Spatial accessibility to colonoscopy and its role in predicting late-stage colorectal cancer

Abstract

Objective: To better determine the relationship between spatial access to colonoscopy and colorectal cancer (CRC) outcomes, our objective was to examine the agreement of the classic, enhanced, and variable two-step floating catchment area (2SFCA) methods in evaluating spatial access to colonoscopy and to compare the predictive validity of each method related to late-stage CRC. 2SFCA methods simultaneously consider supply/demand of services and impedance (ie, travel time).

Data sources: Colonoscopy provider locations were obtained from the South Carolina Ambulatory Surgery Database. ZIP code tabulation area (ZCTA) level population estimates and area-level poverty level were obtained from the American Community Survey. Rurality was determined by the United States Department of Agriculture's Rural-Urban Commuting Area codes. Individual-level CRC data were obtained from the South Carolina Central Cancer Registry.

Study design: Using the classic, enhanced, and variable 2SFCA methods, we calculated ZCTA-level spatial access to colonoscopy. We assessed agreement between the three methods by calculating Spearman's rank coefficients and weighted Kappas (Κ). Global and Local Moran's I were used to assess spatial clustering of accessibility scores across 2SFCA methods. We performed multilevel logistic regression analyses to examine the association between spatial accessibility to colonoscopy, area- and individual-level factors, and late-stage CRC.

Principal findings: We found strong agreement (Weighted Κ = 0.82; 95% CI = 0.79-0.86) and identified similar clustering patterns with the classic and enhanced 2SFCA methods. There was negligible agreement among the classic/enhanced 2SFCA and the variable 2SFCA. Across all 2SFCA methods, regression models showed that spatial access to colonoscopy, rurality, and poverty level were not associated with greater odds of late-stage CRC, though Black race was associated with late-stage CRC across all models.

Conclusions: None of the 2SFCA methods showed an association with late-stage CRC. Future studies should explore which elements (spatial or nonspatial) of access to care have the greatest impact on CRC outcomes.

Keywords: GIS; colonoscopy; colorectal cancer; spatial accessibility; two-step floating catchment area method.

FIGURE 1

Distribution of Scores (Quartiles) by ZCTA: A, 2SFCA; B, E2SFCA; C, V2SFCA. Abbreviations: 2SFCA, two‐step floating catchment area; E2FCA, enhanced two‐step floating catchment area; V2SFCA, variable two‐step floating catchment area [Color figure can be viewed at wileyonlinelibrary.com]

FIGURE 2

Spatial Patterns in Spatial Accessibility Scores A, 2SFCA; B, E2SFCA; C, V2SFCA. Abbreviations: 2SFCA, two‐step floating catchment area; E2FCA, enhanced two‐step floating catchment area; V2SFCA, variable two‐step floating catchment area [Color figure can be viewed at wileyonlinelibrary.com]