Prediction model to identify patients with Staphylococcus aureus bacteremia at risk for methicillin resistance

OBJECTIVES: To identify institution-specific risk factors for MRSA bacteremia and develop an objective mechanism to estimate the probability of methicillin resistance in a given patient with Staphylococcus aureus bacteremia (SAB). DESIGN: A cohort study was performed to identify institution-specific risk factors for MRSA. Logistic regression was used to model the likelihood of MRSA. A stepwise approach was employed to derive a parsimonious model. The MRSA prediction tool was developed from the final model. SETTING: A 279-bed, level 1 trauma center. PATIENTS: Between January 1, 1999, and June 30, 2001, 494 patients with clinically significant episodes of SAB were identified. RESULTS: The MSRA rate was 45.5%. of 18 characteristics included in the logistic regession, the only independant features for MRSA were prior antibiotic exposure (OR, 9.2; CI95, 4.8 to 17.9), hospital onset (OR, 3.0; CI (95), 1.9 to 4.9), history of hospitalization (OR, 2.5; CI95, 1.5 to 3.8), and presence of decubitus ulcers (OR, 2.5; CI95, 1.2 to 4.9). The prediction tool was derived from the final model, which was shown to accurately reflect the actual MRSA distribution in the cohort. CONCLUSION: Through multivariate modeling techniques, we were able to identify the most important determinants of MRSA at our institution and develop a tool to predict the probability of methicillin resistance in a patient with SAB. This knowledge can be used to guide empiric antibiotic selection. In the era of antibiotic resistance, such tools are essential to prevent indiscriminate antibiotic use and preserve the longevity of current antimicrobials.