ICU Sinks Act as Persistent Reservoirs Exchanging Resistant Bacteria with Patients in Dutch Study

Intensive care unit sinks appear to function as a persistent reservoir in the exchange of multidrug resistant Enterobacteriaceae with patients, according to a longitudinal study conducted at the intensive care wards of two Dutch hospitals. The research, published in Antimicrobial Resistance & Infection Control, examined patient-environment transmission dynamics in a non-outbreak setting, combining retrospective patient data with prospective environmental sampling over an extended period.

The study team sampled sink drains, faucet aerators, high-touch sites of medical devices, and beds in both patient rooms and non-patient rooms across the two ICUs. Environmental sampling was repeated up to ten times per site over the course of 18 months, spanning 2022 to 2023. Alongside this prospective sampling, the researchers collected patient isolates and epidemiological data retrospectively from 2017 to 2022, and prospectively during the environmental sampling period itself.

Isolates were classified as multidrug resistant Enterobacteriaceae (MDRE) if they showed resistance to third-generation cephalosporins, gentamicin, ciprofloxacin and cotrimoxazole, and tested positive by PCR for the antimicrobial resistance genes blaCTX-M-15, qnrB1 and blaOXA-1-aac(6′)-Ib-cr. This shared resistance phenotype and genotype allowed the researchers to compare isolates from patients and the environment on a common genetic basis.

The environmental sampling yielded 553 MDRE isolates from 990 samples, with the overwhelming majority, 97.1 percent, recovered from sink drains rather than from other sampled sites. In parallel, 136 isolates were obtained from 91 patients. Both environmental isolates and patient isolates were concentrated at a single ICU: 98.7 percent of environmental isolates and 91.2 percent of patient isolates, corresponding to 80 patients, came from one of the two wards.

To assess whether patient and environmental isolates were related, the researchers whole genome sequenced patient isolates and a subset of environmental isolates using Illumina technology. Clonal clusters were identified using single nucleotide polymorphism analysis with a threshold of 25 or fewer SNPs, and candidate clusters were then evaluated for spatial and temporal epidemiological links between patients and environmental sites.

This combined genomic and epidemiological assessment identified a total of 19 patient-environment SNP-clusters, incorporating 75 environmental and 36 patient isolates drawn from eight distinct Enterobacteriaceae species. The clusters therefore spanned multiple species and clones rather than a single outbreak strain, a pattern the authors describe as highly diffuse.

Epidemiological investigation showed spatial links with environmental isolates for 31 patients. Temporal links, which take the order of detection into account, indicated possible transmission events from sink to patient for seven patients, and from patient to environment for three patients. These findings suggest that transmission in this setting moved in both directions between sinks and patients, without a single dominant route or strain.

The authors conclude that ICU sinks form an inherent and persistent risk factor in the exchange of MDRE with patients. They suggest that patient colonization rates could likely be reduced by reconsidering the role and necessity of sinks in the ICU environment, combined with prospective genomic monitoring of patient and remaining sink drain MDRE isolates to detect patient-environment clusters and facilitate targeted interventions.

As the authors note, the study was conducted in a non-outbreak setting, meaning the findings reflect background transmission dynamics rather than the dynamics of a defined outbreak investigation. The work was carried out at the intensive care wards of two hospitals in the Netherlands, and the analysis combined retrospective and prospective elements, with environmental sampling conducted between 2022 and 2023 and patient data extending back to 2017.

Subject of Research: Patient-environment transmission dynamics of multidrug resistant Enterobacteriaceae between ICU sinks and patients in Dutch hospitals

Article Title: Patient-environment transmission dynamics of multidrug resistant Enterobacteriaceae in a Dutch intensive care unit: a longitudinal retrospective and prospective analysis in a non-outbreak setting

Article References: Rossel, C. A. J., Heddema, E. R., Koeck, R. M., van der Horst, R. P. J., Janssen, A. H. J. W., Savelkoul, P. H. M., & van Alphen, L. B. (2026). Patient-environment transmission dynamics of multidrug resistant Enterobacteriaceae in a Dutch intensive care unit: a longitudinal retrospective and prospective analysis in a non-outbreak setting. Antimicrobial Resistance & Infection Control. https://doi.org/10.1186/s13756-026-01832-6

Image Credits: AI Generated

DOI: 10.1186/s13756-026-01832-6

Keywords: multidrug resistant Enterobacteriaceae, intensive care unit, sink drains, whole genome sequencing, SNP analysis, nosocomial transmission, antimicrobial resistance, environmental reservoirs, genomic surveillance, infection control, Netherlands, non-outbreak setting