Long-term epidemiology of bacterial pathogens and antimicrobial resistance in a secondary hospital in China: a 12-year retrospective study

Antimicrobial resistance (AMR) is a growing global health threat. However, long-term epidemiological data from secondary hospitals—a critical component of the healthcare system—remain limited, particularly in China, where national surveillance is largely based on data from tertiary hospitals. Understanding the local epidemiology in these settings is vital for developing effective regional control strategies and guiding empirical antibiotic therapy. We conducted a retrospective analysis of 2,661 clinical bacterial isolates collected from a secondary hospital in Shandong Province, China, between 2014 and 2025. Pathogen distribution was analyzed across patient sex, age groups, specimen types, and temporal trends. Antimicrobial susceptibility data from 2017 to 2025 were used to assess resistance profiles of major pathogens. Key resistant organisms, including methicillin-resistant Staphylococcus aureus (MRSA), extended-spectrum β-lactamase (ESBL)-producing Escherichia coli and Klebsiella pneumoniae , carbapenem-resistant Enterobacterales (CRE), carbapenem-resistant Acinetobacter baumannii (CRAB), and carbapenem-resistant Pseudomonas aeruginosa (CRPA), were further evaluated. Gram-negative bacteria predominated (83.1%), with E. coli (30.9%) and K. pneumoniae (25.6%) as the most common pathogens. Distinct ecological niche patterns were observed: E. coli was overrepresented in urinary and wound samples and in female patients, whereas K. pneumoniae , P. aeruginosa , and A. baumannii were associated with respiratory samples and elderly male patients. Over the 12-year period, the detection rate of K. pneumoniae increased gradually, while that of S. aureus declined. Marked interspecies differences in antimicrobial resistance were evident, with A. baumannii exhibiting high resistance rates (> 60%) to most tested antibiotics, and E. coli showing substantial resistance to commonly used agents, including ampicillin, fluoroquinolones, and gentamicin (> 50%). Among the selected priority resistant pathogens, CRAB showed the highest detection rate (67.1%), while CRE demonstrated a gradual upward trend. ESBL-producing E. coli was the major contributor to AMR burden across most specimen types, particularly in urinary tract infections, whereas ESBL-producing K. pneumoniae and CRAB predominated in respiratory samples, highlighting niche-specific resistance patterns. Our findings reveal ecological and temporal patterns of bacterial distribution and antimicrobial resistance in a secondary hospital setting. By integrating long-term surveillance with stratified analyses across patient populations and specimen types, this study provides context-specific epidemiological evidence that may inform empirical antimicrobial therapy and antimicrobial stewardship, strengthen local AMR surveillance in county-level secondary hospitals, and complement national surveillance programs.