Evaluation of the Sofia Influenza A + B fluorescent immunoassay for the rapid diagnosis of influenza A and B.

Rapid influenza diagnostic tests (RIDTs) can facilitate the appropriate prescription of antivirals for influenza, obviate the need for unnecessary testing and antibacterial agents and allow the implementation of infection control measures. However, the reported sensitivities and specificities of different RIDTs vary widely in clinical settings, as does assay ability to distinguish between influenza types and subtypes. To evaluate the performance of the Sofia Influenza A + B fluorescent immunoassay (FIA) for the detection of influenza A and B during the 2013 Southern Hemisphere influenza season, a total of 209 consecutive respiratory tract swabs from adult patients with an influenza-like illness were tested by both Sofia Influenza A + B and an in-house real-time, reverse transcription-polymerase chain reaction (RT-PCR) assay. Compared to RT-PCR, the sensitivity and specificity of the Sofia Influenza A + B FIA for detection of influenza A was 72.4% and 98.3%, respectively. Too few influenza B positive samples were available during the study to accurately assess the Sofia's performance for influenza B detection. The sensitivity of Sofia Influenza A + B FIA for both influenza A and B detection correlated with the amount of influenza RNA present in the sample as indicated indirectly by the RT-PCR cycle threshold (Ct ). In conclusion, the Sofia Influenza A + B FIA continues to perform well as a RIDT with the circulating influenza strains of the 2013 Southern Hemisphere influenza season.