Rapid Influenza Diagnostic Tests Evaluated

Recent outbreaks of influenza have underscored the need to validate the accuracy of rapid influenza diagnostic tests (RIDTs) routinely used in clinical settings

The accuracy of seven commercially available tests have been checked as negative results from RIDTs for influenza A (H3N2v) should not be considered reliable evidence of lack of infection.
The US Centers for Disease Control and Prevention (CDC; Atlanta, GA, USA) checked the seven RIDTs using seven different H3N2v viral strains. H3N2v viruses can be detected by qualified public health laboratories using the CDC Flu Real-Time Reverse Transcription Polymerase Chain Reaction (rRT-PCR) Diagnostic Panel for A(H3N2)v (CDC Flu rRT-PCR Dx). Five 10-fold dilutions in physiological saline of each virus grown in Madin-Darby Canine Kidney (MDCK) cells were tested with all of the RIDTs in duplicate.

Tests with BinaxNOW Influenza A&B (Alere; Waltham, MA, USA), Directigen EZ Flu A+B (Becton-Dickinson; Franklin Lakes, NJ, USA), SAS FluAlert A&B (SA Scientific; San Antonio, TX, USA), QuickVue Influenza A+B Test and Sofia Influenza A+B (Quidel; San Diego, CA, USA) were performed according to the procedures in the kit inserts for nasal washes or aspirates. Xpect Flu A&B (Remel; Lenexa, KS, USA) tests were performed according to their procedure for nasal washes and swab specimens transported in liquid media. For the BD Veritor System for Rapid Detection of Flu A+B (Becton Dickinson) test, 100 µL of diluted specimen was added directly to the reagent tube.

Positive and negative controls contained in each RIDT were run before testing the viruses in the study to verify performance of each assay lot, with the exception of FluAlert, which does not provide controls. The CDC reports that only four of the seven RIDTs tested, Directigen, Sofia, Veritor, and Xpect, detected all seven of the H3N2v strains. The BinaxNOW test spotted five of the seven strains, and the QuickVue test found three of the seven. The FluAlert test detected only one of the viral samples in this test.

In this evaluation of seven RIDTs, the ability to detect H3N2v virus varied substantially among the tests. This evaluation emphasizes the fact that a negative RIDT result should not be considered as conclusive evidence of lack of infection with influenza A (H3N2)v. More data are needed on the clinical performance of all RIDTs in detecting H3N2v virus in various respiratory specimens. Results from RIDTs, both positive and negative, always should be interpreted in the broader context of the circulating influenza strains present in the area, level of clinical suspicion, severity of illness, and risk for complications in a patient with suspected infection. The study was published on August 17, 2012, in the journal Morbidity and Mortality Weekly Report (MMWR).

Related Links:
US Centers for Disease Control and Prevention