Applications of a duplex reverse transcription polymerase chain reaction and direct immunofluorescence assay in comparison with virus isolation for detection of influenza A and B.

A duplex reverse transcription polymerase chain reaction (RT-PCR) and direct immunofluorescence assays (DFAs) were evaluated for detection of influenza types A and B in comparison with virus isolation in Madin-Darbin canine kidney cells. Four hundred four nasal wash were collected from individuals presenting with acute respiratory symptoms during 2001 to 2003 influenza seasons. According to the reference method, 78 (19.3%) samples were infected by influenza virus: 46 were type A and 32 type B. The overall concordance between the 3 assays was 96%, with 317 negative and 71 positive samples in all tests. RT-PCR reached 92.3% sensitivity and 98.5% specificity, and for DFA, the corresponding values were 93.6% and 97.2%, respectively. DFA and RT-PCR could be applied in different routine settings, resulting as an advantage compared with virus isolation: DFA provides rapid results for clinical purposes, but RT-PCR allows running more samples, an important concern in early pandemic circumstances.