Fluorescence-based index from the Sofia Streptococcus pneumoniae fluorescent immunoassay: a prognostic tool for...

Urinary antigen tests, such as the Sofia Streptococcus pneumoniae fluorescent immunoassay, provide rapid and specific detection of S. pneumoniae in community-acquired pneumonia. Although the assay is qualitative, it generates a semi-quantitative fluorescence-based index whose prognostic utility remains underexplored. This study evaluates the relationship between the Sofia S. pneumoniae index and clinical severity in pneumococcal community-acquired pneumonia (CAP). A cross-sectional study of 161 adults with pneumococcal CAP was conducted at a tertiary hospital. Patients with severe pneumonia (quick sequential organ failure assessment (qSOFA) ≥ 2: 10.5 vs 2.3 relative light unit (RLU); CURB-65 ≥ 3: 12.3 vs 2.3 RLU), ICU admission (12.1 vs 2.7 RLU), and 30-day mortality (14.0 vs 3.3 RLU) showed significantly higher median index values (P < 0.001). Area under the curves from receiver operating characteristic curve analysis were 0.75 for qSOFA ≥ 2, 0.79 for CURB-65 ≥ 3, 0.71 for ICU admission, and 0.79 for 30-day mortality. Thresholds identified for CURB-65 ≥ 3 prediction were 6.5 RLU (sensitivity: 79.2%; specificity: 75.9%), 4.2 RLU for qSOFA ≥ 2 (sensitivity: 80.4%; specificity: 64.0%), 12.1 RLU for ICU admission (sensitivity: 51.5%; specificity: 81.9%), and 12.7 RLU for 30-day mortality (sensitivity: 78.6%; specificity: 81.5%). A 10-point increase in the index was associated with higher odds of severe pneumonia (CURB-65 odds ratio [OR]: 1.95; qSOFA OR: 1.48), ICU admission (OR: 1.35), and 30-day mortality (OR: 1.42). The Sofia S. pneumoniae fluorescent index demonstrates significant prognostic value in pneumococcal CAP. It complements traditional severity scores, offering rapid, microbiologically precise insights for guiding management and identifying high-risk patients.IMPORTANCECommunity-acquired pneumonia caused by Streptococcus pneumoniae remains a leading cause of severe illness and death worldwide. Rapid and reliable tools for predicting disease severity are critical to improving patient outcomes. This study evaluates the Sofia S. pneumoniae fluorescent immunoassay, a novel urinary antigen test that provides a semi-quantitative fluorescence index associated with severity/outcomes. By linking a fluorescence-based index to clinical outcomes such as ICU admission and mortality, this research demonstrates the potential of graded microbiological signals to complement traditional scoring systems. These findings highlight a valuable step toward integrating microbiological data into clinical decision-making, ultimately enhancing patient care.