Detection of C polysaccharide in Streptococcus pneumoniae in the sputa of pneumonia patients by an enzyme-linked immunosorbent assay.

The pneumococcal C polysaccharide (PnC) is species specific and believed to be a cell wall component of all pneumococcal types. A sandwich enzyme-linked immunosorbent assay (ELISA) for detection of PnC in sputa has been developed by using a monoclonal antiphosphorylcholine antibody and a polyclonal rabbit anti-PnC antiserum in the test system. A 1-year study of adult hospitalized patients with community-acquired pneumonia was performed. A total of 147 patients with clinical and radiological evidence for pneumonia were accepted for the study. Of these, 105 patients provided a sputum sample upon admission to the ward. The sputa were cultured semiquantitatively as well as tested for the presence of antigen. Of the sputum samples from patients with Streptococcus pneumoniae, 27 of 33 (accounting for a sensitivity of 82%) were positive in the ELISA test. Of the sputum samples from patients with pneumonia of some other known or suspected etiology, 32 of 34 (accounting for a specificity of 94%) were negative. In addition, 7 sputum samples from 31 patients with pneumonia of unknown etiology were positive. The ELISA test described here is in our opinion a sensitive and specific test for detecting PnC from S. pneumoniae in sputa from patients with untreated pneumonia.