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

Study objectives: Evaluation of a newly available rapid (15 min) immunochromatographic 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 nonbacteremic pneumonia due to S pneumoniae diagnosed by blood culture and pneumococcal polysaccharide capsular antigen detection by counterimmunoelectrophoresis 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 - 20°C until used. The ICT test was performed following the instructions of the manufacturer. Measurements and results: S pneumoniae antigen was detected in 41 of 51 patients with pneumococcal pneumonia (80.4%); results were positive in 23 of 28 bacteremic eases (82.1%) and in 18 of 23 nonbacteremic cases (78.3%). From 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 pneumococcal pneumonia, especially for the nonbacteremic cases.