Health Advisory: Subtyping of Influenza A Recommended for Hospitalized Patients

This is a Health Alert from the Washington State Department of Health (DOH) regarding CDC recommendations for increased influenza subtyping in hospitalized patients. 

Last week, 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 recommends expedited influenza subtyping for influenza A-positive specimens.  

Public health partners should be aware of the following: 

  • Local Health Jurisdictions (LHJs) in Washington should continue to immediately report the following to the Washington State Department of Health (DOH) Office of Communicable Disease Epidemiology (OCDE):
    • Any suspected or confirmed cases of highly pathogenic avian influenza A (HPAI) H5N1 (hereafter: HPAI A(H5N1))
    • Any report of an unsubtypeable influenza A specimen
  • The Washington State Public Health Laboratories (PHL) can test:
    • Any unsubtypeable influenza A specimen (current practice)
    •  Any specimen from a person suspected of having of HPAI A(H5N1) (current practice)
    • 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)

To increase healthcare provider awareness around these updates, we have also drafted a Provider Alert (PDF).

Current Situation 

Seasonal influenza activity is currently high in Washington State, and across the US. In addition to seasonal influenza activity, sporadic human cases of highly pathogenic avian influenza A (HPAI) H5N1 have been identified across the US, 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

  • Recommend that hospital healthcare providers and clinical laboratories subtype all influenza A positive specimens in hospitalized patients, 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.
    • 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. 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. 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.
  •   Advise healthcare providers that 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

  • LHJs should CONTINUE to IMMEDIATELY notify WA DOH about the following notifiable conditions:
    • Any suspected human cases of novel or avian influenza
    • Influenza A-positive specimens that are reported as unsubtypeable
  • Encourage ALL providers to report suspected novel or avian influenza cases to their LHJ immediately.
  • Clinicians, facilities, and laboratories should CONTINUE to immediately notify their LHJ of any unsubtypeable influenza A specimens according to notifiable conditions rules.  
    • Laboratories should CONTINUE to submit these specimens to PHL for additional typing according to testing guidance for influenza within 24 hours of identification.

Investigation

  • LHJs and Tribal Health Partners should investigate any patients with unsubtypeable influenza A results for risk factors of avian influenza including: 
    • Exposure to wild animals
    • Exposure to domestic animals including livestock (e.g., poultry, cattle) and pets (e.g., cats)
    • Consumption of raw animal products (e.g., raw cow milk and raw cow milk products, including use of raw meat-based pet food),
    • Recent close contact with a symptomatic person with a probable or confirmed case of HPAI A(H5N1). 
    • See DOH Investigation Guidelines for Influenza – Novel or Unsubtypeable Strain for additional details.
  •  Report these risk factors to the WA DOH Influenza surveillance team.

Infection Prevention

  • Remind healthcare providers/infection preventionists to 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:
    • Direct providers to IMMEDIATELY place the patient in an airborne infection isolation room with negative pressure 
    • Advise providers to 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.

Resources

Contact

To report suspected cases, or for any other questions, please contact your Local Health Jurisdiction