Superior Performance of Nucleic Acid Amplification Tests for Influenza

Rapid diagnostic tests for influenza (RIDT) have been used for decades to diagnose and manage patients who present with signs and symptoms compatible with influenza. They also are useful for helping to determine whether outbreaks of respiratory disease, such as in nursing homes and other settings, might be due to influenza.

The reliability of rapid diagnostic tests depends largely on the conditions under which they are used. Sensitivities of RIDT are approximately 50-70%, and specificities are 90-95%, when compared with viral culture or reverse transcription polymerase chain reaction (RT-PCR). False-positive (and true-negative) results are more likely to occur when disease prevalence in the community is low, which is generally at the beginning and end of the influenza season. False-negative (and true-positive) results are more likely to occur when disease prevalence is high in the community, which is typically at the height of the influenza season.

More recently, two rapid nucleic acid amplification tests (NAATs) for influenza have been approved for diagnostic use; the Alere i Influenza A & B and the Cobas Liat Influenza A/B assay from Roche Diagnostics. Both of these tests are suited for point of care testing because they have CLIA waived status, fast turnaround times, and sensitivities approaching traditional RT-PCR assays.

A recently published systematic review and meta-analysis compared the diagnostic accuracy of these new NAAT tests with traditional rapid tests and conventional RT-PCR. The authors reviewed 162 studies including130 traditional RIDTs, 19 digitally read immunochromatographic immunoassays (DIAs), and 13 NAATs. Most studies included a mixed population of children and adults. The pooled sensitivity for influenza A was 54.4% for RIDTs, 80.0% for DIAs, and 91.6% for NAATs. Sensitivity for influenza B was 53.2% for RIDTs, 76.8% for DIAs, and 95.4% for NAATs. Specificity was consistently high, exceeding 98% for all assays. Digital immunoassays had 25.5% and 23.5% higher sensitivity than traditional RIDTs for diagnosing influenza A and B, respectively. Rapid NAAT sensitivity was superior to that of RIDTs by 37.1% and 41.7% for influenza A and B, respectively, and to that of DIAs by 11.5% and 18.2%. NAATs had similar sensitivity in children and adults.

Most adults with influenza who receive ambulatory care do not receive antiviral therapy, whereas use of antibacterial therapy remains high. A positive test result for influenza increases the likelihood that a physician will prescribe antiviral medication instead of antibiotics. Clinicians want a confirmed diagnosis of influenza before initiating antiviral therapy.  The new NAATs have sufficient sensitivity and specificity to provide actionable results.

References

Ison MG, Contemporary influenza diagnostics: Renewed focus on testing patients. Ann Intern Med. Published online Sep 5, 2017; doi:10.7326/M17-2235.

Merckx J,et al. Diagnostic accuracy of novel and traditional rapid tests for influenza infection compared with reverse transcriptase polymerase chain reaction: A systematic review and meta-analysis. Ann Intern Med. Published online Sep 5, 2017; doi:10.7326/M17-0848

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