Health Advisory: Subtyping of Influenza A Recommended for Hospitalized Patients

January 29, 2025

This is a Health Alert from the Snohomish County Health Department regarding CDC and WA DOH recommendations for increased influenza subtyping in hospitalized patients.  

Recently, the Centers for Disease Control and Prevention (CDC) issued a Health Advisory recommending influenza A testing for all hospitalized patients with suspected influenza and also recommending expedited influenza subtyping for influenza A-positive specimens. This was followed by a similar advisory from the Washington DOH. 

SCHD partners should be aware of the following:  

• The Snohomish County Health Department will continue to immediately report the following to the Washington State Department of Health (DOH) Office of Communicable Disease Epidemiology (OCDE):  
  1. Any suspected or confirmed cases of highly pathogenic avian influenza A (HPAI) H5N1 (hereafter: HPAI A(H5N1)) 
  2. Any report of an unsubtypeable influenza A specimen 
• The Washington State Public Health Laboratories (PHL) can test:  
  1. Any unsubtypeable influenza A specimen (current practice) 
  2. Any specimen from a person suspected of having of HPAI A(H5N1) (current practice) 
  3. As capacity permits, PHL may be able to test influenza A positive specimens from hospitalized patients that have NOT been subtyped at a clinical or commercial lab (new recommendation – see below for details) 

Current Situation 

Seasonal influenza activity is currently high in Washington State, and across the U.S. In addition to seasonal influenza activity, sporadic human cases of highly pathogenic avian influenza A (HPAI) H5N1 have been identified across the U.S., associated with the ongoing H5N1 outbreak in wild birds, poultry, dairy cows, and other wild and domestic animals. 

The first human cases of HPAI A(H5N1) were identified in Washington State in October 2024 among people who had close, prolonged contact with infected poultry or their environment. While the human cases identified in Washington have been mild, at least one fatal US case of H5N1 has been identified in a Louisiana patient who was admitted to an ICU.   

Clinicians and clinical laboratories are being asked to subtype all influenza A-positive specimens in hospitalized patients, so that potential cases of HPAI A (H5N1) can be quickly identified. 

Actions Requested 

Testing  

It is recommended that hospital healthcare providers and clinical laboratories subtype all influenza A positive specimens in hospitalized patients to H1/H3 v unsubtypeable, especially patients in the Intensive Care Unit (ICU).  

• If possible, subtyping tests should be performed in the hospital clinical laboratory or sent to a commercial laboratory. The FDA has a list of available approved influenza tests. 
• If a patient tests positive for influenza via a rapid diagnostic test, providers are encouraged to collect a new specimen that allows for influenza subtyping. 
• If influenza A virus subtyping for hospitalized patients is NOT available through clinical or commercial laboratories, the Washington PHL may have capacity to offer subtyping for influenza A positive specimens on a limited basis. Within PHL, specimens will be prioritized in the following manner:  
  1. Influenza A-positive specimens from hospitalized patients with known exposure to sick or deceased animals, raw animal products, or suspected or confirmed HPAI A(H5N1) patients 
  2. Subtyped Influenza A specimens with an unsubtypeable result 
  3. Influenza A specimens that have NOT been subtyped from a patient admitted to an ICU 
  4. All other hospitalized patients testing positive for influenza A whose specimens have NOT been subtyped. 

Subtyping is especially important in the following groups of patients:  

• Patients admitted to an ICU 
• Influenza A-positive patients with a history of exposure to sick or deceased animals, raw animal products, or suspected or confirmed HPAI A(H5N1) patients 

Notification 

• ALL providers should report suspected novel or avian influenza cases to the Snohomish County Health Department immediately by calling 425-339-3503.  
• Clinicians, facilities, and laboratories should CONTINUE to immediately notify the Snohomish County Health Department of any unsubtypeable influenza A specimens according to notifiable conditions rules.  
• Laboratories should CONTINUE to submit unsubtypeable specimens to PHL for additional typing according to testing guidance for influenza within 24 hours of identification. 

Infection Prevention

• Healthcare providers/infection preventionists should implement appropriate infection control measures when influenza is suspected or confirmed. 
• If HPAI A(H5N1) virus infection is suspected or confirmed in a hospitalized patient:  
  1. Providers should IMMEDIATELY place the patient in an airborne infection isolation room with negative pressure 
  2. Providers should implement standard, contact, and airborne precautions with eye protection (goggles or face shield). 

Background

CDC has routinely recommended influenza testing for hospitalized patients with suspected influenza. In light of the ongoing HPAI A(H5N1) virus animal outbreak in the United States, CDC and WA DOH now recommend subtyping of all influenza A virus-positive specimens from hospitalized patients on an accelerated basis. This subtyping effort is part of a comprehensive national strategy to identify severe human infections with HPAI A(H5N1) viruses, in addition to characterizing seasonal influenza viruses in a timely fashion. 

Enhanced influenza A virus subtyping of specimens from hospitalized patients, especially from those in an ICU, can help avoid potential delays in identifying human infections with HPAI A(H5N1) viruses. Such delays are more likely while seasonal influenza activity is high, as it is now, due to high patient volumes and general burden on healthcare facilities. 

CDC still considers the risk from HPAI A(H5N1) viruses to the public to be low but is closely monitoring this dynamic situation. At this time, while seasonal influenza levels are high nationally, nearly all people who are currently hospitalized with influenza A virus infections likely have seasonal influenza. 

Contact 

For additional questions, or to report suspect cases:

• Call 425-339-3503 to reach the Snohomish County Health Department Communicable Disease Surveillance & Response Program by phone. SCHD can help arrange sample collection and testing at the Washington State Public Health Laboratories. Staff can provide guidance on collecting the below samples: 

1. A nasopharyngeal swab collected in viral transport medium for testing at WA PHL 
2. .Patients with conjunctivitis should also have a conjunctival swab collected in viral transport medium for testing at WA PHL 

Resources

• WA DOH Influenza Reporting and Investigation Guideline- Novel and Unsubtypable Influenza 
• Influenza Virus Testing at the Washington Public Health Laboratories (WAPHL) 
• Avian Influenza | Washington State Department of Health 
• WA DOH Health Alert: Presumptive Positive Human Cases of Avian Influenza Under Investigation in Washington; Recommendations for Human Health Investigation and Response 
• CDC: Clinical Overview of Evaluating and Managing Patients Exposed to Birds Infected with Avian Influenza A Viruses of Public Health Concern  
• CDC: H5N1 Bird Flu: Current Situation  
• CDC: Health Alert Network (HAN) - 00520 | Accelerated Subtyping of Influenza A in Hospitalized Patients  
• CDC: Interim Guidance on the Use of Antiviral Medications for Treatment of Human Infections with Novel Influenza A Viruses Associated with Severe Human Disease  
• CDC: Interim Guidance for Infection Control Within Healthcare Settings When Caring for Confirmed Cases, Probable Cases, and Cases Under Investigation for Infection with Novel Influenza A Viruses Associated with Severe Disease  
• CDC: Interim Guidance on Specimen Collection and Testing for Patients with Suspected Infection with Novel Influenza A Viruses Associated with Severe Disease or with the Potential to Cause Severe Disease in Humans