Pneumonia Etiology and Risk Factors in a Tertiary Hospital During the COVID-19 Era: A Retrospective Analysis (2020–2024)

Rationale Pneumonia remains a leading cause of morbidity and mortality worldwide. The COVID-19 pandemic has significantly altered the epidemiological landscape of respiratory infections. Understanding current etiological patterns and risk factors is crucial for optimal patient management. Objectives To characterize the etiological spectrum of pneumonia and identify clinical and laboratory factors associated with both in-hospital and post-discharge mortality in a large cohort of patients treated during the COVID-19 era. Methods We conducted a retrospective analysis of 1,848 adult patients hospitalized with pneumonia at a tertiary care hospital in Linz, Austria, between January 2020 and January 2024. Data included demographics, comorbidities, laboratory findings, microbiological results, and mortality outcomes. Statistical analyses included univariate correlations and Cox regression models for survival analysis. Measurements and Main Results Etiological agents were identified in only 26.4% of cases, with SARS-CoV-2 being the most frequently detected pathogen (8.7%). In-hospital mortality was 15.1%. Significant risk factors for in-hospital mortality included chronic kidney disease ( φ = 0.057, p = 0.015), dysphagia ( φ = 0.061, p = 0.009), malignancy ( φ = 0.086, p < 0.001), and detection of specific pathogens including Candida albicans, Staphylococcus aureus, and Enterobacter cloacae. Higher HDL levels ( r = -0.120, p < 0.001) and longer hospital stays were associated with improved survival. Post-discharge mortality risk factors included advanced age, elevated CRP levels, and multiple comorbidities, while obesity demonstrated a paradoxical protective effect (HR = 0.628, p = 0.015). Conclusions This study reveals a high rate of unidentified pathogens and identifies specific clinical and microbiological factors associated with pneumonia outcomes during the COVID-19 era. The obesity paradox and protective effect of HDL cholesterol warrant further investigation.