Temporal Trends in Spatial Access to Colonoscopy in South Carolina

Authors: Eberth JM, Zahnd WE, Josey MJ, Schootman M, Probst JC

Category: Cancer Health Disparities
Conference Year: 2019

Abstract Body:
Purpose: To describe temporal changes in spatial access to colonoscopy services in South Carolina (SC) between 2000 and 2014.Methods: We used data from the SC Ambulatory Surgery Database to identify the location of colonoscopy providers for each year. We estimated the annual number of adults of recommended colorectal cancer (CRC) screening age (50-74 year) in each ZIP Code tabulation area (ZCTA). The two-step floating catchment area method was used to create an annual spatial accessibility score at the ZCTA level. This method considers both supply of and demand for CRC screening within a 30-minute travel time catchment area. We used the 2003 United States Department of Agriculture Rural-Urban Commuting Area (RUCA) codes to categorize ZCTAs as rural or urban. We calculated summary statistics to describe spatial access over time and performed Wilcoxon Two-Sample Tests to compare rural-urban differences in access. Finally, we assessed spatial clustering of accessibility scores at roughly 5-year increments (2000, 2005, 2010, and 2014) by calculating Global and Local Moran’s I statistics.Results: Despite an increase over time in the number of CRC screening locations and unique providers, spatial accessibility based on the spatial accessibility score decreased 33.2% across ZCTAs from 2000 to 2014. Median spatial accessibility decreased in both urban and rural ZCTAs (25.0% and 28.5%, respectively), but spatial accessibility was significantly higher in urban ZCTAs compared to rural ZCTAs for all years (p<0.01 for each year’s comparison). The proportion of ZCTAs with no access to colonoscopy services within 30 minutes travel time increased from 15.6% in 2000 to 23.1% in 2014. Global Moran’s I statistics showed moderate spatial clustering of scores across all years assessed. Clusters of low spatial access grew in size over time and were largely situated in rural areas. Conclusions: Over time, the supply of colonoscopy services decreased relative to the potential demand for services, and clusters of low access grew over time indicating a contraction of services. Interventions should be implemented for other recommended testing modalities like fecal immunochemical testing in underserved areas in order to improve access to CRC screening.

Keywords: Colorectal cancer, screening, spatial access, GIS