Vancomycin resistance emerging in a clonal outbreak caused by ampicillin-resistant Enterococcus faecium

Objective To describe the first nosocomial outbreak of ampicillin-resistant Enterococcus faecium (ARE) in Norway, where a few vancomycin-resistant str ains have also been identified. Methods All cases of ARE and vancomycin-resistant Enterococcus faecium (VRE ) diagnosed by the medical microbiological laboratories in a region inhabit ed by approximately 1 million people were registered. Isolates obtained dur ing the period 1 January 1995 to 31 December 1996 were characterized by pul sed field-gel electrophoresis and the clinical data were recorded. Results One hundred and forty-nine patients (64 males, 85 females, mean age 70.5 years) were infected with ARE. Isolates from 115 cases were genomical ly related to the outbreak strain. infections included bacteremia (14), wou nd infections (31), urinary tract infections (97) and other infections (sev en). Most had a severe underlying disease and 93% of the patients had recei ved antibiotics for a mean time of 23 days. Twenty-four patients (16.1%) di ed during hospitalization. Four infections were caused by a vanB-type VRE t hat was genomically related to the ARE outbreak strain. The prescription ra te for vancomycin was low, but an increase in vancomycin use paralleled the appearance of VRE. The highest monthly incidence rate was 2.5 per 1000 pat ient admissions in July 1996 declining to 0.5 in December 1996. Conclusions The first nosocomial outbreak caused by ARE was observed in 199 5 in Norway and is still ongoing. One year after the onset, VRE occurred in wards which had a relatively high consumption of vancomycin.