Hospital-Based Surveillance and Resistance Index Analysis of Antimicrobial Resistance Trends: A Three-Year Study from a Tertiary Hospital in Iran (2021–2023)

Background: Antimicrobial resistance (AMR) poses an escalating global health crisis, yet institution-level temporal analyses that integrate both resistance trends and composite indices remain scarce. Methods: We performed a three-year retrospective analysis (2021– 2023) of all culture-positive bacterial isolates from a tertiary referral hospital in Iran. Antimicrobial susceptibility testing (AST) followed CLSI M02/M07/M100 standards. Annual resistance rates (%R) were calculated for six priority pathogens, and linear regression was used to model temporal changes (slopes, p-values). A composite Resistance Index (RI) was derived to capture cumulative resistance pressure. Results: Among 38,514 specimens, 3109 (8.1%) yielded bacterial growth. E. coli declined significantly (45.0%→ 29.7%, p=0.02), while A. baumannii increased (17.6%→ 26.8%, p=0.03). Regression analysis revealed pronounced upward resistance slopes in A. baumannii (eg, amikacin +8.6%/year, p< 0.001; ciprofloxacin +8.0%/year, p< 0.001) and K. pneumoniae to nalidixic acid (+17.6%/year, p< 0.001). In contrast, significant declines were observed in S. aureus (trimethoprim–sulfamethoxazole − 27.8%/year, p< 0.001), Enterobacter spp. (ampicillin − 42.5%/year, p< 0.001), and carbapenem resistance in K. pneumoniae and P. aeruginosa . The RI highlighted persistently extreme resistance in A. baumannii (> 90%) and high levels in P. aeruginosa (> 70%), with moderate but variable indices in E. coli and K. pneumoniae (50– 70%). Conclusion: This single-center study demonstrates shifting AMR epidemiology with A. baumannii emerging as the dominant multidrug-resistant threat, sustained high resistance in P. aeruginosa , and encouraging declines in certain resistance patterns among E. coli, K. pneumoniae , and S. aureus . By integrating slope-based trends with a composite RI, we provide a scalable framework to convert routine antibiogram data into actionable antimicrobial stewardship programs (ASPs) and infection prevention strategies.