Abstract
During the 7-year period from September 1978 to August 1985, smear specimens of nasopharyngeal secretions from 3132 patients mainly hospitalized children, taken in different regions in Norway, were examined for respiratory viruses by the rapid immunofluorescence (IF) technique. A positive diagnosis for respiratory syncytial virus (RSV), parainfluenza virus type 1, 2 and 3 or influenza A and B virus was made for 896 patients (29%). The greatest prevalence for all these viruses was observed during the colder months with only sporadic cases during the summer months. A relative increase in parainfluenza virus activity, involving several parainfluenza virus types, was observed in every second autumn and during these periods only sporadic cases of RSV infection were diagnosed. Also both RSV and parainfluenza viruses were less frequently found during influenza virus epidemics and regional differences in RSV activity were observed. During the four autumn periods 1982-85 the monthly number of positive virus identifications by IF followed an epidemic curve, while the corresponding number of negative samples was relatively constant. The results of this study suggest interference between RSV, parainfluenza viruses and influenza virus in reaching their epidemiological peaks. It is suggested that interferon might be a mediator of this effect.