BACKGROUND

Although colorectal cancer death rates in the United States have declined by half since 1970, large geographic disparities persist. Spatial identification of high-risk areas can facilitate targeted screening interventions to close this gap.

METHODS

We used the Getis-Ord Gi* statistic within ArcGIS to identify contemporary colorectal cancer "hotspots" (spatial clusters of counties with high rates) based on county-level mortality data from the national vital statistics system. Hotspots were compared with the remaining aggregated counties (non-hotspot United States) by plotting trends from 1970 to 2011 and calculating rate ratios (RR). Trends were quantified using joinpoint regression.

RESULTS

Spatial mapping identified three distinct hotspots in the contemporary United States where colorectal cancer death rates were elevated. The highest rates were in the largest hotspot, which encompassed 94 counties in the Lower Mississippi Delta [Arkansas (17), Illinois (16), Kentucky (3), Louisiana (6), Mississippi (27), Missouri (15), and Tennessee (10)]. During 2009 to 2011, rates here were 40% higher than the non-hotspot United States [RR, 1.40; 95% confidence interval (CI), 1.34-1.46], despite being 18% lower during 1970 to 1972 (RR, 0.82; 95% CI, 0.78-0.86). The elevated risk was similar in blacks and whites. Notably, rates among black men in the Delta increased steadily by 3.5% per year from 1970 to 1990, and have since remained unchanged. Rates in hotspots in west central Appalachia and eastern Virginia/North Carolina were 18% and 9% higher, respectively, than the non-hotspot United States during 2009 to 2011.

CONCLUSIONS

Advanced spatial analysis revealed large pockets of the United States with excessive colorectal cancer death rates.

IMPACT

These well-defined areas warrant prioritized screening intervention.