DIAGNOSIS OF RESPIRATORY SYNCYTIAL VIRUS-INFECTIONS

Winter outbreaks of respiratory syncytial virus (RS) infections are the cause of frequent acute lower respiratory diseases in infants. The need to identifiate severe RSV bronchiolitis and to distinguish them from bacterial or other viral pneumonia, and the availability of antiviral therapy have prompted the development of rapid viral diagnostic techniques. Attempts to use IgM antibody in serum as a diagnostic aid have been desapointing. Direct detection of RS antigen in respiratory secretions by the indirect fluorescent antibody test U or ELISA are the procedure of choice. Both methods have advantages over culture of convenience or speed, and can appear of superior sensitivity because of the rapid inactivation of RSV in nasal specimens. Of 1747 nasal aspirates, 1584 (90,6%) were concordant by IF and culture, 111 (6,3%) were IF positive and culture negative, and 52 (2,9%) specimens were IF negative and culture positive. Isolation is also useful to determinate the sensitivity of RS strains to ribavirin. Using a plaque reduction assay, the ID50 and ID90 (mu g/ml) were determinated on 44 RS strains. There was no difference between the ID50 and ID90 values of the RS strains group A or B, and the ID90 mean value : 43,7 mu g/ml was relatively closed to the mean ID50 value : 43,7 mu g/ml. The group A or B of RSV was determinated from infants hospitalized in Caen, France, over 11 consecutive epidemics from 1982 to 1993. Both groups were present in almost equal numbers, but a predominant group was observed in 1987-88 : group A, and in 1983-84 and 1989-90 : group B. A greater clinical severity was observed with group A strains. The amplification of nucleic acid by RT-PCR can be used, but the technic is complex, time-consuming, and there is no theorical nor practical justification for its use in routine for the diagnosis of RS infections.