Etiological characteristics and infection-related biomarkers in patients with severe community-acquired pneumonia in the emergency department: A retrospective cohort study

Severe community-acquired pneumonia (SCAP) remains a leading cause of infectious disease mortality worldwide. Timely identification of causative pathogens and appropriate antimicrobial therapy are critical determinants of patient outcomes. This retrospective cohort study investigated the etiological features of SCAP and their relationship with infection-related biomarkers, including C-reactive protein (CRP), procalcitonin (PCT), D-dimer (D-D), white blood cell count (WBC), and neutrophil percentage (NEUT), in an emergency department setting. A total of 146 patients with SCAP admitted to Tianjin Medical University General Hospital between March 2018 and March 2019 were included. Pathogen identification was performed through sputum or bronchoalveolar lavage fluid (BALF) cultures. Antimicrobial susceptibility testing was conducted using the Kirby-Bauer disk diffusion method. A total of 154 bacterial strains were isolated from 146 patients. Gram-negative bacteria predominated (145 strains, 94.2%), followed by Gram-positive bacteria (8 strains, 5.2%). The most frequently isolated pathogens were Klebsiella pneumoniae (25.3%), Acinetobacter baumannii (20.1%), and Pseudomonas aeruginosa (13.6%). Extended-spectrum beta-lactamase (ESBL)-producing strains were identified in 17 of 39 K. pneumoniae isolates (43.6%). High-risk clones of K. pneumoniae ST11, ST15, ST307, A. baumannii ST2, P. aeruginosa ST235 were detected in this study. Cefoperazone-sulbactam demonstrated low resistance rates in K. pneumoniae (7.7%), A. baumannii (9.7%), Enterobacter cloacae (8.3%), and P. aeruginosa (14.3%). Abnormal PCT levels were associated with higher proportions of K. pneumoniae and Stenotrophomonas maltophilia infections. Elevated CRP, D-D, WBC, and NEUT levels were more frequently observed in patients infected with K. pneumoniae and A. baumannii. Gram-negative bacteria, particularly K. pneumoniae and A. baumannii, are the predominant pathogens in SCAP. Infection-related biomarkers, especially PCT, show promise in predicting specific etiologies and may guide empirical antimicrobial selection.