Pneumococcal pneumonia diagnosis by demonstration of pneumolysin antibodies in precipitated immune complexes - A study in 350 Philippine children with acute lower respiratory infection

In searching for suitable methods for aetiological diagnosis of pneumococca l disease me determined capsular polysaccharide, C-polysaccharide and pneum olysin antibodies bound in immune complexes (IC) in Filipino children. Sera were obtained from 150 healthy infants (all under 12 months old) and from 350 paediatric patients (mean age 18 months) hospitalized with severe pneum onia. The findings in healthy children were not associated with age, sex or pneumococcal carrier status; 3-7% exceeded the cut-off limits for positivi ty in different antibody assays. By contrast, 97 (51%) of the 190 patients with a complete 3-sample series exceeded the cut-off limit for IC-bound pne umolysin-IgG in at least 1 of the serum samples studied. Positivity rates f or IC-bound pneumolysin-IgG in the admission day, in-patient and convalesce nt sample of the 350 patients were 25%, 25% and 34%. Pneumolysin-IgM, capsu lar polysaccharide and C-polysaccharide antibodies in the IC were positive in only 4-6% of the patients' samples. IC-bound pneumolysin-Ige antibody as say seem to be a useful method for species-specific diagnosis of pneumococc al infections.