12/27/2024 Considerations for Use of Influenza A(H5) Subtyping Tests by Clinical Laboratories

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  • Level: Laboratory Advisory
  • Audience: Clinical Laboratory Professionals
LOCS: Laboratory Outreach Communication System

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The design and use of influenza A(H5) subtyping in vitro diagnostic (IVD) devices offered as laboratory developed tests (LDTs) among clinical diagnostic laboratories has expanded nationally to support early detection and public health response to human cases of A(H5) detected in the United States. The U.S. Centers for Disease Control and Prevention (CDC) continues to distribute an FDA 510k-cleared IVD influenza A(H5) assay to state and jurisdictional public health laboratories to test patients for influenza A(H5) virus. CDC is also aware of recent development and use of IVDs offered as LDTs independent of state and jurisdictional public health laboratories to diagnose influenza A(H5) virus in patient specimens.

While CDC supports the development and use of additional tests to subtype A(H5) virus in clinical samples, we would like to highlight some key considerations below:

It is critical to immediately contact the state, local, territorial, or tribal public health authority if a positive result for influenza A(H5) virus is obtained using an LDT to initiate important time-critical actions.

  • Positive results must be immediately reported to the proper state or jurisdictional public health authority through existing processes to ensure that clinical management, antiviral treatment, isolation recommendations and public health investigations are initiated promptly following detection of each case.
  • Contact tracing, symptom monitoring, additional testing, and human and animal health investigations require immediate action by the state, local, territorial, or tribal public health authority. These steps are essential to evaluate if person-to-person transmission has occurred, to reduce risk of onward transmission and to prevent additional cases among people with related animal or environmental exposures.
  • Influenza A(H5) positive samples must be immediately shipped to a public health laboratory for virus characterization and risk assessment. The testing laboratory should consult with the state, local, territorial, or tribal public health authority to discuss appropriate shipping and sample handling. Additional testing is an essential step in the public health response, enabling identification of genetic changes in viruses that may increase transmissibility and disease severity in humans, reduce susceptibility to antivirals, impact diagnostic assay performance and therapeutic recommendations, or reduce A(H5) candidate vaccine virus cross-protection—all of which are critical for overall public health preparedness efforts.
  • It is also critical for those developing and utilizing A(H5) subtyping LDTs to have established reporting processes with state, tribal, local, and territorial (STLT) public health departments and CDC to ensure that both national and international reporting requirements are met following detection of A(H5) in a human. Because A(H5) is a reportable condition via state laws, immediate reporting to STLT public health officials is required. Further, A(H5) is classified as a nationally notifiable disease (National Notifiable Diseases Surveillance System (NNDSS) - Health, United States) and under the International Health Regulations (IHR) of 2005, the U.S. is required to report human cases of A(H5) to the World Health Organization (International Health Regulations (2005) – Third edition). This immediate reporting requirement to WHO (within 24 hours of case confirmation) is performed by the U.S. National IHR Focal Point located at the CDC. Emergency contact information for health departments is available at the Council of State and Territorial Epidemiologists website at https://www.cste.org/page/EpiOnCall. Additional points of contact are also available on the Resources tab on the main webpage (www.cste.org).
  • Clinicians and other health care providers should carefully consider whether the patient meets epidemiologic, clinical, and public health response criteria (see below) prior to ordering and performing an A(H5) subtyping test. As the fall/winter influenza season progresses, testing should be conducted in the context of a testing algorithm that first rules out seasonal influenza A virus when specific criteria for A(H5) testing are not met. The CDC recommends testing an individual for A(H5) when the following criteria are met:

Epidemiological Criteria*
Persons with recent exposure (within 10 days) to highly pathogenic avian influenza (HPAI) A(H5N1) virus through one of the following:

- Exposure to HPAI A(H5N1) virus-infected birds or other animals defined as follows:

  • Close exposure (within six feet) to birds or other animals, with confirmed avian influenza A(H5N1) virus infection. Bird or other animal exposures can include, but are not limited to handling, slaughtering, defeathering, butchering, culling, milking, or preparing animals for consumption, or consuming uncooked or undercooked food or related uncooked food products, including unpasteurized (raw) milk,

OR

  • Direct contact with surfaces contaminated with feces, unpasteurized (raw) milk or other unpasteurized dairy products, or bird or animal parts (e.g., carcasses, internal organs) from infected birds or other animals,

OR

  • Visiting a live bird market with confirmed HPAI A(H5N1) virus infections in birds or associated with a case of human infection with HPAI A(H5N1) virus.

- Exposure to an infected person – Close (within six feet) unprotected (without use of respiratory and eye protection) exposure to a person who is a confirmed, probable, or symptomatic suspected case of human infection with HPAI A(H5N1) virus (e.g., in a household or healthcare facility).

- Laboratory exposure (unprotected exposure to HPAI A(H5N1) virus in a laboratory)

AND

Clinical Criteria*
Persons with signs and symptoms consistent with acute upper or lower respiratory tract infection, conjunctivitis, or complications of acute respiratory illness without an identified cause. In addition, gastrointestinal symptoms such as diarrhea are often reported with HPAI A(H5N1) virus infection.

OR

Public Health Response Criteria*
Testing of asymptomatic persons for HPAI A(H5N1) virus infection is not routinely recommended. However, for the purpose of public health investigations as part of the response to the ongoing H5N1 situation, in consultation with state and local health departments, a test for influenza A(H5) virus may be offered to asymptomatic workers with high risk of exposure to HPAI A(H5N1) virus [e.g., exposed to animals infected with HPAI A(H5N1) virus who reported not wearing recommended PPE or who experienced a breach in recommended PPE], or asymptomatic close contacts of a confirmed case of HPAI A(H5N1) virus infection.

*See for more details: Highly Pathogenic Avian Influenza A(H5N1) Virus: Interim Recommendations for Prevention, Monitoring, and Public Health Investigations | Bird Flu | CDC

For those laboratories contemplating or currently utilizing A(H5) LDTs, we thank you for reviewing these considerations and welcome your feedback to ensure that we enhance our collective efforts to rapidly detect and respond to human cases of A(H5).

We encourage you to share this message widely with your network(s).

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