Whether serum
C-reactive protein (CRP) can be used to distinguish bacterial from
viral pneumonia was studied in 193 paediatric patients who were identified in a prospective, population-based study. The proportion of patients < 5 y of age was 51%, 53% of these and 12% of the older patients were treated in hospital. Pneumococcal aetiology of
infection was studied in paired sera by antibody and
immune-complex assays, and chlamydial, mycoplasmal and viral aetiologies by routine antibody assays. CRP concentration was measured by immunoturbidometry.
Pneumococcal infection (
mixed infections with other agents included) was present in 57 cases, mycoplasmal and/or chlamydial
infection (pneumococcal infections excluded) in 43, and
viral infection (pneumococcal, mycoplasmal and chlamydial
infections excluded) in 29 cases. The mean CRP concentrations (95% confidence interval) in these groups were 26.8 mg/l (20.1-33.5 mg/l), 31.8 mg/l (20.5-33.1 mg/l) and 26.1 mg/l (19.1-33.1 mg/l), respectively, and 24.9 mg/l (18.8-31.0 mg/l) in patients with no aetiological findings. When CRP values were compared between the 2 diagnostic groups of
pneumococcal infections (antibody and
immune-complex positive) no difference was found. In infants < 12 months of age the mean CRP concentration was 14.6 mg/l, and in 11 (65%) of them it was unmeasurable (< 10 mg/l). No significant differences were seen between hospitalized patients and outpatients. In conclusion, CRP concentration had no significant association with the microbial aetiology of
pneumonia.