Community-Acquired Pneumonia Outside the Intensive Care Unit: Clinical Characteristics and Impact of Rapid Molecular Diagnostics in the Italian SIS-NET Study

Abstract

Objectives: To describe the clinical, radiological, and microbiological characteristics of community-acquired pneumonia (CAP) managed outside the ICU and evaluate the impact of rapid microbiological diagnostics on hospital outcomes in a multicenter Italian cohort. Methods: In this prospective observational study conducted across seven Italian centers (October 2024-October 2025), 176 adults hospitalized with CAP outside the ICU and a PaO₂/FiO₂ ratio <300 were enrolled. Demographic, clinical, laboratory, radiological, microbiological, therapeutic, and outcome data were collected. Syndromic respiratory panels were performed in a subset of patients. Secondary outcomes included factors associated with in-hospital mortality and time to live discharge within 28 days. Results: Patients were predominantly elderly (mean age 69.7±14.4 years) with high comorbidity burden (Charlson Comorbidity Index 4.9±2.1). Dyspnea, fever, and cough were the most frequent symptoms. Microbiological testing was performed in 48% of cases; viral pathogens were detected more often than bacteria (42.3% vs 27.0%), with viral-bacterial co-detection in 14.1%. In-hospital mortality was 2%, and 3% required ICU transfer. Rapid microbiological testing was independently associated with earlier discharge (HR 1.67, 95%CI 1.17-2.38; p=0.005), while chronic corticosteroid therapy predicted longer hospitalization. Conclusions: CAP outside the ICU mainly affects elderly multimorbid patients. Rapid molecular diagnostics may facilitate earlier discharge by supporting clinical decision-making.