CDC H1N1 Flu | Interim Recommendations for Clinical Use of Influenza Diagnostic Tests

Interim Recommendations for Clinical Use of Influenza Diagnostic Tests During the 2009-10 Influenza Season
September 29, 2009, 6:00 PM ET

Objective
To provide updated interim recommendations on influenza diagnostic testing for clinicians treating patients with suspected 2009 H1N1 influenza virus infection and to assist clinicians with testing decisions for the 2009-10 influenza season 1. These recommendations may be further revised as more information becomes available. These recommendations also can be adapted according to local epidemiologic and surveillance data and other state and local considerations. Clinical judgment is always an important part of testing and treatment decisions.

Summary Points
Most patients with clinical illness consistent with uncomplicated influenza who reside in an area where influenza viruses are circulating do not require diagnostic influenza testing for clinical management.
Patients who should be considered for influenza diagnostic testing include:
Hospitalized patients with suspected influenza
Patients for whom a diagnosis of influenza will inform decisions regarding clinical care, infection control, or management of close contacts.
Patients who died of an acute illness in which influenza was suspected.
When a decision is made to use antiviral treatment for influenza, treatment should be initiated as soon as possible without waiting for influenza test results. Antiviral treatment is most effective when administered as early as possible in the course of illness. (http://www.cdc.gov/h1n1flu/recommendations.htm)
Clinicians should be aware that the sensitivities of rapid influenza diagnostic tests (RIDTs) and direct immunofluorescence assays (DFAs) are lower than real-time reverse transcriptase polymerase chain reaction (rRT-PCR) tests and viral culture. A negative RIDT or DFA result does not rule out influenza virus infection. (http://www.cdc.gov/h1n1flu/guidance/rapid_testing.htm). Further, these tests cannot distinguish between 2009 H1N1 and seasonal H1N1 or H3N2 influenza A viruses.
If most circulating influenza viruses have similar antiviral susceptibilities (as is the case currently in the United States), information on the influenza A subtype may not be needed to inform clinical care.
If identification of 2009 H1N1 influenza virus infection is required, testing with a rRT-PCR assay specific for 2009 H1N1 influenza or viral culture should be performed.
Laboratory tests to diagnose 2009 H1N1 influenza, such as rRT-PCR, should be prioritized for hospitalized patients and immunocompromised persons with suspected influenza where RIDT or DFA testing is negative or to determine influenza A virus subtype in patients who have died from suspected or confirmed influenza A virus infection.
Information on testing of pathology specimens for suspected 2009 H1N1 influenza virus infection can be found at (http://cdc.gov/h1n1flu/tissuesubmission.htm).

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CDC H1N1 Flu | Interim Recommendations for Clinical Use of Influenza Diagnostic Tests