Effectiveness of Vancomycin or Beta-Lactam Therapy in Ampicillin-Susceptible Enterococcus spp. Bloodstream Infections

Background: De-escalation to a beta-lactam improves outcomes for patients with a methicillin-susceptible Staphylococcus aureus bloodstream infection (BSI). Whether a similar strategy is appropriate for enterococcal species is less clear. Objective: To determine whether definitive antibiotic selection affects outcomes for patients with an ampicillin-susceptible enterococcal BSI. Methods: This retrospective cohort study included patients over 18 years of age receiving definitive therapy with vancomycin or a beta-lactam for one or more blood cultures positive for Enterococcus spp. isolates between 2007 and 2014. Survival differences were examined using a Kaplan-Meier curve with log-rank test. Results: One-hundred eighty-six patients received definitive therapy with either vancomycin (n = 45, 24.2%) or a beta-lactam (n = 141, 75.8%). The primary outcome, 30-day all-cause mortality, was not different between groups (6.7% vs 7.1%; P = .992). A post hoc analysis of all-cause mortality 1 year after the index BSI was significantly higher in the vancomycin group (51% vs 33%; P = .032). In a Cox proportional hazards regression model, definitive vancomycin was associated with an increased risk of all-cause mortality at 1 year (hazard ratio [HR]: 2.39; 95% confidence interval [CI]: 1.41-4.04). Conclusion: For patients with an ampicillin-susceptible enterococcal BSI, definitive therapy with vancomycin or a beta-lactam was not independently associated with a difference in 30-day all-cause mortality. Whether definitive vancomycin is associated with poor long-term outcomes warrants further exploration.