Comparative study of rapid antigen testing and two nucleic acid amplification tests for influenza virus detection.

Introduction: This study aimed to evaluate rapid antigen detection (RAD) and rapid nucleic acid amplification tests (NAATs) to detect influenza virus (IV).

Methods: The conventional RAD test (Quick Chaser Flu A, B: QC), using silver amplified immunochromatography (Quick Chaser Auto Flu A, B: QCA), as well as two NAATs (Xpert Xpress Flu/RSV: Xpert, cobas Influenza A/B & RSV: cobas) were evaluated using nasopharyngeal swabs from suspected cases of influenza. A reference method was performed using real-time reverse transcription polymerase chain reaction according to the manual of the Japanese National Institute of Infectious Disease (NIID).

Results: From a total of 177 samples, 51 were positive according to the NIID assay. The kappa (κ) coefficient in Xpert and cobas for influenza A virus (IAV)/influenza B virus (IBV) was 1.00, which was the highest among the four detection assays. However, the κ coefficients in QC and QCA for IAV/IBV were 0.71-0.77 and 0.87-0.89, respectively. The sensitivities of the RAD tests were 41.7% in QC and 50.0% in QCA at < 6 h after onset, and 100.0% in both QC and QCA at 24-48 h after onset. The cycle threshold (Ct) values were significantly lower in the group in which all detection assays were positive for IAV.

Conclusions: Xpert and cobas have comparable analytical performances and are highly useful as influenza virus detection assays. QC and QCA could show false negatives frequently in the early stage of infection and when viral load is low.