Quantitative RT-PCR evaluation of a rapid influenza antigen test for efficient diagnosis of influenza virus infection

•The sensitivity of RIDT is low, which affects diagnosis.•A small quantum of influenza virus undetected by RIDT was quantified with qRT-PCR.•Viral suspension left after RIDT was used for nucleic acid amplification testing. Influenza virus infection is diagnosed in most cases using a rapid influenza antigen diagnostic test (RIDT). However, false-negative results are a major concern. By contrast, the nucleic acid amplification test offers high sensitivity and therefore can aid the interpretation of negative RIDT results. In this study, influenza viral loads were quantified with quantitative reverse transcription-polymerase chain reaction (qRT-PCR) using viral suspensions left over after RIDT, and the performance of both methods was evaluated. qRT-PCR detected as few as 103copies/mL of influenza viruses A and B, whereas RIDT showed negative results for viral loads less than 107 and 105copies/mL of influenza viruses A and B, respectively. These results indicate that small quantities of the virus that cause false-negative RIDT results can be detected efficiently with qRT-PCR follow-up. In addition, influenza A virus subtype was determined using qRT-PCR.