Aetiology of community-acquired pneumonia in children treated in hospital

Viral and bacterial antigen and antibody assays were prospectively applied to study the microbial actiology of community-acquired pneumonia in 195 hospitalised children during a surveillance period of 12 months. A viral infection alone was indicated in 37 (19%), a bacterial infection alone in 30 (15%) and a mixed viral-bacterial infection in 32 (16%) patients. Thus, 46% of the 69 patients with viral infection and 52% of the 62 patients with bacterial infection had a mixed viral and bacterial aetiology. Respiratory syncytial virus (RSV) was identified in 52 patients andStreptococcus pneumoniae in 41 patients. The next common agents in order were non-classifiedHaemophilus influenzae (17 cases), adenoviruses (10 cases) andChlamydia species (8 cases). The diagnosis of an RSV infection was based on detecting viral antigen in nasopharyngeal secretions in 79% of the cases. Pneumococcal infections were in most cases identified by antibody assays; in 39% they were indicated by demonstrating pneumococcal antigen in acute phase serum. An alveolar infiltrate was present in 53 (27%) and an interstitial infiltrate in 108 (55%) of the 195 patients. The remaining 34 patients had probable pneumonia. C-reactive protein (CRP), erythrocyte sedimentation rate and total white blood cell count were elevated in 25%, 40% and 36% of the patients, respectively, CRP was more often elevated in patients with bacterial infection alone than in those with viral or mixed viral-bacterial infections. No other correlation was seen between the radiological or laboratory findings and serologically identified viral, bacterial or mixed viralbacterial infections. By using a comprehensive serological panel, the causative agent could be found in over 50% of patients with pneumonia. We conclude that RSV and pneumococcus are the two most common organisms causing pneumonia in children. Our results suggest that mixed viral-bacterial aetiology is common in lower respiratory tract infections affecting children.