Risk factors for isolation of low-level mupirocin-resistant versus -susceptible methicillin-resistant Staphylococcus aureus from patients in intensive care units

Objectives: The aim of this study was to determine the risk factors for the recovery of low-level mupirocin-resistant (mup^r) or -susceptible (mup^s) MRSA from patients in intensive care units (ICUs). Methods: A case-case-control study was conducted from November 2003 to April 2004. Two case groups consisted of patients with low-level mup^r MRSA and mup^s MRSA. A control group was frequency matched. Results: Mup^r MRSA and mup^s MRSA were isolated from 20 to 51 patients, respectively, during a six-month period. Risk factors identified for mup^r MRSA were as follows: exposure to piperacillin-tazobactam (odds ratio [OR] 13.8; 95% confidence intervals [CI], 1.8-105.0), third-generation cephalosporins (OR, 5.0; 95% CI, 1.6-15.5) and quinolones (OR, 3.4; 95% CI, 1.1-10.7). Risk factors identified for mup^s MRSA were as follows: length of ICU stay (OR, 1.1; 95% CI, 1.0-1.1), surgery (OR, 3.7; 95% CI, 1.5-9.0), exposure to third-generation cephalosporins (OR, 8.4; 95% CI, 3.3-21.7) and quinolones (OR, 7.7; 95% CI, 2.8-21.3). Conclusions: Our results suggest that nosocomial isolation of low-level mup^r MRSA may be affected by piperacillin-tazobactam.