Notification from the Los Angeles County Department of Public Health
Notification from the Los Angeles County Department of Public Health
CDC/LAC DPH Health Advisory:
Accelerated Subtyping of Influenza A in Hospitalized Patients
January 17, 2025
The Centers for Disease Control and Prevention (CDC) has issued a Health Advisory recommending that clinicians and laboratories expedite subtyping of influenza A positive specimens from hospitalized patients, especially those in the ICU. In alignment with this CDC guidance, Los Angeles County Department of Public Health (LAC DPH) is enhancing surveillance measures for avian influenza (H5N1), otherwise known as H5 bird flu, to ensure timely identification and response to potential human infections.
All hospitalized patients suspected of having influenza should be tested within 24 hours of admission using a diagnostic test capable of providing influenza subtyping. For facilities without subtyping capabilities, testing can be ordered through a commercial laboratory. The Los Angeles County Public Health Laboratory (PHL) is able to offer influenza A subtyping for ICU patients for Los Angeles County facilities without subtyping capabilities.
Clinicians should assess patients for H5 bird flu risk factors and notify the LAC DPH immediately in H5 bird flu is suspected. Influenza A specimens from such patients should be tested for H5 bird flu in consultation with LAC DPH, either through PHL or alternatively, a commercial laboratory that performs H5 bird flu specific testing.
Key Recommendations
LAC DPH requests the following actions for all hospitalized patients with symptoms of influenza:
Collecting and Subtyping Specimens
  • Clinicians:
    • Test for influenza in all patients with suspected infection within 24 hours of hospital admission. Where available, order a diagnostic test that can provide influenza A subtyping results.
    • For ICU patients, if subtyping is not available at your facility, call DPH to arrange subtyping of influenza A positive specimens from ICU patients.
    • Assess patients for exposure to sick animals, dairy cattle, poultry, wild birds or their environments, and consumption of raw milk or raw meat. Patients with an exposure history suggestive of H5 bird flu should be reported immediately to LAC DPH and should be tested using an H5 bird flu specific test in consultation with LAC DPH.

  • Laboratories:
    • If your facility has the capability, perform subtyping on all influenza A-positive specimens from hospitalized patients within 24 hours of admission
      • During subtyping, if the influenza A positive specimen is: untypeable, or type is NOT consistent with seasonal flu variants (H1, H1PDM09, or H3), submit the specimen within 24 hours to PHL for further testing.
    • If subtyping is not available at your facility, call DPH to arrange subtyping of influenza A positive specimens from ICU patients at the PHL. Only influenza A-positive specimens that were previously tested using molecular methods can be tested at the PHL.
      • Alternatively, there are a few commercial laboratories with subtyping capabilities that may be used to expedite specimen processing.
Reporting
Notify Public Health immediately for patients with high-risk exposure and influenza symptoms or unsubtypable specimens.
Los Angeles County DPH Acute Communicable Disease Control:
  • Weekdays 8:30 am–5:00 pm: call 213-240-7941.
  • After-hours: call 213-974-1234 and ask for the physician on call.
Long Beach Health and Human Services:
  • Weekdays 8:00 am-5:00 pm: call 562-570-4302.
  • After hours: call the duty officer at 562-500-5537.
Pasadena Public Health Department:
  • Weekdays 8:00 am-5:00 pm: call 626-744-6089.  
  • After hours: call 626-744-6043.
Visit the LAC DPH Avian Influenza A (H5N1) in Humans website for related resources, including FAQs on influenza A subtyping. 
Read the CDC Health Advisory
You can also copy and paste this link into your browser: https://www.cdc.gov/han/2025/han00520.html
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