Enzyme immunoassay for the detection of pneumococcal C polysaccharide in sputum of patients with presumptive pneumococcal pneumonia

Abstract

A need exists for more sensitive and specific laboratory methods for the rapid detection of antigens of Streptococcus pneumoniae in body fluids of patients with invasive pneumococcal disease. We evaluated a prototype enzyme immunoassay (EIA) for the detection of pneumococcal C polysaccharide (PnC) in the sputum of patients with presumptive pneumococcal pneumonia. Patients with radiographically confirmed pneumonia had sputum samples collected within a 24-h period of the radiograph. PnC was detected in the sputum samples by EIA. The presence of antigen in sputum was compared to the isolation of pneumococci from sputum by the hospital laboratory. From 35 patients with pneumonia, samples from 12 patients who were culture positive for S. pneumoniae, were all positive by EIA (sensitivity, 100%). Eighteen samples from 23 patients that were culture-negative, were negative by EIA (specificity, 78·2%). Of the five samples that were culture-negative, but EIA-positive, two had documented antibiotic therapy before sputum collection. Sputum samples from patients with pneunonia that grew S. pneumoniae had higher optical density values than samples from patients without pneumonia. These results suggest that the PnC EIA may distinguish between sputa from patients with presumptive pneumococcal pneumonia and those who are carriers of pneumococci.