Comparison of RT-PCR with other diagnostic assays for rapid detection of influenza viruses

To compare the effectiveness of reverse transcription-polymerase chain reaction (RT-PCR), shell vial culture and cytospin assay as laboratory techniques for rapid diagnosis of influenza infections, a retrospective study was carried out on 270 aliquots of oropharyngeal swabs collected from October 1993 to March 1996 and already characterized by standard isolation procedures, and a prospective study in which 65 clinical samples taken from patients with influenza-like syndrome between October 1996 and March 1997 were tested. In the retrospective study, using conventional isolation as the gold standard, the sensitivity of RT-PCR and cytospin assay for virus A was 100% (95% confidence interval (Cl), 89.1-100) and for virus B it was 100% (95% Cl, 56.1-100) compared with 77.5% (95% Cl, 61.1-88.6) and 71.4% (95% Cl, 30.3-94.9) for shell vial culture. The specificity of all the three assays was 100% (95% Cl, 98.0-100) for virus A and 100% (95% Cl, 98.2-100) for virus B. In the prospective study the sensitivity of RT-PCR was greater than that of the other tests considered, both rapid and standard. It is suggested that RTPCR should be employed in combination with conventional culture techniques in routine diagnosis of influenza infections in order to obtain results more rapidly and to improve virus detection even in circumstances in which standard isolation could be problematic.