Case-control study to identify factors associated with mortality among patients with methicillin-resistant Staphylococcus aureus bacteraemia

Methicillin-resistant Staphylococcus aureus (MRSA) bacteraemia is associated with increased mortality. Delay in appropriate antimicrobial therapy (DAAT) is an important risk factor for death, although confounding between carriage of MRSA and DAAT has not been resolved. We studied the association of risk factors with mortality and searched for specific populations vulnerable to DAAT. We conducted a case-control study comparing patients with MRSA bacteraemia who died during hospitalization (cases) with patients with MRSA bacteraemia who survived (controls) in three medical centres in two states. Patients were identified using computerized hospital databases for the years 2001-2005. Medical records were retrieved and various epidemiological data extracted. Bivariate and multivariate logistic regression analyses were performed. Overall, 388 patients with MRSA bacteraemia were included, 164 cases and 224 controls. According to bivariate analyses, cases were significantly more likely than controls to (i) be older (>65 years), (ii) have transferred from an institution, (iii) have stayed in an ICU, (iv) have had more invasive devices, (v) have a poorer prognosis on admission, (vi) have higher disease severity at the time of bacteraemia, and (vii) have a DAAT of ≥2 days. Upon multivariate analysis, among patients >65 years, DAAT was significantly associated with increased mortality (p 0.04). Furthermore, patients >65 years with severe sepsis were much more likely to experience DAAT (p 0.02). In elderly patients with MRSA bacteraemia, DAAT is associated with increased mortality. Moreover, advanced age is a predictor for DAAT. These significant epidemiological associations mandate early coverage of MRSA in septic elderly patients.