Defining the role of the environment in the emergence and persistence of vanA Vancomycin-Resistant Enterococcus (VRE) in an intensive care unit : a molecular epidemiological study

OBJECTIVE: To describe the transmission dynamics of the emergence and persistence of vanA vancomycin-resistant enterococcus (VRE) in an intensive care unit (ICU) using whole-genome sequencing of patient and environmental isolates. DESIGN: Retrospective cohort study. SETTING: ICU in a tertiary referral center. PARTICIPANTS: Patients admitted to the ICU over an 11-month period. METHODS: VanA VRE isolated from patients (n=31) were sequenced using the Illumina MiSeq platform. Environmental samples from bed spaces, equipment, and waste rooms were collected. All vanA VRE-positive environmental samples (n=14) were also sequenced. Data were collected regarding patient ward and bed movements. RESULTS: The 31 patient vanA VRE isolates were from screening (n=19), urine (n=4), bloodstream (n=3), skin/wound (n=3), and intra-abdominal (n=2) sources. The phylogeny from sequencing data confirmed several VRE clusters, with 1 group accounting for 38 of 45 isolates (84%). Within this cluster, cross-transmission was extensive and complex across the ICU. Directionality indicated that colonized patients contaminated environmental sites. Similarly, environmental sources not only led to patient colonization but also to infection. Notably, shared equipment acted as a conduit for transmission between different ICU areas. Infected patients, however, were not linked to further VRE transmission. CONCLUSIONS: Genomic sequencing confirmed a predominantly clonal outbreak of VRE with complex transmission dynamics. The environmental reservoir, particularly from shared equipment, played a key role in ongoing VRE spread. This study provides evidence to support the use of multifaceted strategies, with an emphasis on measures to reduce bacterial burden in the environment, for successful VRE control.