Trend of vancomycin MIC values among MRSA clinical isolates and association with patient outcome

Abstract

Background: Methicillin-resistant Staphylococcus aureus (MRSA) has become a common cause of nosocomial and community-acquired infection. Vancomycin has become the drug of choice given the emergence of MRSA; however, studies have reported an increase in the vancomycin minimum inhibitory concentration (MIC) and vancomycin treatment failure despite MICs within the susceptible range ()2 μg/mL). Limited studies have examined whether this increase in vancomycin MIC is associated with patient outcome. Methods: We reviewed the medical records of patients diagnosed with MRSA bloodstream or lower extremity wound infection from January 1, 1998 through December 31, 2008. Bivariate and multivariate analyses were conducted to examine the association between vancomycin MIC and other covariates. Results: 97 patients were diagnosed with a MRSA infection; 65% (63/97) of patients had a bloodstream infection and 35% (34/97) of patients had a wound infection. From 1998 to 2003, MRSA with a low vancomycin MIC (≤1 μg/mL) were in the majority; however, from 2004 to 2008, MRSA with a high MIC (=2 μgg/mL) were in the majority. Therefore, over time, there was a significant upward trend in vancomycin MIC values (p = 0.01). Logistic regression analysis revealed that a high vancomycin MIC was significantly associated with a past medical history of malignancy (p = 0.04) and death within 30 days of infection (p = 0.04) compared to a low vancomycin MIC. Conclusion: Our study has shown (1) vancomycin MIC values have displayed an upward ‘creep’ over time, and (2) high MIC values of vancomycin is significantly related to a past medical history of malignancy as well as higher mortality within 30 days of MRSA infection. Further prospective studies are needed to examine the clinical significance of an upward ‘creep’ in vancomycin MIC values. Abstracts for SupplementInternational Journal of Infectious DiseasesVol. 14Preview Full-Text PDF Open Archive