A nationwide study of comorbidity and risk of reinfection after Staphylococcus aureus bacteraemia

Background: Data on risk factors and rates of reinfection associated with Staphylococcus aureus bacteraemia (SAB) are sparse. Methods: We conducted a nationwide cohort study of cases of SAB diagnosed between 1995 and 2008. Reinfection was defined as an episode of SAB more than 90 days after the initial episode of SAB. Comorbidity was evaluated by the Charlson Comorbidity Index (CCI). Cox proportional hazards modelling was used to estimate hazard rates (HR). Results: Of 10,891 eligible patients, 774 (7.1%) experienced reinfection a median of 458 days (range 90-5021 days) after their primary SAB episode corresponding to a reinfection rate of 1459 (95% confidence interval (CI): 1357-1562) per 100,000 personyears. In multivariate analysis, sex, origin, a vascular or peritoneal device, endocarditis and comorbidity were associated with reinfection. The association was more than two-fold higher among patients in dialysis and for patients with severe comorbidity (CCI≥2). HIV infection (Hazard ratio (HR) 6.18, 95% CI: 4.17-9.16), renal disease (HR 3.92, 95% CI: 3.22-4.78), diabetes with complications (HR 2.11, 95% CI: 1.69-2.62), diabetes without complications (HR 1.61, 95% CI: 1.34-1.93), mild (HR: 1.94, 95% CI: 1.36-2.76) and severe liver disease (HR 2.08, 95% CI: 1.08-4.03), peptic ulcer (HR 1.33, 95% CI: 1.03-1.72), and paraplegia (HR 2.15, 95% CI: 1.02-4.54) were each associated with an increased risk of reinfection. Conclusions: Patients with previous SAB have a 60-fold higher risk of SAB compared to the general population. Patients with HIV infection, renal disease, diabetes, liver disease, peptic ulcer and paraplegia had the highest rates of reinfection.