The prevalence of faecal carriage of ampicillin-resistant and high-level gentamicin-resistant enterococci among inpatients at 10 major Norwegian hospitals

From March to October 1999, 854 patients hospitalized at 10 major Norwegian hospitals were screened for rectal carriage of ampicillin-resistant enterococci (ARE) and high-level gentamicin-resistant enterococci (HLGRE). A total of 59 ARE carriers (prevalence 6.9%, range 0–22% among hospitals) and 28 HLGRE carriers (prevalence 3.3%, range 1–11%) were detected. All ARE or HLGRE strains were susceptible to vancomycin, whereas 77% of the ARE isolates were resistant to ciprofloxacin. All the ARE strains were identified as Enterococcus faecium, and 48% of these were genomically closely related as shown by PFGE. Specific point mutations in the pbp5 gene were associated with reduced susceptibility to ampicillin. The adjusted risk of becoming a carrier of ARE was related to the use of glycopeptides [odds ratio (OR) = 4.8], the use of any antimicrobial agent (OR = 3.1) and more than one hospital admission during the last six months (OR = 2.0). Twenty-five of 28 HLGRE isolates were Enterococcus faecalis. The aacA/aphD genes were detected in 26 (93%) and the aphA3 in 19 (68%) of the HLGRE isolates. Sixty-four percent of the HLGRE isolates belonged to two PFGE clusters. Consumption of antimicrobial agents was also a significant risk factor for HLGRE colonization (OR = 5.4), while prescription of penicillins was associated with reduced risk (OR = 0.28).