Trends in the Incidence and Antibiotic Resistance of Enterococcal Bloodstream Isolates: A 7-Year Retrospective Multicenter Epidemiological Study in Italy

The spread of resistance to vancomycin and other last-resort drugs in Enterococcus spp. remains of concern. In Italy, surveillance data for enterococcal bloodstream isolates in humans are scant. The aim of our study was to assess the incidence trends of bacteremias due to Enterococcus species and their prevalence trends of antimicrobial resistance. We retrospectively included all consecutive not-duplicate Enterococcus species isolated from blood cultures, in patients from 11 Italian hospitals (2011-2017). Incidence was defined as the number of isolates per 10,000 patient-days, while resistance prevalence was defined as the number of resistant strains divided by the number of tested strains. We included 4,858 isolates (59%, 36%, and 5% due to Enterococcus faecalis, E. faecium, and other Enterococcus spp., respectively). Over the study period, the incidence of bacteremias due to E. faecalis (incidence rate ratio [IRR]: 1.02, 95% confidence interval [CI]: 1.00-1.04, p = 0.008) and E. faecium increased (IRR: 1.03, 95% CI: 1.01-1.05, p < 0.001) alongside with the whole enterococcal bacteremias trend (IRR: 1.02, 95% CIs: 1.01-1.04, p = 0.002). A progressive increase in vancomycin-resistant E. faecium (VREfm) bacteremias was observed. Resistance to tigecycline and linezolid was rarely reported. The incidence of enterococcal bloodstream isolates is increasing in Italy, together with the prevalence of VREfm. Resistance to linezolid, a cornerstone drug used in the treatment of VRE bloodstream infection, remains negligible.