Risk factors associated with mupirocin resistance in meticillin-resistant Staphylococcus aureus

Implementation of meticillin-resistant Staphylococcus aureus (MRSA) decolonisation programmes has been increasing and the emergence of mupirocin resistance has been reported. However, the patient-level risk factors associated with mupirocin resistance are not clear. In this study, independent predictors of mupirocin resistance in MRSA among Providence Veterans Affairs Medical Center patients with MRSA-positive culture dates between 1 July 2004 and 30 June 2008 were identified using a frequency-matched case-control study. Forty cases (mupirocin-resistant) were matched on culture date quarter and year to 270 controls (mupirocin-susceptible). The adjusted conditional logistic regression model identified three significant independent predictors associated with mupirocin resistance in MRSA: (1) exposure to mupirocin in the year prior to the culture date [odds ratio (OR): 9.84; 95% confidence interval (CI): 2.93-33.09]; (2) Pseudomonas aeruginosa infection in the year before the culture-related admission (4.85; 1.20-19.61); and (3) cefepime use in the year prior to culture (2.80; 1.03-7.58). In sensitivity analyses, previous mupirocin exposure was associated with low-level [minimum inhibitory concentration (MIC) 8-128 mg/L; 23 cases, 202 controls; OR: 6.32; 95% CI: 1.58-25.33] and high-level (MIC >= 256 mg/L; 17 cases, 151 controls; OR: 11.18; 95% CI: 1.89-66.30) mupirocin resistance. To our knowledge, this is the first case-control study to reveal a strong association between previous mupirocin exposure and subsequent mupirocin resistance in MRSA, with demonstrated robustness in low- and high-level mupirocin resistance. Mupirocin susceptibility monitoring is critical for facilities instituting decolonisation with mupirocin as increased use may reduce effectiveness through resistance. (C) 2010 The Hospital Infection Society. Published by Elsevier Ltd. All rights reserved.