Previous infection and other risk factors for acute cerebrovascular ischaemia: attributable risks and the characterisation of high risk groups.

Background: Recent reports indicated that previous infection may be a risk factor for ischaemic stroke in younger adults and that the increased mortality of cerebrovascular diseases in winter months may be partly caused by the increased rate of infection during the cold season.

Methods: We performed a 1:1 matched case-control study with 197 cases (83 females, 114 males) aged between 22 and 80 years (median age 65 years) to investigate risk factors for acute cerebrovascular ischaemia, in particular the effect of previous infection. We estimated the impact of risk factors in terms of attributable and absolute risks.

Results: All risk factors together, previous infection, hypertension, diabetes mellitus, smoking, coronary heart disease, previous stroke or transient ischaemic attack and family history of stroke yield a summary attributable risk of 0.74 [95% confidence intervals (CI) 0.64-0.83]. Recent infections showed a relative risk of 4.3 (95% CI 1.8-10.5) and an attributable risk of 0.15 (95% CI 0.09-0.21). Seventeen percent of the German population are estimated to be in a high-risk group. This subgroup contributes about 55% of the estimated yearly 120,000 incident cases in the age group 55-84 in Germany.

Discussion: Identification of high-risk groups for stroke on the basis of individual risk factor distribution and the estimation of its size is possible and may produce useful results. Reducing the prevalence of infection and early treatment of bacterial infection may lower the incidence of stroke.