A sustained endemic outbreak of vancomycin-resistant Enterococcus faecium: A 30-month surveillance study

Background : The assessment of risk factors for the nosocomial acquisition of colonization and infection by vancomycin-resistant Enterococcus faecium (VREfm) is often problematic due to scarce data on antibiotic use. A 30-month prospective cohort study was conducted to characterize VREfm strains isolated during an outbreak and endemic period, identifying the risk factors, antibiotic consumption, and prevalence of virulence determinants. Methods: The study was conducted in a tertiary care hospital. A representative number (171 patients) of isolates that were classified as resistant to high-level vancomycin (minimum inhibitory concentration (MIC) >= 256 mu g/ml) were investigated. Results: Among 171 colonized patients, 22 (12.9%) developed VRE infection. All VREfm isolates harboured van A genes. Genes codifying virulence factors such as enterococcal surface protein (esp), aggregation substance 1 (asa1), and gelatinase (gel E) were detected in the VREfm studied. All patients infected with VRE had previously been colonized and became infected on average 14 days after colonization. Only previous use of aminoglycosides was a risk factor independently associated with VRE infection; however, glycopeptide consumption in defined daily doses (DDD) per 1000 patient-days was associated with the presence of this microorganism. The monthly colonization pressure ranged from 0.004% to 1.32% during the 30-month study period. Conclusions: We found a high incidence of VRE in a tertiary care hospital, independently associated with the prior use of aminoglycosides and the administration of glycopeptides.