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Factors of Premature Mortality Disparities Due to Stroke Identified

The county with the highest premature stroke mortality was 20.78 times higher than that of the county with the lowest mortality. The data have raised alarms among the study authors.

Data from a retrospective, cross-sectional study showed a decrease in premature stroke mortality from 1999 to 2018, but with between-county disparities still present, suggesting that strategies should address specific factors that underlie mortality disparities, especially out-of-stroke-unit deaths and strokes of uncertainty.

Lead author Suhang Song, PhD, associate research scientist, Columbia University Irving Medical Center, and colleagues linked the mortality and demographic data of 2637 US counties from the Centers for Disease Control and Prevention WONDER database to county-level characteristics from multiple databases. Demographic composition, socioeconomic status, health care and environmental factors, and population health, were identified as associated with county-level mortality and were investigated using generalized linear Poisson regressions.

The primary outcome measure was county-level-adjusted stroke mortality among adults aged 25 to 64 years from 1999 to 2018. During that span, the mortality rates did not change substantially (from 12.62 to 11.81 per 100,000 population); however, the proportions of death due to stroke occurring outside of the stroke unit increased from 23.56% (4328 of 18,369) to 34.57% (6978 of 20,188). Intracerebral hemorrhage was the leading cause of death, with a rate of 4.29 per 100,000 population, and a rate of 3.80 per 100,000 population for deaths not specified as caused by hemorrhage or infarction.

Theil index score, calculated to assess the mortality disparities, was 0.091 for county-level mortality and was broken down by between-state and within-state variation. Of this, within-state variation accounting for 51.5% (within-state Theil index score, 0.047; overall Theil index score, 0.091) of the overall disparities.

READ MORE: Intracerebral Hemorrhage Linked to Increased Risk of Ischemic Stroke, Myocardial Infarction

During 1999 to 2018, the county with the highest mortality was 20.78 times higher than the county with the lowest mortality (65.04 vs 3.13 deaths per 100,000 population). Geographically, the highest mortality was observed in counties within the southeastern stroke belt band, stretching from the Ohio River Valley to the Mississippi River Valley.

Song and colleagues documented that the Theil index score for out-of-stroke-unit death was 0.135, which was higher than that for in-hospital death at 0.092. Within-state variation accounted for 57% (Theil index score, 0.077) of the overall disparity (Theil index score, 0.135) for out-of-stroke-unit death.

"The findings of this study provide insight into which features may predispose certain counties to stroke mortality disadvantage. We highlighted the large percentage reporting stroke not specified as hemorrhage or infarction, with the majority of deaths occurring out of the stroke unit,” Song et al wrote. Using dominance analysis, demographic composition, population health, health care and environmental features, and socioeconomic status, were 29.4%, 28.2%, 22.7%, and 19.6% associated with premature stroke mortality, respectively.

For out-of-stroke-unit death, county-level premature stroke mortality was associated with demographic composition (31.6%) and health care and environmental features (25.8%). Population health accounted for 29.8% of county-level mortality for in-hospital death, whereas 28.7% accounted for demographic composition.

The percentage of rural residents, percentage of those older than 64 years, percentage of Black of African American individuals, percentage of Asian individuals, uninsured rate, and prevalence of physical inactivity were all positively associated with both out-of-stroke-unit and in-hospital death rates. Negative associations for mortality for both out-of-stroke-unit and in-hospital death rates were observed for the percentage of individuals born outside the US, income, and health care quality index.

Researchers also noticed that factors associated with county-level mortality varied by stroke subtypes. Each of these subtypes had premature stroke mortality associated with demographic composition. The percentage of rural residents were positively associated with mortality of each subtype, whereas the percentage of American Indian or Alaskan Native individuals, the percentage of individuals born outside the US, median household income, and health care quality index were negative associated with mortality for both intracerebral hemorrhage and those not specified as hemorrhage or infarction.

Song S, Ma G, Trisolini MG, et al. Evaluation of between-county disparities in premature mortality due to stroke in the US. JAMA Netw Open. Published online May 12, 2021. doi: 10.1001/jamanetworkopen.2021.4488