Influenza rapid diagnostic test background and treatment

The Rapid Influenza Diagnostic Test (RIDT) uses the detection of influenza virus nucleoprotein antigens to determine whether a person is currently infected with influenza.Commercially available RIDTs provide results within 30 minutes.These results can be observed by color changes or other visual signals.For clinicians,RIDT serves as a first-line test that can be confirmed (especially if negative) by traditional diagnostic tests.RIDT also allows clinicians to rapidly initiate antiviral therapy in high-risk populations,institute effective infection control measures,and make informed decisions about diagnostic investigations. RIDTs have been shown to reduce chest radiographs and blood tests in ambulatory care settings,but do not reduce antibiotic prescriptions or emergency room time.According to one study, the sensitivity of the H1N1 rapid test was 66%, which corresponds to a false negative probability of detecting H1N1 of 34%.

Sample Collection 

The accuracy of RIDT may depend on the collection technique used to obtain the sample.Specimens for RIDT include respiratory specimens,such as throat, nose,and nasopharyngeal secretions,and aspirates or washes collected from the trachea.Interim guidance for detection of novel influenza A viruses using rapid influenza diagnostic tests.This guidance has been revised to clarify that rRT-PCR,developed by the CDC for the detection of novel influenza A (H1N1),is currently authorized by the FDA.FDA authorization,also known as emergency use authorization.

Background

This interim guidance outlines the sensitivity of rapid influenza diagnostic tests (RIDTs) for detection of the novel influenza A(H1N1) virus to help guide the reporting and interpretation of test results.This information does not discuss direct (DFA) or indirect immunofluorescence assays (IFA).This guideline is primarily applicable to clinical laboratories and clinical practices performing influenza testing on respiratory specimens from patients with suspected novel influenza A (H1N1) virus infection.Provides information on laboratory biosafety and interim guidance on clinical testing recommendations.

Flu Diagnostic Tests

A number of different laboratory diagnostic tests are available to detect the presence of influenza virus in respiratory specimens,including direct antigen detection tests,virus isolation in cell culture,or detection of influenza-specific RNA by real-time reverse transcription polymerase chain reaction (rRT-PCR). These tests vary in their sensitivity and specificity for detecting influenza virus,as well as their commercial availability,the time required from specimen collection to results,and the ability of the test to distinguish between different influenza virus types (A vs. B) and influenza A virus subtypes (such as novel H1N1 vs.seasonal H1N1 vs.seasonal H3N2 viruses).Serological testing of acute (within 1 week of onset) and convalescent (collected after 2–3 weeks) sera is useful for establishing retrospective diagnosis of influenza virus infection for epidemiology.However,such serial serological testing is not routinely available in clinical laboratories.Currently,only two FDA-authorized tests are available for confirmation of novel H1N1 influenza virus infection,including the CDC rRT-PCR Swine Flu Panel test;however,other rRT-PCR tests not FDA-approved (such as laboratory-developed tests ) may be able to detect the novel influenza A (H1N1) virus public health labs able to perform CDC rRT-PCR swine flu panel testing.For surveillance purposes and special circumstances,for example, confirmation of novel influenza A(H1N1) virus infection may be required.Seriously ill patients,immunocompromised patients,and pregnant and lactating women. State and local jurisdictions mandate specific influenza test results required for influenza surveillance.

Treatment of confirmed or suspected influenza (who treats)

Prompt empiric treatment is recommended for patients with suspected or confirmed influenza and:

• Illness requiring hospitalization

• Progressive,serious or complicated illness,regardless of previous health conditions,and/or

• Patients at risk for severe illness (see High-Risk Groups below)

How to treat

• Antiviral drugs:oseltamivir (oral),zanamivir (inhaled)

• Start treatment as soon as possible after symptoms appear

• Empiric treatment pending reporting of diagnostic test results

• When definitive diagnosis is required,order definitive diagnostic tests (rRT-PCR*,viral culture) rather than rapid tests (RIDT*, DFA*)* rRT-PCR:real-time reverse transcriptase polymerase chain reaction;RIDT:rapid influenza diagnostic test,DFA:direct immunofluorescence assay.