Impact of vancomycin resistance on attributable mortality among Enterococcus faecium bloodstream infections: propensity score analysis of a large, multicentre retrospective study

Background Conflicting results exist about mortality risk of infections caused by vancomycin-susceptible Enterococcus faecium (VSEfm) and vancomycin-resistant Enterococcus faecium (VREfm). Our aim was to compare risk factors and clinical outcomes among patients with VSEfm and VREfm bloodstream infections (BSIs). Methods A retrospective, multicentre, cohort study enrolled consecutive adult patients with VSEfm and VREfm BSI diagnosis between 2018-2022. Primary outcomes were 30-day-attributable and 30-day-overall mortality. Multivariable analysis propensity-weighted adjusted for timing to active therapy, Pitt Bacteremia Score (PBS) and Charlson Comorbidity Index (CCI) were performed to identify variables independently associated with 30-day mortality. Results Overall, 446 patients were enrolled: 140 (31.4%) VREfm and 306 (68.6%) VSEfm. Comparatively, VREfm patients more frequently received inappropriate antibiotic therapy, had higher sequential organ failure assessment, PBS and BSI relapses. 30-day-attributable and 30-day-overall mortality did not differ significantly between the two groups. Independent risk factors for 30-day attributable mortality were age (HR 1.04, CI95%, 1.00-1.08, P = 0.022), corticosteroid therapy (HR 3.05, CI95%, 1.24-7.47, P = 0.014) and septic shock (HR 9.10, CI95%, 3.80-21.79, P≤0.001), and overall mortality were age (HR 1.04, CI95%, 1.02-1.05, P≤0.001.), chronic liver failure (HR 1.67, CI95%, 1.02-2.75, P = 0.04) and haematological disease (HR 2.25, CI95%, 1.28-3.94, P = 0.005). Vancomycin resistance is not an independent risk factor for mortality when data are adjusted for confounding factors. Conclusions Adjusted analyses for time to active antibiotic therapy suggest that vancomycin resistance is not an independent risk factor for overall or attributable mortality among patients with Enterococcus faecium BSI. Independent risk factors identified in this study were exclusively comorbidities, severity and corticosteroids use.