We determined the association between the use of the glycopeptide antibiotic avoparcin as a growth promoter and the occurrence of Enterococcus faecium (VREF) with high-level resistance to vancomycin (MIC ≥ 64 μg ml−1) on poultry and pig farms. The investigations were conducted as retrospective cohort studies, where groups of farms exposed or not exposed to avoparcin between September 1994 and April 1995 were compared.
