Clinical Outcomes and Molecular Epidemiology of Vancomycin-Resistant Enterococcus faecium Bloodstream Infection: The Importance of Appropriate Therapy and ST17 Predominance

Background Vancomycin-resistant Enterococcus faecium (VREfm) bloodstream infection (BSI) remains associated with substantial mortality, and timely active therapy may be critical. We evaluated factors associated with 14-day mortality, focusing on anti-VRE therapy, and described contemporaneous molecular epidemiology and biofilm capacity. Methods We randomly selected 150 VREfm blood isolates (50/year) from a tertiary medical center in Northern Taiwan, 2021–2023. Resistance genes were detected by PCR; multilocus sequence typing (MLST) and biofilm assays were performed. The primary outcome was 14-day all-cause mortality, analysed primarily among patients who survived at least three days from BSI onset to mitigate immortal-time bias. Results ST17 predominated (58%), followed by ST78 (20%); all isolates carried vanA. Antimicrobial susceptibility did not differ between ST17 and non-ST17 isolates. ST17 demonstrated greater biofilm formation (median OD 550 0.79 vs 0.44; P <0.001), but neither ST17 status nor biofilm production was associated with 14-day mortality. In the primary outcome analysis (n=137), multivariable analysis showed mortality was independently associated with no anti-VRE therapy (adjusted odds ratio [aOR] 10.44, 95% confidence interval [CI] 1.07-101.86; P =0.04), higher Pitt bacteraemia score (aOR 1.27; P =0.003), autoimmune disease (aOR 21.90; P=0.02), and lower platelet count (aOR 0.92; P =0.003). Compared with no anti-VRE therapy, daptomycin (aOR 0.11, 95% CI 0.01-1.03; P =0.05) and linezolid (aOR 0.05, 95% CI 0.003-0.84; P =0.04) were associated with reduced mortality. Findings were consistent in the 150-patient sensitivity analysis. Conclusions Mortality in VREfm BSI was primarily associated with host factors, illness severity, and receipt of anti-VRE therapy. ST17 predominated and showed enhanced biofilm formation, but was not independently associated with mortality.