Usefulness of Sofia Pneumococcal FIAA® test in comparison with BinaxNOWA® Pneumococcal test in urine samples for the diagnosis of pneumococcal pneumonia

The Sofia Pneumococcal FIAA (R) test is a recently introduced immunofluorescent assay automatically read aimed to detect Streptococcus pneumoniae antigen in urine. The aim of this study was to evaluate the usefulness of SofiaFIAA (R) urinary antigen test (UAT) in comparison with classical immunochromatographic BinaxNOWA (R) test for the diagnosis of pneumococcal pneumonia (PP). Observational study was conducted in the Hospital Universitari Vall d'Hebron from December 2015 to August 2016. Consecutive adult patients diagnosed of pneumonia and admitted to the emergency department in whom UAT was requested were prospectively enrolled. Paired pneumococcal UAT was performed (BinaxNOWA (R) and SofiaFIAA (R)) in urine samples. To assess the performance of both tests, patients were categorized into proven PP (isolation of S. pneumoniae in sterile fluid) or probable PP (isolation of S. pneumoniae in respiratory secretion). Sensitivity, specificity, and concordance were calculated. A total of 219 patients with pneumonia were enrolled, of whom 14% had a proven or probable PP, 22% a non-pneumococcal etiology, and 64% an unidentified pathogen. Concordance between tests was good (kappa = 0.81). Sensitivity of SofiaFIAA (R) and BinaxNOWA (R) UAT was 78.6 and 50% for proven PP (p = 0.124), and 74.2 and 58% for proven/probable PP (p = 0.063). Specificity for both tests was 83.3 and 85.5% for proven and proven/probable PP. In patients without an identified pathogen, SofiaFIAA (R) test was positive in 33 (23.6%) cases and BinaxNOWA (R) in 25 (17.8%), so Sofia Pneumococcal FIAA (R) detected 32.6% more cases than BinaxNOWA (R) (p = 0.001). Sofia Pneumococcal FIAA (R) test showed an improved sensitivity over visual reading of BinaxNOWA (R) test without a noticeable loss of specificity.