What to know
- This page provides information for clinical and public health laboratories on testing for novel influenza A viruses, including for identification of avian influenza A(H5N1) virus in patient specimens.
- ÐÇ¿ÕÓéÀÖ¹ÙÍø recommends specific surveillance efforts by state and local health departments, hospitals, and clinicians among people at increased risk of exposure to novel influenza A viruses.
- ÐÇ¿ÕÓéÀÖ¹ÙÍø recommends expedited subtyping of all influenza A specimens obtained from hospitalized patients and increased efforts at clinical laboratories to identify non-seasonal influenza viruses.
- This can help prevent delays in identifying human infections with avian influenza A(H5N1) viruses or other novel influenza viruses.
Testing at clinical laboratories
Background on novel influenza A virus testing
Most influenza tests ordered in clinical settings do not distinguish avian influenza A, including influenza A(H5) viruses from seasonal influenza A viruses; a positive result simply confirms influenza A virus infection. Using tests that identify the seasonal influenza A virus subtype helps identify the subtype.
If a test result is positive for influenza A virus but negative for seasonal influenza A virus subtypes [i.e., A(H1) and A(H3)], the virus detected might be a novel influenza A virus, such as avian influenza A(H5), and specimens should be prioritized for shipment to a public health laboratory for additional testing.
Additionally, the Food and Drug Administration offers a list of influenza A typing and subtyping tests.
Services like diagnostic and subtype testing that are reasonable and necessary to diagnose illness are covered in most cases by both public and private health insurers.
Test protocols for novel influenza A virus testing
- Subtype and send respiratory specimens that are positive for influenza A but negative for seasonal influenza A virus subtypes [i.e., negative for A(H1) and A(H3)] to a public health laboratory as soon as possible and at the latest within 24 hours of obtaining the results – especially for critically ill, hospitalized patients.
- If influenza A virus subtyping is not available at the hospital or the clinical laboratory of the treating facility, public health officials should be notified, and arrangements made for influenza A virus-positive respiratory specimens to be subtyped at a public health laboratory or a commercial laboratory with this testing capability.
- Specimens should be clearly linked to clinical information from the patient, such as severity of illness, exposure history, etc, to ensure specimens from severely ill and ICU patients are prioritized.
- Do not batch specimens for consolidated or bulk shipment to the public health laboratory if that would result in shipping delays for any such specimen.
- Immediately contact the if a positive result for any novel influenza A virus is obtained using a laboratory developed test (LDT) or another novel influenza A subtyping test to initiate important time-critical actions.
Preventing delays in identifying human infections with avian influenza A(H5N1) viruses
ÐÇ¿ÕÓéÀÖ¹ÙÍø recommends expedited subtyping of all influenza A specimens obtained from hospitalized patients and increased efforts at clinical laboratories to identify non-seasonal influenza viruses. Clinicians and laboratorians are reminded to test for influenza in patients with suspected influenza and, to expedite subtyping of influenza A-positive specimens obtained from hospitalized patients, particularly those in an intensive care unit (ICU). This can help prevent delays in identifying human infections with avian influenza A(H5N1) viruses, support optimal patient care and timely infection control and case investigations.
Testing at state public health laboratories
Testing protocols for novel influenza A viruses at Public Health Laboratories:
- The ÐÇ¿ÕÓéÀÖ¹ÙÍø Human Influenza Real-Time RT-PCR Flu Diagnostic Panel (ÐÇ¿ÕÓéÀÖ¹ÙÍø Flu rRT-PCR Dx Panel) testing algorithms should be used as described in the package insert to rule out seasonal influenza A or B virus infection.
- All state public health laboratories should use the ÐÇ¿ÕÓéÀÖ¹ÙÍø Flu rRT-PCR Dx Panel to screen specimens for InfA, InfB, and RP.
- State public health laboratories should test all InfA-positive specimens with the ÐÇ¿ÕÓéÀÖ¹ÙÍø Influenza A Subtyping kit using all primer/probe sets: H3, pdmInfA and pdmH1. Detailed guidance for testing can be found in the influenza surveillance diagnostic testing algorithm disseminated by the Association of Public Health Laboratories. An aliquot of the sample should be reserved in case there is a need to ship it to ÐÇ¿ÕÓéÀÖ¹ÙÍø.
- For specimens collected from patients with suspected infection with HPAI A(H5) viruses, testing should be performed using the ÐÇ¿ÕÓéÀÖ¹ÙÍø H5 primer/probe set. Specimens that are positive or inconclusive for A(H5) virus by rRT-PCR at the state health department should be sent to ÐÇ¿ÕÓéÀÖ¹ÙÍø Influenza Division for additional testing as soon as possible.
When to Notify ÐÇ¿ÕÓéÀÖ¹ÙÍø
ÐÇ¿ÕÓéÀÖ¹ÙÍø should be notified immediately if any human specimens test positive for any novel influenza A virus [e.g., LPAI or HPAI A(H7N9), HPAI A(H5N1), HPAI A(H5N6) or other avian A(H5) viruses, or variant influenza A viruses* such as A(H3v)], and specimens should be shipped to ÐÇ¿ÕÓéÀÖ¹ÙÍø for confirmatory testing.
Public health officials should contact ÐÇ¿ÕÓéÀÖ¹ÙÍø immediately if they get unsubtypeable results when testing an influenza A virus positive specimen. Complete influenza A virus subtyping assays within 24 hours of receipt and report results to ÐÇ¿ÕÓéÀÖ¹ÙÍø, as required.
* Influenza A viruses that normally circulate in pigs are termed "variant viruses" when identified in infected humans.
Specimen collection
ÐÇ¿ÕÓéÀÖ¹ÙÍø has guidance for clinicians and public health professionals in the United States on appropriate specimen collection and diagnostic testing for patients who might be infected with novel influenza A viruses associated with severe human disease or with potential to cause severe human disease.
Shipment of specimens to ÐÇ¿ÕÓéÀÖ¹ÙÍø
Specimens that are confirmed at the state public health lab or that test presumptive positive for novel influenza A virus at the state public health laboratory should be sent to ÐÇ¿ÕÓéÀÖ¹ÙÍø, Influenza Division, Virology Surveillance and Diagnosis Branch Laboratory for confirmatory or additional testing. ÐÇ¿ÕÓéÀÖ¹ÙÍø still requires that states that can confirm A(H5) viruses at the state public health lab send specimens to ÐÇ¿ÕÓéÀÖ¹ÙÍø for additional virologic characterization. Laboratories should not attempt to isolate novel influenza A viruses using viral culture.