Comparative Outcomes of Influenza, SARS-CoV-2, and Respiratory Syncytial Virus Community-Acquired Pneumonia: Insights from an Italian Retrospective Cohort Study

Community-acquired pneumonia (CAP) is a leading cause of morbidity and mortality worldwide. Viral pathogens, particularly influenza, respiratory syncytial virus (RSV), and SARS-CoV-2, are increasingly recognized as key contributors to CAP in hospitalized adults. This single-center, retrospective, cohort study examined and compared the clinical characteristics and outcomes of adults hospitalized with viral CAP due to influenza, SARS-CoV-2, or RSV between January 2022 and December 2023 in Milan, Italy. A total of 165 patients with laboratory-confirmed single-virus infection and clinically and radiologically confirmed pneumonia were included. Patients with SARS-CoV-2 pneumonia presented with the highest in-hospital (20.9%) and 12-month all-cause mortality (51.9%). Influenza patients, although younger, showed increased rates of cardiovascular events and ICU admissions. Bacterial coinfections were most common in influenza cases. Immunocompromised status was the second most frequent comorbidity (37.6%) after arterial hypertension. These findings underscore significant differences in clinical trajectory and long-term outcomes among major viral CAP etiologies and support the need for pathogen-specific management strategies.