Impact of a formulary switch from ticarcillin-clavulanate to piperacillin-tazobactam on colonization with vancomycin-resistant enterococci

Background The prevalence of vancomycin-resistant enterococci (VRE) is increasing, despite infection control measures. Limited data link ticarcillin-clavulanate to higher VRE prevalence. Methods Active surveillance for VRE was conducted before and after a formulary switch from ticarcillin-clavulanate to piperacillin-tazobactam. Rectal swabs were obtained serially in 863 adult patients admitted to intensive care units (ICUs) between November 1, 2000 and September 30, 2004. Results In the postswitch period, 38 of 497 (7.6%) patients acquired VRE versus 42 of 366 (11.5%) patients in the preswitch period. Survival analysis showed an overall hazard ratio (HR) of .68 postswitch versus preswitch (P = .07), with the greatest change in the surgical ICU (HR = .17, P = .006). Multivariate analysis showed an overall HR = .51 (P = .004). Hospital-wide, nonstool VRE clinical cultures fell from 39 (.58/1000 patient days) in the 10-month preswitch period to 27 (.33/1000 patient days) in the 12-month postswitch period. Infection control practices and use of other antibiotics remained stable. Conclusions VRE acquisition appeared to decrease in association with a formulary change from ticarcillin-clavulanate to piperacillin-tazobactam.