The role of parainfluenza viruses in inspiratory difficulties in children.

Viral findings were prospectively studied in middle and lower respiratory tract infections in 449 hospitalized children during a 12-month follow-up period. A viral aetiology was found in 30 of the 65 children (46%) with inspiratory difficulties. Parainfluenza viruses were the infective agents in 24 of the 30 cases with viral diagnoses (80%), type 2 being the most prominent. There were 38 cases of parainfluenza infections, type 2 being the infective agent in 58% of the 24 cases of parainfluenza infections with inspiratory difficulties but in only 21% of the 14 cases of parainfluenza infections without inspiratory difficulties. Type 2 parainfluenza virus produced inspiratory difficulties in 82% of the cases as opposed to 56 and 50% of the cases for type 1 and 3, respectively. It is concluded that the type 2 parainfluenza virus has a particular association with inspiratory difficulties in children. Viral diagnosis was reached using direct antigen detection in nasopharyngeal specimens by radioimmunoassay in 59% and using complement fixation serology in 76% of parainfluenza infections. Direct antigen detection was especially useful in infants. We suggest that direct antigen detection should be used as a primary virological diagnostic method in small children with middle and lower respiratory tract infections.