Outbreak of infection with high-level gentamicin-resistant Enterococcus faecalis (HLGRE) in a Norwegian hospital

Objective To examine and characterize a suspected outbreak of high-level gentamicin-resistant Enterococcus (HLGRE) infection. Methods Eighty-nine patients with clinical infection diagnosed during hospital stay or within 30 days after discharge in the period from June 1995 to 31 December 1999 were included in the study. One control patient was assigned for each HLGRE patient according to localization in the hospital (same ward), time of admission (+/-3 months), and age (+/-10 years). Unadjusted risk analysis and multivariate logistic regression analysis were performed. Sixty-nine HLGRE strains were subjected to PCR amplification of the genes coding for aminoglycoside-3'-O -phosphoryltransferase-III (APH(3')-III) and aminoglycoside-6'-N -acetyltransferase/2''-O -phosphoryltransferase-III (AAC(6')/APH(2'')). Results The gene aacA/aphD , associated with HLGRE, was detected by PCR in all isolates, and the gene aphA3 , associated with high-level streptomycin, kanamycin and amikacin resistance, was detected in 56 of the 69 isolates. None of the 69 isolates was resistant to glycopeptides or ampicillin. Resistance to ciprofloxacin was found in 57 (82.6%). Pulsed-field gel electrophoresis analysis revealed 12 different genotypes, among which two major clusters dominated. Conclusions Both clonal expansion and the emergence of unique strains contributed to the increased number of infections caused by HLGRE. Urinary catheterization, duration of hospital stay and antibiotic therapy were significant risk factors for HLGRE infection.