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Sexually transmitted infections in the Delta Regional Authority: significant disparities in the 252 counties of the eight-state Delta Region Authority
  1. Alexandra C Barger1,
  2. William S Pearson2,
  3. Christofer Rodriguez3,
  4. David Crumly3,
  5. Georgia Mueller-Luckey4,
  6. Wiley D Jenkins
  1. 1 Medical Student, Southern Illinois Univeristy School of Medicine, Springfield, Illinois, USA
  2. 2 Division of STD Prevention, Centers for Disease Control and Prevention, Atlanta, Georgia
  3. 3 Population Science Research Specialist, Office of Population Science and Policy, Southern Illinois University School of Medicine, Springfield, Illinois, USA
  4. 4 Department of Applied Health, Southern Illinois University Edwardsville, Edwardsville, Illinois, USA
  1. Correspondence to Dr Wiley D Jenkins, Office of Population Scienceand Policy, Southern Illinois University School of Medicine, Springfield, IL 62702, USA; wjenkins{at}


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.

  • sexually transmitted diseases
  • health status disparities
  • chlamydia trachomatis
  • neisseria gonorrhoeae
  • syphilis
  • Delta Regional Authority
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Chlamydia trachomatis and Neisseria gonorrhoeae are the two most commonly reported bacterial infections in USA.1 Along with Treponema pallidum infection, causing primary and secondary syphilis, there are nearly two million cases of these STIs reported annually(see online supplementary table 1 for the current STD rates for the eight Delta Region (DR) states). These STIs lead to high levels of morbidity among certain populations and contribute to increased healthcare expenditures.2 These infections have reached record reported levels for the past several years, syphilis especially increasing in incidence (eg, 17.6%, 2015–2016).3 4 All three infections are amenable to screening, but such interventions are suboptimally used and more accessible in metropolitan areas.5 The substantial morbidity associated with untreated infection (eg, pelvic inflammatory disease, ectopic pregnancy, chronic pelvic pain and facilitated HIV transmission) and increasing concern regarding antimicrobial-resistant gonorrhoea, fuel a need to consider STI epidemiology in additional ways.6 7

To begin with, these STIs are not necessarily an ‘urban’ problem, with a few studies indicating disparately high rates among at least some rural populations.8–10 Further, rural adolescents may be more likely than their urban peers to engage in risky sexual activities (eg, vaginal sex without a condom, alcohol during last sex).11 12 Recent work also finds that rural men who have sex with men are more likely to report facing intolerance, and less likely to use basic HIV prevention services, than their urban peers.13 Addressing this adequately is problematic as many rural local health departments (LHDs) lack standardised data collection (limiting critical demographic information such as race and income), and time and resources for prevention and education.14 Overall, rural LHDs have been described as facing a ‘double disparity’ consisting of a service population experiencing disproportionately high rates of risky health behaviours coupled with historically low funding and investment.15

Still, identifying the nearly 20% of the US population residing in rural areas as being of perhaps increased STD risk but with less access to prevention and care as a population at risk is not necessarily specific enough for targeted resources and intervention.16 Further, this would assume that all ‘rural’ is homogeneous in risk when studies in other disciplines (eg, cancer epidemiology) have found that to be false.17 18 Further refinement may come from concurrent consideration of both geography (with recent geospatial studies indicating clustering of some STIs in the American South and along the Mississippi River) and population demographics (where poverty/low income and various racial/ethnic community compositions are often associated with STI risk).2 19–21 Many of these factors coalesce in the Delta Regional Authority; a federally designated region of 252 counties and parishes in eight states along the Mississippi River and the Alabama Black Belt (illustrated in online supplementary figure 1A–C by a blue outline).22 In this region, 1 in 5 of the nearly 10million residents lives in poverty, compared with 14.9% nationwide, and nearly half of the counties have been designated as persistent poverty counties.23 Federally designated in 2000, this region faces exceptionally high rates of poverty, lower average level educational attainment and known health disparities (eg, cancer).24

In spite of data indicating potential increased STI risk in rural poor populations, the smaller numbers of cases and low population density typical of rural counties has resulted in little research conducted on this topic. Thus, little is known regarding STI risk in the DR as opposed to non-DR areas within the same states. Identifying and describing adverse health outcomes in this federally designated region may support arguments for greater investment in healthcare access and policy.

Materials and methods

All 719 counties contained within the eight DR states (Alabama, Arkansas, Illinois, Kentucky, Louisiana, Mississippi, Missouri and Tennessee) were classified as either belonging to the DR (DR counties) or not (non-DR).23 County-level STI rates (2010–2014) were obtained from the National Centre for HIV/AIDS, Viral Hepatitis, STD and TB Prevention AtlasPlus data set.25 Rural-Urban Continuum Codes (RUCCs) were used to assess levels of rurality, which are categorised as follows26:

  1. Metro—Counties in metro areas of 1million population or more

  2. Metro—Counties in metro areas of 250 000to1million population

  3. Metro—Counties in metro areas of fewer than 250 000 population

  4. Non-metro—Urban population of 20 000 or more, adjacent to a metro area

  5. Non-metro—Urban population of 20 000 or more, not adjacent to a metro area

  6. Non-metro—Urban population of 2500to19 999, adjacent to a metro area

  7. Non-metro—Urban population of 2500to19 999, not adjacent to a metro area

  8. Non-metro—Completely rural or less than 2500 urban population, adjacent to a metro area

  9. Non-metro—Completely rural or less than 2500 urban population, not adjacent to a metro area

Area Health Resource Files provided data regarding county population density characteristics, primary care provider density (PCP) and high school graduation rates (HS).27 Population density at the county level was stratified into five levels with each containing approximately 20% of total counties.

T-tests compared rates of chlamydia, gonorrhoea, and primary and secondary syphilis for the entire DR (DR x non-DR counties) and stratified by state. Analysis of variance compared STI rates in relation to categorised rurality (RUCC) and stratified population density. Regression analysis used primary care and population density (continuous) and HS to predict each STI. Poisson regression analysis with a Pearson Scale correction for overdispersion was used to explore unadjusted and adjusted chlamydia, gonorrhoea and syphilis rates between DR and non-DR counties. Model adjustments included population density, RUCC, HS, PCP and race. Population and primary care density were standardised for regression analyses and interpreted as the distance from the mean. All analyses were performed in SPSS V.24.


Of the 719 counties across the eight DR states, 252 were DR and 467 were non-DR. Overall, DR counties had significantly higher rates of chlamydia (577.8 vs 330.1/100 000), gonorrhoea (142.8 vs 61.8) and syphilis (3.6 vs 1.7; all P<0.001; table 1) infection. Many of these disparities remained after stratifying by individual state (eg, DR vs non-DR chlamydia in Tennessee at 528.4 vs 264.9/100 000). A spatial representation of county STI rates in relation to each state’s overall rate is shown in the online supplementary figure 1. HS in non-DR counties exceed that for DR overall and for individual states (except Arkansas), but PCP is not significantly different overall or for individual states (except Louisiana). Finally, all three STIs are positively correlated with each other (all P<0.001) while each is negatively correlated with both HS and PCP (all P<0.001; table 2).

Table 1

Reported STI and high school graduation rates (HS) and primary care physician density (PCP) in Delta Region (DR) versus non-Delta Region (non-DR) counties, 2010–2014, stratified by state

Table 2

Correlations between STI and high school graduation rates and primary care physician density across the entire Delta Region

Examining STI rates by rurality, chlamydia and gonorrhoea are significantly higher in DR vs non-DR counties for each RUCC level (table 3) and with syphilis similarly significantly increased except among RUCC 5 counties. A similar examination using population density found that DR STI rates significantly exceeded non-DR for each infection for all levels. Unadjusted univariate regression analysis found that primary care availability, population density and HS were all significantly associated with each STI (all P<0.001) though model predictions were modest (R2 ranging from 0.078to0.237). Individual state models were also all significant for each STI, though not all variables retained significance for each STI/state (data not shown). Poisson regression models found increased rates for each STI DR versus non-DR, with the incidence rate ratio for chlamydia at 1.4 (CI 1.35 to 1.45; P<0.001), gonorrhoea at 1.55 (CI 1.46 to 1.63; P<0.0001) and syphilis at 1.30 (CI 1.18 to 1.43; P<0.0001). This difference remained after adjusting for population density, RUCC, HS, population per PCP and race (P<0.0001; table 4).

Table 3

Comparison of DR vs non-DR STI rates, Stratified by rurality and population Density—2010–2014 data only

Table 4

Regression Analysis of STI rates between Delta Region (DR) and non-DR counties


The results show disparities in STI rates among DR counties versus non-DR counties. The overall rate of chlamydia is approximately 75% higher among DR counties, while gonorrhoea and syphilis are 131% and 112% higher, respectively. These significantly increased rates are maintained for nearly all STIs in individual states (with chlamydia in Missouri and syphilis in Kentucky the sole exceptions). HS and PCP are both negatively associated with STI rates among both DR and non-DR counties. PCP only significantly varies in Louisiana between DR and non-DR counties, and while HS is lower in DR counties for all states (except Arkansas), the difference is for the most part in the 2%–3%range. DR counties are more rural than non-DR (72.2% of them classified as RUCC 4–9 compared with only 60.8% of non-DR counties) and generally of lower population density (72.6% in population density groups 3–5 compared with 53.3% of non-DR). An interesting finding is that the STI disparities are found at every level of rurality and density (syphilis in RUCC 5 being the sole exception).

DR counties experienced significantly higher rates of chlamydia, gonorrhoea and early syphilis infection than their non-DR counterparts in the same states, and this difference is consistent for essentially all levels of rurality and population density. From 2012 to 2014, the DR appeared to have higher rates per 100 000 population of chlamydia and gonorrhoea, but not of syphilis, compared with USA as a whole. We believe that further data are required to identify areas where resources are lacking and interventions are needed in order to better direct and generate hypotheses regarding STI epidemiology in large-scale rural and impoverished areas.

Screening of at-risk individuals is a primary means of intervention for STI infection and transmission, and previous work has shown that the majority of STI identification and treatment takes place in clinical venues, which are not always traditional STD clinics.1 23 28 However, these prevention programmes are resource-dependent and may be less accessible for individuals living in more resource-poor rural areas.29 30 The pervasive increased STI risk among the largely rural and poor DR counties provides yet another argument for increased access to medical care in these areas. A complementary approach might include increasing the resources of the approximately 2800 LHDs located across USA. Such departments in rural communities currently face increased barriers to the suite of STI services addressing screening, reporting and prevention/education.31 32 Other safety net screening venues, such as school-based clinics and STI clinics, are typically located in areas with greater resources and population density and may be less feasible to expand in less populated areas.14 33


Our analysis of the DR indicates that there may exist large rural populations of increased STI risk. The disparities seen in urban versus rural non-DR regions may hold for other urban versus rural areas as well. Because clinical diagnosis relies on available and accessible screening services, there may be an unappreciated burden of STIs in other rural areas. Further investigation is needed to determine what DR characteristics are leading this area to experience higher STI rates, and what interventions might be most appropriate for rural populations.

Key messages

  • Rural areas are infrequently studied for STI risk though they comprise 20% of the US population and may contribute to ever-increasing reported rates.

  • Many rural areas experience factors associated with increased risk of STI, such as low income, increased alcohol use and increased risky sexual behaviours.

  • Our analysis of STI in the federally designated and largely rural Delta Region found significantly and consistently increased rates of chlamydia, gonorrhoea and syphilis.

  • Identification of increased risk within this population may direct further research into specific causal factors, and justify intervention resources towards a distinctly identified group.


View Abstract


  • Handling editor Jackie A Cassell

  • Funding This research did not receive any specific grant from any funding agencies in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient consent Not required.

  • Ethics approval Ethical approval was not required for this study because the data being used are publicly available.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data sharing statement Data used for this study were obtained from publicly available information from the following three organizations: (1) The Centers for Disease Control and Prevention, (2) Area Health Resource Files from the Health Services Resource Administration, (3) The US Department of Agriculture.

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