Beyond composite measures of regional vulnerability: Rural-urban colorectal cancer mortality disparities mediated by area-level characteristics.

[BACKGROUND] Rural-urban disparities in colorectal cancer (CRC) mortality have been attributed to individual- and population-level factors. Population-level composite measures such as the Social Vulnerability Index (SVI) have been used to investigate rural-urban disparities. However, the contribution of each SVI component to CRC mortality disparities among rural and urban counties is unknown.

[METHODS] Via CRC mortality data for all US counties from 1999 to 2020 from the Centers for Disease Control and Prevention, rural-urban differences in county demographics and in 14 SVI factors were examined. Four-way effect decomposition was used to estimate the proportion of the rural-urban CRC mortality disparity mediated by the SVI.

[RESULTS] Among 2927 counties (rural, 60.7%; urban, 39.3%), rural counties had 11.8% higher CRC mortality than urban counties; 18.6% of that disparity was mediated by low socioeconomic status (SES), 8.8% by household characteristics, and 2.7% by racial/ethnic minority status. Among all counties, poverty (incidence rate ratio [IRR], 3.2; 95% confidence interval [CI], 2.8-3.5), unemployment (IRR, 5.4; 95% CI, 4.4-6.8), lacking a high school diploma (IRR, 2.7; 95% CI, 2.4-2.9), household crowding (IRR, 3.3; 95% CI, 2.5-4.4), and lacking a vehicle (IRR, 3.4; 95% CI, 3.0-3.8) had the greatest impact on CRC mortality. Compared to urban counties, rural counties with a higher proportion of people without a vehicle had a higher risk of CRC mortality (IRR, 4.3; 95% CI, 3.7-5.0; vs. IRR, 1.9; 95% CI, 1.5-2.4).

[CONCLUSIONS] The rural-urban CRC mortality disparity is largely driven by low SES-higher poverty and unemployment, and lower income and education. The relationship between CRC mortality and the SVI is nuanced, and evaluating each component of the SVI may allow for more targeted area-level interventions than evaluating the SVI alone.