Comparison of two nested PCR, cell culture, and antigen detection for the diagnosis of upper respiratory tract infections due to influenza viruses

Influenza surveillance requires sensitive and rapid diagnostic methods. Different diagnostic procedures have been evaluated on a selected set of nasal swabs sample collected from patients presenting with acute respiratory infection. One hundred fifty-four samples collected during the peak of the influenza epidemic recorded during winter of 1997-1998 in the south of France were processed for influenza detection using antigen detection (ELISA-immunocapture assay), two different nested RT-PCR assays (targeting M and HA genes), and cell culture. Among 154 samples, 93 (60.4%) were positive for influenza detection. Forty specimens (26%) were positive by ELISA, 77 (50%) by culture, 88 (57.1%) using the multiplex HA-PCR and 76 (49.4%) using the M-PCR. Multiplex HA-PCR was thus the most sensitive test. The PCR assay offers an alternative to culture for influenza detection. Nevertheless, culture is efficient for influenza diagnosis and is the only technique that allows the reference centres to collect viral strains and characterise fully new variants.