title: Factors associated with geographic variations in stroke incidence among older populations in four US communities.
abstract: OBJECTIVE
  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 > or = 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.
authors.affiliation: Department of Epidemiology, University of Pittsburgh, 130 N Bellefield Ave, Rm 405, Pittsburgh, PA 15213, USA. amest30@pitt.edu
authors.forename: Aiman
authors.initials: A
authors.lastname: El-Saed
authors.forename: Lewis H
authors.initials: LH
authors.lastname: Kuller
authors.forename: Anne B
authors.initials: AB
authors.lastname: Newman
authors.forename: Oscar
authors.initials: O
authors.lastname: Lopez
authors.forename: Joseph
authors.initials: J
authors.lastname: Costantino
authors.forename: Kathleen
authors.initials: K
authors.lastname: McTigue
authors.forename: Mary
authors.initials: M
authors.lastname: Cushman
authors.forename: Richard
authors.initials: R
authors.lastname: Kronmal
mesh_terms: D000368:Aged; D001921:Brain / Q000473:pathology; D002140:California / Q000453:epidemiology; D005260:Female; D006801:Humans; D015994:Incidence; D008279:Magnetic Resonance Imaging; D008297:Male; D008396:Maryland / Q000453:epidemiology; D009657:North Carolina / Q000453:epidemiology; D010414:Pennsylvania / Q000453:epidemiology; D016016:Proportional Hazards Models; D018570:Risk Assessment; D012307:Risk Factors; D020521:Stroke / Q000453:epidemiology* / Q000209:etiology / Q000401:mortality / Q000473:pathology