Molecular Tests for Rapid Diagnosis of Influenza
Rapid diagnostic tests for influenza can help in the diagnosis and management of patients who present with signs and symptoms suggestive of influenza. These tests provide results in less than 30 minutes, are often CLIA-waived, and can be used as point of care tests. They also differentiate between types A and B, which is helpful in choosing therapy.
For many years, rapid antigen tests have been used for diagnosis of influenza. The reliability of rapid antigen tests depends largely on the quality of nasopharyngeal swab collected and prevalence of influenza in the community at the time of collection. Sensitivities of rapid influenza tests are low, approximately 50-70%. Specificities are higher, approximately 90-95%, when compared with viral culture or standard reverse transcription polymerase chain reaction (RT-PCR).
False-positive results are most likely early in the influenza season, when prevalence in the community is low. False-negative results are more likely to occur when disease prevalence is high in the community, which is typically at the height of the influenza season. Collecting respiratory specimens within 48 to 72 hours after onset of symptoms, when viral load in the nasopharynx is highest, can minimize false results.
Recently, two rapid molecular tests have received FDA approval for detection of influenza A and B directly from nasopharnygeal swabs. Sensitivity is much higher than rapid influenza tests and is comparable to standard RT-PCR assays. The Alere I assay for influenza A and B was the first CLIA waived test to receive approval. The second assay to achieve FDA clearance was the Cobas Liat influenza A and B test, which uses real-time PCR to generate results in approximately 20 minutes.
Both of these rapid molecular tests give more reliable results than rapid antigen tests. Rapid molecular testing will eventually replace rapid antigen tests for diagnosis of influenza in physician offices and emergency departments.
