Evaluation of a rapid immunochromatographic ODK0501 assay for detecting Streptococcus pneumoniae antigens in the sputum of pneumonia patients with positive S. pneumoniae urinary antigens

[[[ Background: ]]] A novel, rapid and noninvasive test (ODK0501, RAPIRUN(®)Streptococcus pneumoniae) uses polyclonal antibodies to detect C polysaccharide of S. pneumoniae derived from sputum samples using an immunochromatographic assay. We evaluated its usefulness in Japanese patients with pneumonia who exhibited positive urinary antigen tests for S. pneumoniae (BinaxNOW(®)S. pneumoniae). [[[ Patients and methods: ]]] Forty adult patients with pneumonia treated between May 2011 and August 2013 were enrolled. Bacterial cultures, Gram staining and ODK0501 assays of sputum as well as urinary antigen tests for S. pneumoniae using urine samples obtained from the same patients were performed upon admission, the fourth day after starting antimicrobial treatment and at the end of the antimicrobial treatment. [[[ Results: ]]] Twenty-seven of the 40 patients were positive for ODK0501, while a negative result for ODK0501 was associated with low-quality sputum samples according to the Geckler classification of sputum. The sensitivity and specificity of the ODK0501 assay in the 40 patients were 90.9% and 61.1%, respectively, based on the culture results. The results obtained with this kit were more favorable than those observed on Gram staining. The ODK0501 assay also showed a rapid reaction to the disappearance of S. pneumoniae in the sputum samples, while approximately 80% of the patients exhibited persistent positive results on the urinary antigen detection tests at the end of treatment. [[[ Conclusions: ]]] The ODK0501 test is a noninvasive, rapid and accurate tool for diagnosing respiratory infections caused by S. pneumoniae, although good quality sputum must be obtained prior to adequate treatment with antibiotics.