Of the 30,239 REGARDS participants, follow-up was available on 29,648 (98%). Of these, 1,886 (6%) with self-reported history of physician-diagnosed stroke at baseline were excluded. A total of 14 participants were excluded due to uncertain start of follow-up, 4 were excluded who had a stroke between their baseline telephone interview and in-home visit, resulting in an analysis cohort of 27,744. Demographic characteristics and baseline stroke risk factors by incident stroke status are provided in .
Characteristics of REGARDS Population by Incident Stroke Status
As of May 24, 2010, medical records and/or proxy interviews were sought on 4,410 suspected stroke events from 3,255 participants. Of these events, records were successfully reviewed for 3,417 (77.5%), still in process for 512 (11.6%), and could not be obtained for 481 (10.9%). The primary reason for inability to obtain medical records was participant or proxy declining to return a requested Health Insurance Portability and Accountability Act (HIPAA)-compliant hospital-specific authorization form. Among 3,417 suspected events with completed adjudication, there were 488 (14.3%) incident stroke events among 460 participants over a median follow-up of 4.4 years: 383 WHO strokes, 103 clinical strokes, and 2 probable strokes. In addition, 162 (4,7%) were adjudicated as TIAs and 2,767 (80.9%) as none-vents. Among the 488 strokes, only first ischemic stroke, first hemorrhagic stroke, or first nonspecific stroke for a participant was retained, yielding 464 cases. Four participants had 2 different types of strokes; 2 had ischemic stroke then hemorrhagic stroke, 1 had hemorrhagic stroke then ischemic stroke, 1 had hemorrhagic stroke then nonspecific stroke. Of the 460 participants with incident stroke, 384 (82.7%) were ischemic, 53 (11.4%) hemorrhagic, and 27 (5.8%) nonspecific ().
Number of Participants with an Incident Stroke Event and Person-Years of Observation by Type of Stroke, Race, and Sex
provides estimated age-race-sex–adjusted stroke incidence rates per 100,000 person-years. For all strokes, the highest rate was in the stroke buckle (614/100,000 person-years), followed by the stroke belt (547/100,000), then the non–stroke belt (517/100,000). Compared to area outside the stroke belt, the IRR was 1.06 (95% CI, 0.87–1.29) in the stroke belt and 1.19 (95% CI, 0.96–1.47) in the stroke buckle, differences that were not statistically significant. The regional pattern and magnitude of differences were similar for ischemic stroke; however, for hemorrhagic stroke, there was no trend among regions, with rates ranging from 68 in 100,000 in the stroke belt to 70 in 100,000 in the non–stroke belt. As anticipated, sensitivity analyses restricted to only WHO strokes provided incidence estimates generally 25% below those provided in (reflecting the exclusion of approximately 25% of strokes identified as clinical strokes); however, estimates of relative risk were not substantially affected by the restriction (data not shown.)
Estimated Stroke Incidence Rate (per 100,000 person-years) and Incidence Rate Ratio (with 95% CI) for all Stroke, Cerebral Infarction, and Hemorrhagic Stroke
Overall, the black-white sex-adjusted IRR () for all strokes was 1.51 (95% CI, 1.26–1.81); however, the magnitude of racial disparity differed significantly by age (pinteraction = 0.04). The highest black-white sex-adjusted IRR was for the youngest age group, 45–54 years (4.02; 95% CI, 1.23–13.11), with IRRs monotonically lower in each increasing age group, so there was no racial disparity for participants age ≥85 years (IRR 0.86; 95% CI, 0.33–2.20).
contrasts regional and racial differences in all stroke mortality for blacks and whites aged ≥45 years from CDC data to regional and racial IRRs calculated from REGARDS. For both region (see ) and race (see ), the pattern for CDC mortality and REGARDS incidence was similar. The magnitude of differences in stroke incidence was approximately one-half of the magnitude of differences in stroke mortality. Likewise, the pattern of greater racial disparities at younger ages was present for both REGARDS stroke incidence and CDC stroke mortality. In the youngest age stratum (45–54 years), the estimated REGARDS IRR was greater than the CDC MRR (4.02 vs 3.47); however, the magnitude of disparity in incidence was only approximately one-half of that observed for mortality for all other age strata. Only for age strata 55–64 years and 65–74 years did 95% CIs of IRRs not include the CDC MRR. For comparisons across regions, the MRRs were within the 95% CIs for IRRs observed in REGARDS.
FIGURE 2 Comparison of stroke MRRs calculated from U.S. death statistics, and IRRs calculated from REGARDS; 95% confidence intervals are provided for the IRR estimates from REGARDS but the MRRs are based on all deaths over the age of 45 years in the United States (more ...)