Diagnosis of Streptococcus pneumoniae pneumonia by quantitative enzyme linked immunosorbent assay of C-polysaccharide antigen

Aims-To evaluate the use of a quantitative enzyme linked immunosorbent assay (ELISA) detecting C-polysaccharide (PnC) antigen in sputum for the diagnosis of Streptococcus pneumoniae infection. Methods-Specimens of sputum from 60 patients with acute community and hospital acquired pneumonia and infective exacerbations of obstructive airways disease were examined by semiquantitative culture and antigen ELISA. Results-Using a cutoff value of 1 μg/ ml PnC antigen for a positive result, the sensitivity of this assay was 90-3%, specificity 93*1%, predictive value of a positive result was 93-5%, and the predictive value of a negative result 89*6%. Conclusions-Quantitation of C-polysaccharide antigen in sputum by ELISA distinguishes between carriage of oral bacteria which express PnC-like antigen and infection with S pneumoniae and compares favourably with other diagnostic methods.