Pathogen identification and outcome in adult patients with community-acquired pneumonia in Switzerland: findings from the Swiss CAPNETZ cohort study

Abstract Background Community-acquired pneumonia (CAP) causes significant morbidity and mortality, but Swiss data are limited. We analyzed the Swiss CAPNETZ cohort to describe patient characteristics, pathogens, diagnostics, and outcomes. Methods Adults with CAP were prospectively enrolled between 2010 and 2022 at two tertiary hospitals. Data on demographics, comorbidities, microbiology, and outcomes were collected. Mortality was assessed at 28 and 180 days. Results Among 478 patients, 97.7% were hospitalized (median 7 days), and 76.4% had ≥ 1 comorbidity. ICU admission occurred in 7.3%. Overall mortality was 2.9% at 28 days and 5.5% at 180 days, increasing during the COVID-19 pandemic (28-day: 5.7%; 180-day: 10.9%). Higher mortality was observed in older, immunosuppressed, and oncologic patients. The etiological pathogens were detected in 38.3%, and molecular testing of sputum and bronchioalveolar lavage (BAL) enhances pathogen detection rates. Bacterial monoinfections predominated (20.2%), followed by viral (7.4%) and mixed infections (9.5%). Leading pathogens were Streptococcus pneumoniae (35.0%) and Haemophilus influenzae (16.1%). In immunocompromised patients, H. influenzae predominated. Conclusion Overall mortality of CAP stays high. S. pneumoniae remains the most common pathogen overall, while H. influenzae is the most frequent pathogen in immunocompromised patients. Molecular testing of sputum and BAL improves pathogen detection.