Evaluation of five rapid diagnostic kits for influenza A/B virus

Influenza viruses cause seasonal epidemics associated with high morbidity and mortality. However, even during periods of epidemic prevalence, clinical diagnoses are problematic. Rapid diagnostic tests for the detection of pandemic influenza A/B virus are valuable for their ease of use. Many rapid influenza diagnostic kits were introduced recently in the Republic of Korea (ROK), including Directizen EZ Flu A and B (Becton Dickinson, Sparks, USA), Binax Now Influenza A/B antigen kit (Binax, Portland, USA), Genedia influenza Ag (Green Cross, Yongin, ROK), Humasis Influenza A/B antigen test (Humasis, Anyang, ROK), and SD Bioline rapid influenza kit (Standard Diagnostics, Yongin, ROK). The objective of this study was to evaluate the performance of these five rapid diagnostic kits. The results were compared with those of viral culture and reverse transcription (RT)-PCR. A total of 253 nasopharyngeal swabs were analyzed from 253 patients (influenza A, n=67; B, n=86; negative samples, n=100). The specimens were tested immediately by conventional influenza virus culture and RT-PCR, stored at -80°C, and tested using five rapid test kits. The performance of the five rapid tests kits varied with sensitivities between 71.0 and 82.1% and between 37.2 and 47.7% for detecting influenza A and B, respectively. For influenza A, the sensitivities of the Directizen EZ Flu A and B, Binax Now Influenza A/B antigen kit, Genedia influenza Ag, Humasis Influenza A/B antigen test, and SD Bioline rapid influenza kits were 82.1%, 71.0%, 76.1%, 79.1%, and 82.1%, respectively; those for influenza B were 40.7%, 37.2%, 40.7%, 41.8%, and 47.7%, respectively. The specificity of all rapid tests was 100%. Commercial influenza antigen detection assays are useful tools for the rapid diagnosis of influenza. However, confirmatory testing is always recommended.