Diagnosing the two main epidemic respiratory viroses: influenza and respiratory syncytial virus infections. Role of molecular virology.

The virologic diagnosis of respiratory syncytial virus (RSV) or influenza v irus infections is useful in cases of severe respiratory diseases in hospit alized children and adults, and in the French influenza survey network. The conventional tools used for virologic diagnosis include direct antigen det ection by immunofluorescence (IFA) or an immunoenzymatic test (ElA), and vi ral isolation technique (VIT). In most cases, IFA and EIA have a slightly l ower sensitivity than WT but, on the other hand, are able to detect at leas t as many IFA- or EIA-positive and WT-negative samples. The results of seve ral teams, using various PCR technologies to search for influenza virus or RSV sequences in respiratory samples, show that the molecular methods detec t more positive cases than the conventional fools. During the influenza epi demic, the detection rate of influenza A virus varies from 57 to 64%, and f rom 38 to 50% for PCR and VIT; respectively. The PCR assays are able to det ect from 57 to 62% of RSV-positive samples, whereas WT and/or IF have an av erage of only 43% for RSV-positive samples. These results underline the lim its of traditional methods. (C) 2000 Editions scientifiques et medicales El sevier SAS.