Objective Chlamydia, gonorrhoea and syphilis (primary and secondary) are at high levels in the USA. Disparities by race, gender and sexual orientation have been characterised, but while there are indications that rural poor populations may also be at distinct risk this has been subjected to little study by comparison. The federally designated Delta Regional Authority, similar in structure to the Appalachian Regional Commission, oversees 252 counties within eight Mississippi Delta states experiencing chronic economic and health disparities. Our objective was to identify differences in infection risk between Delta Region (DR)/non-DR counties and examine how they might vary by rurality, population density, primary care access and education attainment.

Methods Reported chlamydia/gonorrhoea/syphilis data were obtained from the Centers for Disease Control and Prevention AtlasPlus, county demographic data from the Area Health Resource File and rurality classifications from the Department of Agriculture. Data were subjected to analysis by t-test, χ² and linear regression to assess geographical disparities in incidence and their association with measures of rurality, population and primary care density, and education.

Results Overall rates for each infection were significantly higher in DR versus non-DR counties (577.8 vs 330.1/100 000 for chlamydia; 142.8 vs 61.8 for gonorrhoea; 3.6 vs 1.7 for syphilis; all P<0.001) and for nearly every infection for every individual state. DR rates for each infection were near-universally significantly increased for every level of rurality (nine levels) and population density (quintiles). Regression found that primary care and population density and HS graduation rates were significantly associated with each, though model predictive abilities were poor.

Conclusions The nearly 10 million people living in the DR face significant disparities in the incidence of chlamydia, gonorrhoea and syphilis—in many instances a near-doubling of risk. Our findings suggest that resource-constrained areas, as measured by rurality, should be considered a priority for future intervention efforts.