External ventricular drain-associated bacterial meningitis and/or ventriculitis in intensive care unit patients: a 13-year analysis of etiology, outcomes, and antimicrobial resistance

External ventricular drain (EVD)-associated meningitis and/or ventriculitis (MEV) remain serious complications in intensive care units (ICUs), particularly when caused by antimicrobial-resistant pathogens. This study aimed to evaluate the etiology, clinical outcomes, and antimicrobial resistance patterns of EVD-associated bacterial MEV over 13 years. In this retrospective single-center study, adult ICU patients with culture-confirmed EVD-associated bacterial MEV between 2013 and 2025 were included. Demographic, clinical, and microbiological data were analyzed. Antimicrobial resistance patterns, including carbapenem, colistin, ampicillin, and methicillin resistance, as well as extended-spectrum β-lactamase (ESBL) production, were evaluated across pre-pandemic, pandemic, and post-pandemic periods. Among 1,001 adult patients who underwent EVD placement, 138 (13.8%) developed EVD-associated MEV; after excluding 25 patients managed in general wards, 113 patients constituted the final study, corresponding to 15.0% of the 753 EVD patients managed in ICUs. Antimicrobial resistance was observed in 70 (61.9%) patients. Acinetobacter baumannii was the most frequently isolated pathogen, followed by Enterobacterales. High resistance rates were observed, including carbapenem resistance in 80% of A. baumannii and 48% of Enterobacterales isolates. ESBL production among Enterobacterales reached 80%. Higher antimicrobial resistance rates were observed in the later study periods, particularly in the post-pandemic period. In univariate analysis, same-pathogen bacteremia ( p = 0.002) was associated with antimicrobial-resistant microorganisms. In EVD-associated MEV, Gram-negative bacteria, particularly Acinetobacter baumannii and Enterobacterales , were frequently identified, with high rates of antimicrobial resistance. Antimicrobial resistance among Enterobacterales appeared to increase over the study period. In unadjusted analyses, higher mortality was observed among patients with infections caused by resistant microorganisms. These findings highlight the value of continuous local resistance surveillance, optimization of empirical antimicrobial therapy based on institutional susceptibility patterns, and antimicrobial stewardship in the management of EVD-associated MEV. Not applicable.