Abstract

Background: The coronavirus disease 2019 (COVID-19) pandemic coincided with substantial changes in healthcare delivery and antimicrobial resistance (AMR) patterns worldwide, particularly in intensive care units (ICUs), where invasive procedures and broad-spectrum antibiotics are commonly used. Data from Türkiye remains limited. Methods: This retrospective observational study evaluated bacterial and fungal isolates from adult ICU patients at a tertiary hospital from 2016 to 2025. Microorganisms were identified, and antimicrobial susceptibility testing was performed using standardized methods. Resistance patterns were compared between the pre-pandemic (January 2016–February 2020) and post-pandemic (March 2020–May 2025) periods. Results: A total of 2666 patients and 5433 isolates were analyzed. Gram-negative pathogens showed marked increases in resistance: carbapenem and colistin resistance in Klebsiella pneumoniae were significantly higher in the post-pandemic period (69.6% vs. 44.4% and 60.5% vs. 22.5%, respectively; p < 0.001). Resistance rates to multiple antimicrobial agents also increased in Acinetobacter baumannii and Pseudomonas aeruginosa (p < 0.05). Among Gram-positive bacteria, vancomycin-resistant Enterococcus faecium increased from 10% to 47.1%. Candida auris emerged only in the post-pandemic period, showing high resistance to fluconazole (75%) and amphotericin B (36.7%). Conclusions: Significant differences in AMR patterns were observed between the pre- and post-pandemic periods in this ICU population. Higher resistance rates were observed among several clinically important bacterial pathogens, and Candida auris emerged exclusively during the post-pandemic period. Given the study’s observational design, these findings should be interpreted as temporal associations rather than evidence of a causal effect of the COVID-19 pandemic. Continued antimicrobial stewardship and infection-control measures remain essential to address the growing burden of AMR.

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