Copyright ©) 1993, American Society for Microbiology Epidemiologic Analysis and Genotypic Characterization of a Nosocomial Outbreak of Vancomycin-Resistant Enterococci

We are reporting on a nosocomial outbreak of 213 cases of vancomycin-resistant enterococcus infection involving 2,812 enterococcal isolates from patients over a period of 36 months. In 1990, the Enterococcus faecium vancomycin susceptibility rate was found to be 85.7 % (36 of 42 cases), and an incidence of 10.9%o (42 of 383) was noted. The 1991 data showed E.faecium with a vancomycin susceptibility rate of61.8 % (110 of 178) and an incidence of 26.0%,o (178 of 684). Subsequently, in 1992, the incidence ofE.faecium increased to 34.0%yV (599 of 1,745), with a decreased vancomycin susceptibility rate of 25.8 % (155 of 599). The E. faecalis vancomycin susceptibility rate remained near 97 % (1,768 of 1,823) over the 36-month period. Of 115 vancomycin-resistant enterococcus (VRE) clinical isolates identified by the MicroScan MIC Combo-6 panels (Baxter Healthcare, Sacramento, Calif.), the agar dilution method indicated the resistance rate to be 92.3% (106 of 115) (high level), 3.5 % (4 of 115) midlevel, and 3.5 % (4 of 115) (low level). Genotypic characterization of 32 different VRE isolates by field-inversion gel electrophoresis demonstrated 19 dissimilar restriction endonuclease patterns, with 9 patterns associated with VRE quinolone resistance. Statistical analysis of case-control data for 32 patients with VRE infections indicated a positive association with intrabdominal surgical procedures (odds ratio, 24.12), multidrug therapy (odds ratio, 37.80), preexposure to vancomycin (odds ratio, 20.21), and death (odds ratio, 17.50)