Bacterial involvement in parainfluenza virus infection in children.

37 children with serologically confirmed parainfluenza virus (PV) infection were studied by new serological methods for evidence of concomitant bacterial infection. 24 of the children were hospitalized because of croup and 13 because of lower respiratory tract infection. Serological evidence of bacterial involvement was found in 4 (11%) of the 37 children, in none of the 24 children with croup but in 31% of the 13 children with PV infection of the lower airways (p less than 0.05). Streptococcus pneumoniae was implicated in 3 cases and Haemophilus influenzae in 1. Serological evidence of staphylococcal involvement was not seen in any case. The 3 patients with pneumococcal involvement had pneumococcal antigen in the acute serum. In all of them pneumonia was associated with PV type 1 or 3, and in 2 serum C-reactive protein was elevated. The data presented support the view, that secondary bacterial infection is rare in children with croup, but common in lower respiratory tract infection caused by PV.