O16 - Can nasal methicillin-resistant Staphylococcus aureus screening be used to avoid empiric vancomycin use in intra-abdominal infection?

Puja Shah, Sara Hennessy, Christopher Guidry, Robert Sawyer, Stephen Davies, Tjasa Hranjec, University of Virginia

Background: Vancomycin is widely used as empiric therapy for gram-positive organisms in patients with an intra-abdominal infection (IAI), even in those with no history of methicillin-resistant Staphylococcus aureus (MRSA) infection or colonization. Potential adverse effects of vancomycin include nephrotoxicity, increased cost and bacterial resistance.

Hypothesis: We hypothesized that nasal screening could be used to predict patients with MRSA IAI and used to avoid unnecessary empiric vancomycin use.

Methods: A prospectively collected surgical infections database from a single institution was reviewed for all IAI between January 1, 2000 and December 31, 2011. Patients with and without MRSA obtained from abdominal cultures as either a monomicrobial or polymicrobial isolate were compared by univariate analysis using Wilcoxon rank sum, Chi-square, and fisher’s exact tests where appropriate. A multivariate logistic regression was performed to identify independent predictors of MRSA IAI.

Results: MRSA nasal screening (pre-IAI) data was available for 387 patients of 2591 patients with an IAI. Patients with MRSA IAI (n = 48) had higher rates of diabetes, Crohn’s disease, and positive MRSA nasal screenings, along with lower white blood cell counts and rates of recent surgery compared to those with non-MRSA IAI. Mortality was similar between MRSA and non-MRSA IAI, 1/48 (2.1%) versus 18/339 (5.3%), respectively (p = 0.49). On multivariate analysis (c-statistic = 0.89), the strongest independent predictor of an MRSA IAI was a positive MRSA screen (OR 36.5, CI 14.4-92.4), followed by Crohn’s disease (OR 3.76, CI 1.2-11.6), and diabetes (OR 2.5, CI 1.1-5.7). The positive predictive value for a MRSA screen was 42% while the negative predictive value of MRSA screening was 98%.

Conclusions: A negative MRSA nasal screen indicates with near certainty the absence of MRSA as part of intra-abdominal infection. In the setting of a recent screen, empiric vancomycin can be withheld. Further, rapid MRSA nasal screening could be used to forego or to rapidly discontinue vancomycin therapy in the setting of IAI. This change in empiric antibiotic management of intra-abdominal infections may lead to decreased morbidity, reduction in costs, and a decrease in bacterial resistance.