Pneumococcal serotype distribution and diagnostic yield of serotype-specific urinary antigen detection in adults with CAP in Switzerland, 2016-2021: a prospective cohort study.

BACKGROUND

Streptococcus pneumoniae remains the leading bacterial cause of community-acquired pneumonia (CAP) and a major source of morbidity and mortality in adults. Pneumococcal conjugate vaccines (PCVs) have substantially reduced invasive pneumococcal disease, but serotype replacement has led to shifts in pneumococcal CAP epidemiology. In addition, the identification of S. pneumoniae remains challenging. This study investigated pneumococcal serotype distribution, vaccine coverage, and the diagnostic yield of a serotype-specific urinary antigen detection assay (ssUAD) among adults with CAP in Switzerland between 2016 and 2021.

METHODS

Adult patients enrolled in the Swiss CAPNETZ cohort with available urine samples were analyzed using the Pfizer 24-serotype ssUAD assay. Results were compared with conventional diagnostic methods, including the pneumococcal urinary antigen test (pUAT) and cultures. Serotype distribution, vaccine coverage (PCV13, PCV15, PCV20 and PCV21), and temporal trends were assessed.

RESULTS

Among 234 CAP patients, S. pneumoniae was identified by conventional diagnostics (pUAT and cultures combined) in 37 (15.8%). The ssUAD was positive in 35 patients (15.0%). Among patients with available results from both conventional diagnostics and ssUAD (n = 161), the addition of ssUAD increased pneumococcal CAP detection from 18.6% to 29.2% (p = 0.036). Among ssUAD-positive patients, the most frequent serotypes detected by ssUAD were 3 (n = 12), 8 (n = 5), and 11A (n = 4). Based on ssUAD-derived serotype distribution, vaccine coverage was 54.3% for PCV13, 60.0% for PCV15, 91.4% for PCV20, and 85.7% for PCV21. During 2020-2021, the proportion of serotypes not covered by PCV13 increased from 10/28 (35.7%) to 6/7 (85.7%) (p = 0.018).

CONCLUSIONS

The addition of ssUAD improved S. pneumoniae detection beyond standard methods. Although based on a small number of cases, the shift toward non-PCV13 serotypes underscores the potential benefit of higher-valency vaccines such as PCV20 and PCV21 for adult pneumococcal disease prevention in Switzerland.