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(Stroke. 2006;37:1980.)
© 2006 American Heart Association, Inc.

Original Contributions

Factors Associated With Geographic Variations in Stroke Incidence Among Older Populations in Four US Communities

Aiman El-Saed, MD, PhD, MPH; Lewis H. Kuller, MD, DrPH; Anne B. Newman, MD, MPH; Oscar Lopez, MD; Joseph Costantino, DrPH; Kathleen McTigue, MD, MS, MPH; Mary Cushman, MD, MSc Richard Kronmal, PhD

From the Department of Epidemiology (A.E., L.H.K., A.B.N.) University of Pittsburgh, Pa; the Department of Neurology (O.L.), University of Pittsburgh, Pa; the Department of Biostatistics (J.C.), University of Pittsburgh, Pa; Department of General Medicine (K.M.), University of Pittsburgh, Pa; the Department of Medicine (M.C.), University of Vermont, Colchester, Vt; and the Department of Biostatistics (R.K.), University of Washington, Seattle, Wash.

Correspondence to Aiman El-Saed, MD, PhD, MPH, Department of Epidemiology, University of Pittsburgh, 130 N Bellefield Ave, Rm 405, Pittsburgh, PA, US 15213. E-mail amest30{at}pitt.edu

Background and Purpose— In the Cardiovascular Health Study (CHS), we previously observed lower stroke incidence in Allegheny County, PA compared with the other 3 study sites. The purpose of this study was to study possible reasons for the lower stroke incidence in Allegheny County.

Methods— CHS participants 65 years or older who were stroke-free at baseline (n=5639) were followed between 1989 to 1990 and 2000 for the development of stroke. Risk factors at baseline and their subsequent control were compared among both groups. Site-specific hazard ratios for stroke incidence were calculated using Cox regression models.

Results— The unadjusted hazard ratio for total stroke incidence in Forsyth County, NC; Sacramento County, CA; and Washington County, MD combined compared with Allegheny County, PA was 1.74 (95% CI: 1.42, 2.14). After adjustment for age and other traditional risk factors, there was modest reduction of the excess hazard in non-Allegheny sites compared with Allegheny County (hazard ratio=1.52, 95% CI: 1.17, 1.98). Between baseline and the seventh-year visits, control of hypertension, diabetes, lipids, smoking, atrial fibrillation and transient ischemic attack were similar across sites. White matter grade 3 on the baseline brain MRI was less common in Allegheny County (25.8% versus 36.3%, respectively; P<0.001) and accounted for 25% of the excess hazard in non-Allegheny sites compared with Allegheny County.

Conclusions— Site differences in stroke risk factors at baseline and subsequent control only partially explain site differences in stroke incidence. White matter grade as a possible integrated measure of exposure and control of risk factors may help in explaining geographic variations in stroke incidence.

Key Words: epidemiology • geography • incidence • magnetic resonance imaging • risk factors • stroke

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