Does core area theory apply to sexually transmitted diseases in rural environments?

Abstract

Background: Our objective was to determine the extent to which geographical core areas for gonorrhea and syphilis are located in rural areas as compared with urban areas.

Methods: Incident gonorrhea (January 1, 2005-December 31, 2010) and syphilis (January 1, 1999-December 31, 2010) rates were estimated and mapped by census tract and quarter. Rurality was measured using percent rural and rural-urban commuting area (rural, small town, micropolitan, or urban). SaTScan was used to identify spatiotemporal clusters of significantly elevated rates of infection. Clusters lasting 5 years or longer were considered core areas; clusters of shorter duration were considered outbreaks. Clusters were overlaid on maps of rurality and qualitatively assessed for correlation.

Results: Twenty gonorrhea core areas were identified: 65% were in urban centers, 25% were in micropolitan areas, and the remaining 10% were geographically large capturing combinations of urban, micropolitan, small town, and rural environments. Ten syphilis core areas were identified with 80% in urban centers and 20% capturing 2 or more rural-urban commuting areas. All 10 (100%) of the syphilis core areas overlapped with gonorrhea core areas.

Conclusions: Gonorrhea and syphilis rates were high for rural parts of North Carolina; however, no core areas were identified exclusively for small towns or rural areas. The main pathway of rural sexually transmitted disease (STI) transmission may be through the interconnectedness of urban, micropolitan, small town, and rural areas. Directly addressing STIs in urban and micropolitan communities may also indirectly help address STI rates in rural and small town communities.

Figure 1

North Carolina a) rurality defined using rural-urban commuting areas (RUCAs), b) average gonorrhea rates (January 1, 2005 to December 31, 2010) and c) syphilis rates (January 1, 1999 to December 31, 2010) by census tract.

Figure 2

Significant clusters of high A) gonorrhea rates (2005 to 2010) and B) syphilis rates for North Carolina (1999 to 2010) overlaid on rural urban commuting areas (RUCAs).

Figure 3

Gonorrhea (2005-2010) and syphilis (1999-2010) clusters overlaid with each other, RUCA (A), and percent rural (B).

Figure 4

A) Gonorrhea (top row) and B) Syphilis (bottom row) clusters detected when North Carolina is stratified into Mountain, Piedmont and Coastal socio-geographic regions.