • Consumption or handling of raw animal products (raw cow milk and products made with raw cow milk, and raw meat-based pet foods) 
  • Recent close contact (within six feet) with a symptomatic person suspected or confirmed to have avian influenza 
• Test all hospitalized patients with compatible influenza symptoms and exposure history within 24 hours of presentation
  • A negative influenza test does not rule out avian influenza. 
  • Collect lower respiratory tract specimens from patients with severe respiratory disease, if possible, in addition to NP, OP, or conjunctival swabs for influenza testing. Lower respiratory tract specimens have a higher yield for detecting HPAI (e.g. HPAI A(H5N1) and A(H7N9). 
• All positive influenza A specimens should be submitted for subtyping (tested to determine the subtype of influenza A, i.e., A(H1N1)pdm09 or A(H3N2)) at your facility's clinical or commercial laboratory. If subtyping is not available through your facility, specimens should be submitted to the Washington State Public Health Laboratories for subtyping 
• Immediately report the following to Public Health at 206-296-4774: 
  • All suspected and confirmed cases of novel influenza, including H3 and H5, regardless of influenza test results. 
  • All influenza A specimens that result as “unsubtypeable” (usually meaning the test result does not detect seasonal influenza).