Objectives
To evaluate whether vancomycin-resistant Enterococcus faecium (VRE) blood culture isolates reflect the broader hospital VRE epidemiology and to investigate the population structure of VRE in the context of rising bloodstream infection (BSI) rates at our institution.
Methods
Whole genome sequencing (WGS) of VRE BSI isolates and all VRE first annual patient isolates (screening and clinical specimens) at a university tertiary care hospital from 2018 to 2021 was performed. Isolates were analysed using multi-locus sequence typing (MLST), core-genome (cg) MLST, and cluster analysis based on pairwise allelic differences.
Results
From 2018 to 2021, 128 patients had VRE BSI and 218 had VSE (vancomycin-susceptible Enterococcus faecium) BSI, however, VRE became dominant in 2021 (2018: 53 vs. 21; 2021: 42 vs. 48). Concurrently, VRE incidence at our institution rose from 2.7 to 4.3 per 1000 patient days. WGS was performed for 125/128 VRE BSI isolates (97.7%) and 1175/1534 first annual isolates (76.6%). Distribution of complex types (CTs) within VRE blood culture isolates and first annual isolates was generally similar: ST80/CT1065, ST117/CT5130, ST1299/CT1903 and ST117/CT71 were detected most often both in BSI and among first annual isolates (26.5% vs. 26.6%; 14.4% vs. 10.8%; 12.0% vs. 13.5%; 10.4% vs. 13.3%, respectively). Eleven large clusters comprising 10 or more isolates were identified within the representative isolate cohort (a curated dataset including all sequenced blood culture isolates and non-redundant first annual patient isolates), consistent with clonal expansion of successful lineages, likely driven at least in part by in-hospital transmission events, but also possibly by repeated introductions of circulating clones, contributing to the rise in VRE incidence.
Conclusions
Performing WGS on both VRE blood culture and first annual isolates points to several outbreaks as the reason behind the increase in VRE BSI rate. Our results demonstrate that sequencing VRE blood culture isolates alone roughly reflects the distribution of all VRE CTs, making it a pragmatic and resource-efficient approach for obtaining valuable information about the epidemiology of VRE within a hospital.