Social Determinants of Health and Fatal Crashes Involving US Geriatric and Non-Geriatric Road Users

IntroductionSocial determinants of health (SDoH), defined as nonmedical factors that impact health outcomes, have been associated with fatal crash occurrences. Road users who live in communities with negative SDoH may be at increased risk of crash-related mortality, and the risks may be further heightened among geriatric road users and in rural areas. We evaluated the relationship between the county-level measure of SDoH and county-level fatal crash counts among geriatric and non-geriatric road users living in rural, suburban, and urban areas. MethodsFor this ecological study, we pooled data from Fatality Analysis Reporting System (2018 to 2020) and the U.S. Census Bureau (2019 data) and limited our analyses to the 3,108 contiguous US counties. The outcome measures were county-level fatal crash counts involving (1) geriatric (65 years and older) road users (2) non-geriatric road users, and (2) the general population. The predictor variable was the Multidimensional Deprivation Index (MDI), a score that measures the five domains of SDoH - economic quality, healthcare access, education, community, and neighborhood quality. We defined the MDI as a three-level categorical variable: at or below the national average, within two-fold of the national average, and higher than two-fold of the national average. We controlled for county-level demographics and crash characteristics. We performed a Bayesian spatial Poisson regression analysis using Integrated Nested Laplace Approximations and reported the crash fatality rate ratios (plus 95% Credible Intervals (CrI)). ResultsThe median (Q1, Q3) standardized mortality rate ratios among geriatric and non-geriatric road users were 1.3 (0.6, 2.5) and 1.6 (0.9, 2.7), respectively. A total of 283 (9.1%) and 806 (15.9%) counties were classified as very highly deprived and highly deprived, respectively. Clusters of counties with high deprivation rates were identified in the Southern states. Counties classified as very highly deprived and highly deprived had 40% (95% CrI: 1.24 - 1.57) and 25% (95% CrI: 1.17 - 1.34) increased geriatric fatality crash rate ratios and this pattern of association persisted in suburban and urban areas. Also, counties classified as very highly deprived and highly deprived had 42% (95% CI: 1.27 - 1.58) and 32% (95% CI: 1.23 - 1.38) increased fatality crash rate ratios among all road users and this pattern persisted in suburban and urban areas. Counties with more than four-fold increased fatality rate ratios were located commonly in Texas, Oklahoma, Nevada, and Utah. ConclusionDespite older adults being less frequent road users, county-level deprivation measures of the SDoH are equally associated with geriatric and non-geriatric crash-related fatal rate ratios. Policies that improve county-level SDoH may reduce the county-level fatal rate ratios equally among geriatric and non-geriatric road users.