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

Since January 1995 there has been a nosocomial outbreak at Haukeland Univer sity Hospital involving more than 330 patients with clinical infections cau sed by ampicillin-resistant Enterococcus faecium (ARE) (minimum inhibitory concentration greater than or equal to 32 mg/l). Rectal carriage of ARE was initially observed on two medical wards only. Here the ARE colonisation ra te has remained high. To assess risk factors for ARE colonisation we perfor med a case-control study including 37 rectal carriers of ARE and 83 non-car riers 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 < 0.001), mean number of diffe rent antibiotics prescribed (2.8 for carriers, 2.1 for non-carriers, p = 0. 008) and mean number of days in hospital (18.4 vs 10.2, p = 0.001). Unadjus ted statistical analysis showed that several antibiotics were risk factors for ARE carriage. Logistic regression analysis showed that fluoroquinolone prescription (OR = 3.5, p = 0.01) and more than 10 days of antibiotic use ( OR = 3.3, p = 0.01) were significant risk factors. An additional follow-up screening of previous carriers revealed no colonisation 8 to 36 (median 9) months after discharge from hospital(n = 17). Prolonged antimicrobial thera py and broad-spectrum antibiotics seem to facilitate nosocomial ARE colonis ation.