Infections by ampicillin-resistant enterococci: a case-control study.

We identified 17 (20%) of 83 consecutive enterococcal isolates from hospitalized patients with documented infection as high-level ampicillin-resistant enterococci (ARE). Of these, 16 isolates were identified as Enterococcus faecium and 1 isolate as Enterococcus raffinosus. A case-control study found no significant differences with respect to underlying diseases, central venous catheterization, nosocomial acquisition of the infection and sites of infection. Patients with ARE infection were older and had a higher inhospital fatality rate than those with ampicillin-susceptible Enterococcus (ASE) infection. Hospitalization in a surgery service (usually for an abdominal procedure), prolonged hospital stay, prior treatment with antibiotics (in particular imipenem and metronidazole), were also more frequent among patients with ARE infection. ARE isolates were more frequently resistant to imipenem, ciprofloxacin and streptomycin than ASE isolates.