Nosocomial outbreak of ampicillin resistant Enterococcus faecium: Risk factors for infection and fatal outcome

A nosocomial outbreak caused by ampicillin resistant Enterococcus faecium ( ARE) was detected at a Norwegian university hospital in January 1995. Prior to this outbreak, ARE were not common in this hospital or other hospitals in Norway. During 1995 and 1996, a total of 149 cases with clinical ARE inf ection were detected prospectively. A case control study was performed by a llocating controls matched for gender, age and ward of admission. Altogethe r, 123 case control pairs with mean age 70.1 years were included. Isolates from 89 (72.4%) of the cases were identical or related to the defined outbr eak strain as determined by pulsed-field gel electrophoresis (PFGE). In 75 of the patients (60.9%), ARE caused urinary tract infection, five (4.1%) ha d bacteraemia, 33 (26.8%) had wound infection and 10 (8.1%) had other infec tions. In a logistic regression model for 1:1 matched samples, the followin g factors were identified as significant risk factors for ARE infection: un derlying neurological disease (OR = 33.5), prescription of antimicrobial ag ents for more than 10 days (OR = 8.99), prescription of cephalosporins (OR = 4.69), underlying gastrointestinal disease (OR = 3.36) and length of hosp ital stay per day (OR = 1.04). The intrahospital death rate for the cases w as 18.7% compared with 8.9% for the controls, corresponding to an excess mo rtality attributable to ARE infection of 9.8%. A history of carbapenem pres cription was the only independent factor contributing to death (OR = 5.64) when comparing ARE patients dying in hospital to those surviving. (C) 2000 The Hospital Infection Society.