VARIATIONS IN STROKE INCIDENCE IN FOUR US COMMUNITIES:THE CARDIOVASCULAR HEALTH STUDY (CHS)

BACKGROUND: Although stroke rates are much higher in old age, recent data on geographic variation in stroke incidence in older American populations were rare. Moreover, geographic variation in stroke incidence and mortality remain unexplained in United States.OBJECTIVES: To compare stroke incidence rates and stroke risk factors and their control in four US communitiesMETHODS: Participants in the Cardiovascular Health Study (CHS) who had no history of stroke at baseline (n=5639) were followed for 10 years for the development of stroke events. Site specific stroke incidence and mortality rates were calculated. Possible risk factors at baseline and their control across the visits were compared among the four CHS sites. RESULTS: Age and sex standardized total stroke incidence rates per 1000 person-years were 9.6 (CI 7.7, 11.5) in Allegheny, 19.2 (CI 15.6, 22.8) in Forsyth, 20.7 (CI 16.9, 24.5) in Sacramento, and 19.8 (CI 16.1, 23.5) in Washington Counties. Although Allegheny County had the lowest stroke incidence among the 4 sites, risk factor distributions at baseline were similar. After adjustment for age, hypertension, diabetes, education, BMI, LDL cholesterol and previous coronary heart disease, transient ischemic attack (TIA), and atrial fibrillation (AF), there was modest reduction of the excess hazard in the other 3 sites compared to Allegheny County (HR=1.52, CI 1.17, 1.98 compared to 1.74 CI 1.42, 2.14). Moreover, between baseline and year 9, control of hypertension, diabetes, lipids, smoking, AF, and TIA were similar across sites. White matter grade (WMG) 3 or more on the baseline brain MRI was less common in Allegheny County than the other 3 sites (25.8%and 36.3% respectively, p< 0.001) and accounted for 25% of the excess hazard in the other 3 sites compared to Allegheny County (HR=1.65, CI 1.20-2.26 compared to 1.87 CI 1.36-2.55) CONCLUSION: Site-differences in stroke risk factors at baseline and their subsequent control only partially explain site-differences in stroke incidence. PUBLIC HEALTH SIGNIFICANCE: White matter grade may be a marker of integrated exposure and control of stroke risk factors and its progression could be used as a marker of the efficacy of different stroke prevention strategies on a community level