A novel method for rapid detection of Streptococcus pneumoniae antigen in sputum and its application in adult respiratory tract infections

A highly sensitive immunochromatography test kit, ODK0501, was developed using specific polyclonal antibodies against the C-polysaccharide moiety of Streptococcus pneumoniae for the rapid detection of S. pneumoniae antigen in sputum samples. The clinical utility of ODK0501 for this detection was evaluated prospectively in 52 adult patients with respiratory infections and compared with that of a urinary antigen detection kit. Overall, 21 patients (40.4 %) showed positive results with ODK0501, compared with 16 patients (30.8 %) using the urinary antigen detection kit, and S. pneumoniae was cultured from 18 patients. ODK0501 and the urinary antigen detection kit exhibited a sensitivity of 94.4 and 55.6 % (P<0.01), respectively, and a specificity of 88.2 and 82.4 %, respectively. Eleven of thirteen patients with conflicting results between the two test kits exhibited consistent results for sputum cultures. Moreover, eight out of nine patients positive for ODK0501 and negative for the urinary antigen detection kit were S. pneumoniae culture-positive, including five who exhibited phagocytosis, indicating S. pneumoniae as a causative agent of infection, in Gram staining of sputum samples. These results suggest that the ODK0501 direct sputum detection kit is more clinically useful than the urinary antigen detection kit in adult patients with respiratory infections.