Outbreak of ampicillin-resistant Enterococcus faecium: risk factors for faecal colonisation

Since January 1995 there has been a nosocomial outbreak at Haukeland University Hospital involving more than 330 patients with clinical infections caused by ampicillin‐resistant Enterococcus faecium (ARE) (minimum inhibitory concentration ≥32 mg/l). Rectal carriage of ARE was initially observed on two medical wards only. Here the ARE colonisation rate has remained high. To assess risk factors for ARE colonisation we performed a case‐control study including 37 rectal carriers of ARE and 83 non‐carriers on these wards. Significant differences were found between cases and controls with respect to the mean number of days on antimicrobial treatment (13.3 for carriers, 5.5 for non‐carriers, p