Poor Functional Status Is an Independent Predictor of Surgical Site Infections Due to Methicillin-Resistant Staphylococcus aureus in Older Adults

BACKGROUND Methicillin-resistant Staphylococcus aureus (MRSA) has become a common surgical site infection (SSI) pathogen, particularly in older adults. Risk factors for MRSA SSI in elderly patients have not been described. METHODS A nested case-control study was conducted. Patients were enrolled from seven study hospitals (one medical center and six community hospitals) between January 1, 1998, and April 1, 2003. Risk factors for MRSA SSI were identified by comparing cases with two reference groups: uninfected surgical patients and patients with SSI due to methicillin-susceptible S. aureus (MSSA). Two separate multivariate models were created using logistic regression and then compared and contrasted. RESULTS Eighty-six patients with MRSA and 64 with MSSA SSI were identified. One hundred sixty-seven uninfected surgical patients were selected. In multivariate analysis using uninfected surgical patients as controls, requiring assistance in three or more activities of daily living (ADLs) was an independent risk factor for MRSA SSI (odds ratio (OR)=2.73, 95% confidence interval (CI)=1.16-6.46). Using patients with MSSA SSIs as a reference group, requiring assistance in three or more ADLs was also a significant predictor for MRSA SSI (OR=3.78, 95% CI=1.43-9.98) in multivariate analysis. Other independent predictors included Charlson score, wound class, and surgical duration. Lack of independence in ADLs was an independent risk factor for MRSA SSI in elderly patients in both models. CONCLUSION Poor functional status (requiring assistance in >= 3 ADLs) was specifically associated with MRSA SSI. Functional status is an objective, readily available variable that can be used to stratify patients at risk for MRSA SSI.