Prevalence of vancomycin-resistant Enterococcus spp. and associated resistance patterns among isolates collected over a decade of SENTRY Program surveillance in North America

Abstract number: P690

Castanheira M., Biedenbach D., Sader H., Fritsche T., Jones R.

Objective: To investigate the susceptibility pattern of E. faecalis and E. faecium in the USA and Canada medical centres over 10 years; secondarily, to analyse trends in vancomycin-resistant Enterococcus spp. (VRE) in North America during the same period.

Methods: Isolates from bloodstream infection (BSI; 7,284) and other sources (2,763; mainly urine and wound) recovered as part of a 10-year surveillance programme (1997–2006) were analysed for susceptibility profiles. Isolates were collected from medical centres in the USA (52) and in Canada (8) and were tested at a central laboratory (JMI Laboratories, North Liberty, IA) using CLSI broth microdilution methods and interpretation criteria.

Results: Overall, the VRE rate was higher in BSI (19.1%) compared to other sources (14.5%). In the USA, VR E. faecalis rates were stable over ten years (3.3%) with significant year-to-year variation but without trending. In contrast, VR E. faecium steadily increased from 50 to 70%. The percentage of vanA phenotype increased in both species over the years, becoming the predominant resistance phenotype in more than 85% of VRE isolates. The table shows the yearly progression of VRE BSI isolates in the USA and van phenotypes. In Canada, VRE was documented in <1% of BSI isolates and included E. faecium only. Higher resistance rates to other agents were noted among VRE compared to susceptible strains. These included ampicillin-resistant E. faecalis at 13%, ciprofloxacin-resistance at 95% for both species and high-level gentamicin and streptomycin resistance rates were 20–40% higher among VRE compared to vancomycin-susceptible strains. Linezolid-resistance was 1.3% and 2.5% among VR E. faecium and E. faecalis, respectively, compared to <0.5% among vancomycin-susceptible isolates.

Conclusions: At the beginning of this study (1997), VRE were considered to be primarily a USA problem. As expected, VRE has disseminated within other countries, becoming a worldwide concern. The spread of VRE in North America warrants continued susceptibility profiling of large numbers of isolates from multiple medical centres to track changes. The 20%E. faecium VR increase in the USA (nearly all caused by the presence of vanA) and an associated increase in co-resistance has been alarming. Other countries should take note of the USA VRE experience and initiate infection control measures to limit this important pathogen from becoming widely endemic.