Case-control study of the relationship between MRSA bacteremia with a vancomycin MIC of 2 microg/mL and risk factors, costs, and outcomes in inpatients undergoing hemodialysis

Abstract

Background: An increased prevalence of bacteremia caused by methicillin-resistant Staphylococcus aureus (MRSA) with a vancomycin hydrochloride MIC of 2 microg/mL was noted in a population of inpatients undergoing hemodialysis at Baptist Memorial Health Care, Memphis, Tennessee.

Objectives: The aims of this study were to determine risk factors for infection with MRSA and to assess the differences in clinical and economic outcomes in patients undergoing hemodialysis with MRSA bacteremia with vancomycin MIC 2 microg/mL versus those with MRSA bacteremia with vancomycin MIC < or =0.5 microg/mL and uninfected controls.

Methods: This retrospective case-control study was conducted at Baptist Memorial Health Care. The study population (inpatients undergoing hemodialysis for MRSA bacteremia with vancomycin MIC 2 microg/mL [high-MIC group], MIC < or = 0.5 microg/mL [low-MIC group], and uninfected controls) was identified. Risk factors and clinical and economic outcomes (costs of hospitalization, nursing, and pharmacy) were determined and compared using univariate and multivariate statistics.

Results: Fifty patients with MRSA bacteremia undergoing hemodialysis were identified during the study period (high-MIC group, 17 [11 women, 6 men; mean (SD) age, 60 (17) years]; low-MIC group, 33 [23 women, 10 men; mean (SD) age, 62 (14) years]) and matched with 100 uninfected controls (57 men, 43 women; mean [SD] age, 63 [15] years). Risk factors for MRSA bacteremia found to be associated with high MIC included female sex, higher body mass index (1-point increments), recent surgery, and a history of cardiovascular disease (P < 0.05, P < 0.046, P = 0.04, and P = 0.028, respectively) (multivariate analysis). In the outcomes analysis, mortality was significantly higher in the high-MIC group compared with those in the low-MIC and control groups (35% vs 24% and 15%, respectively; P = 0.022). Total mean (SD) hospitalization costs were significantly higher in the high-MIC group compared with those in the low-MIC group and controls (US $47,624 [$80,534] vs $26,792 [$25,167] and $13,185 [$15,568], respectively; P < 0.001). Nursing costs were almost 6-fold higher in both infected groups compared with those in controls. Pharmacy costs in the low- and high-MIC groups were 3- to 6-fold higher, respectively, compared with those in controls.

Conclusions: Surgery within the previous 6 months and intensive care unit admission were identified as significant risk factors for patients with MRSA bacteremia with a vancomycin MIC 2 microg/mL undergoing hemodialysis. These patients experienced a longer mean hospital length of stay and increased hospital costs compared with patients with MRSA bacteremia with a vancomycin MIC < or =0.5 microg/mL and uninfected controls.