Detection of streptococcus pneumoniae antigen by a rapid immunochromatographic assay in urine samples

Study objectives: Evaluation of a newly available rapid (15 min) immunochro matographic membrane test (ICT) to detect Streptococcus pneumoniae in urine samples, in order to assess its utility in the diagnosis of bacteremic and nonbacteremic pneumococcal pneumonia. Design: Retrospective study. Setting: We studied urine samples from 51 patients with bacteremic and nonb acteremic pneumonia due to S pneumoniae diagnosed by blood culture and pneu mococcal polysaccharide capsular antigen detection by counterimmunoelectrop horesis in urine samples, 16 patients with probable pneumococcal pneumonia, 71 patients with nonpneumococcal pneumonia, and 16 patients with pneumonia but no pathogen identified. Urine samples were collected and frozen at - 2 0 degreesC until used. The ICT test was performed following the instruction s of the manufacturer. Measurements and results: S pneumoniae antigen was detected in 41 of 51 pat ients with pneumococcal pneumonia (80.4%); results were positive in 23 of 2 8 bacteremic cases (82.1%) and in 18 of 23 nonbacteremic cases (78.3%). Fro m patients with a diagnosis of presumptive pneumococcal pneumonia, antigen was detected in seven urine samples (43.7%) and also in one case of the 16 patients with pneumonia but no pathogen identified. The specificity of the ICT test was 97.2%. Conclusion: The ICT assay is a valuable tool for the diagnosis of pneumococ cal pneumonia, especially for the nonbacteremic cases.