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

OBJECTIVES

To describe the first nosocomial outbreak of ampicillin-resistant Enterococcus faecium (ARE) in Norway, where a few vancomycin-resistant strains have also been identified.

METHODS

All cases of ARE and vancomycin-resistant Enterococcus faecium (VRE) diagnosed by the medical microbiological laboratories in a region inhabited by approximately 1 million people were registered. Isolates obtained during the period 1 January 1995 to 31 December 1996 were characterized by pulsed 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 genomically related to the outbreak strain. Infections included bacteremia (14), wound infections (31), urinary tract infections (97) and other infections (seven). Most had a severe underlying disease and 93% of the patients had received antibiotics for a mean time of 23 days. Twenty-four patients (16.1%) died during hospitalization. Four infections were caused by a vanB-type VRE that was genomically related to the ARE outbreak strain. The prescription rate 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 patient admissions in July 1996 declining to 0.5 in December 1996.

CONCLUSIONS

The first nosocomial outbreak caused by ARE was observed in 1995 in Norway and is still ongoing. One year after the onset, VRE occurred in wards which had a relatively high consumption of vancomycin.