The research team, led by Esra Zerdali of the University of Health Sciences’ Haseki Training and Research Hospital in İstanbul, together with colleagues from Tekirdağ Namık Kemal University and Haydarpaşa Numune Training and Research Hospital, analyzed data from 1,001 adult patients who underwent EVD placement between 2013 and 2025. Of these, 138 patients, or 13.8 percent, developed EVD-associated meningitis and/or ventriculitis, a complication the researchers abbreviate as MEV. After excluding 25 patients who were managed in general wards rather than intensive care, the final study population comprised 113 patients, corresponding to 15.0 percent of the 753 EVD patients treated in ICUs during the study period. Every case was culture-confirmed, meaning that bacteria were actually grown from cerebrospinal fluid samples rather than diagnosed on clinical suspicion alone.

The microbiological findings are the study’s most striking contribution. Acinetobacter baumannii, a Gram-negative bacterium notorious for its ability to survive on hospital surfaces and acquire resistance genes, emerged as the most frequently isolated pathogen, followed by Enterobacterales, a family of Gram-negative bacteria that includes Escherichia coli and Klebsiella species. This distribution stands in contrast to the classical teaching that staphylococci dominate device-associated infections, and it underscores how the ecology of hospital-acquired brain infections has shifted in settings where multidrug-resistant Gram-negative organisms circulate widely.

Resistance rates among the recovered isolates were alarmingly high. Carbapenem resistance, which renders one of the last-line classes of antibiotics ineffective, was documented in 80 percent of A. baumannii isolates and 48 percent of Enterobacterales isolates. Extended-spectrum beta-lactamase (ESBL) production, an enzymatic mechanism that destroys many penicillins and cephalosporins, was found in 80 percent of the Enterobacterales. Overall, antimicrobial resistance was identified in 70 of the 113 patients, or 61.9 percent. The researchers also evaluated resistance to colistin, ampicillin, and methicillin across the cohort, and they stratified their findings into pre-pandemic, pandemic, and post-pandemic periods to track how the resistance landscape evolved over time.

That temporal analysis revealed a disturbing trend: resistance rates climbed in the later study periods, with the post-pandemic era showing particularly elevated levels of drug-resistant organisms. This pattern echoes observations from many intensive care units worldwide, where the enormous patient surge, prolonged hospitalizations, and intensified broad-spectrum antibiotic use during the COVID-19 pandemic are believed to have accelerated the selection and spread of resistant bacteria. The Turkish data suggest that, at least in this center, the microbiological aftermath of the pandemic has not receded but has instead become entrenched in the ICU environment.

Using univariate statistical analysis, the investigators identified one factor significantly associated with infections caused by antimicrobial-resistant microorganisms: same-pathogen bacteremia, the presence of the identical bacterial species in the bloodstream, was associated with resistant organisms with a p-value of 0.002. This finding has practical implications, because it suggests that when a patient with an EVD develops both meningitis or ventriculitis and a bloodstream infection with the same organism, clinicians should anticipate a higher likelihood that the pathogen is drug-resistant and adjust empirical therapy accordingly while awaiting culture and susceptibility results.

The outcome data add further weight to the study’s conclusions. In unadjusted analyses, mortality was higher among patients whose infections were caused by resistant microorganisms. This association, while not adjusted for confounders such as underlying illness severity, aligns with the broader literature on multidrug-resistant hospital infections, where the scarcity of effective antibiotics delays appropriate treatment and worsens prognosis. Infections of the central nervous system are particularly unforgiving in this regard, because many antibiotics penetrate poorly across the blood-brain barrier, leaving clinicians with a very short list of agents that can reach therapeutic concentrations in the cerebrospinal fluid.

The authors emphasize that their findings highlight the value of continuous local resistance surveillance, the optimization of empirical antimicrobial therapy based on institutional susceptibility patterns, and antimicrobial stewardship programs in the management of EVD-associated MEV. In practical terms, this means that an ICU’s own resistance data, rather than generic guidelines, should drive the choice of initial antibiotics when EVD-associated infection is suspected. It also reinforces the importance of infection prevention measures around EVD insertion and maintenance, since every prevented infection is an infection for which no last-line antibiotic needs to be spent.

The study’s retrospective, single-center design carries inherent limitations that the authors acknowledge through their careful framing of the results. The unadjusted mortality analysis cannot establish that resistance itself caused worse outcomes, and the findings from one hospital in İstanbul may not generalize to centers with different bacterial ecologies. Nevertheless, the 13-year span, the culture-confirmed case definition, and the detailed resistance phenotyping make this one of the more comprehensive longitudinal portraits of EVD-associated central nervous system infection available, and the ethical approval from the Haseki Training and Research Hospital ethics committee, granted in September 2022 under protocol number 171-2022, ensured the work complied with the Declaration of Helsinki.

For clinicians, the message is clear: as Gram-negative bacteria such as A. baumannii and resistant Enterobacterales increasingly dominate the landscape of device-associated brain infections, empirical treatment protocols must be grounded in up-to-date local surveillance, and the rise of resistance in the post-pandemic period demands renewed vigilance. For researchers, the study opens avenues for prospective, multicenter investigations that could adjust for confounders and test whether targeted stewardship interventions can bend the resistance curve. For patients and families, it is a reminder that the battle against antimicrobial resistance is being fought not only in the laboratory but at every bedside where a life-saving tube meets an opportunistic microbe.

Subject of Research: EVD-associated bacterial meningitis and ventriculitis etiology, outcomes, and antimicrobial resistance in ICU patients

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

Article References: External ventricular drain-associated bacterial meningitis and/or ventriculitis in intensive care unit patients: a 13-year analysis of etiology, outcomes, and antimicrobial resistance. (n.d.). https://doi.org/10.1186/s12879-026-14646-z

Image Credits: AI Generated

DOI: 10.1186/s12879-026-14646-z

Keywords: external ventricular drain, meningitis, ventriculitis, antimicrobial resistance, Acinetobacter baumannii, Enterobacterales, carbapenem resistance, ESBL, intensive care unit, cerebrospinal fluid, antimicrobial stewardship, hospital-acquired infection