Experimental use of GIS to map Chlamydia trachomatis cases to aid local intervention development

Background – Geographic information systems (GIS) are finding increasing use in mapping disease case data to assist intervention design. Theories pertaining to core transmitters and bridging populations suggest that targeting interventions to specific geographic areas can have significant results in reducing disease incidence.

Objective – The objective was to determine if the use of GIS to analyze chlamydia cases, combined with selected Census Bureau data, would be useful to a local health department (LHD) in designing an effective targeted intervention.

Methods – Five LHDs participated. All county cases for 2005 were geocoded and stratified by case count and concentration at the census block group (CBG) level. Census Bureau data concerning population demographics, education and income at the county and CBG level were collected. Maps and demographic data charts were provided to each LHD, which had ten weeks to design and implement a targeted intervention.

Results – GIS analysis showed that chlamydia does not cluster as tightly as other STDs. CBG stratification did reveal areas of high incidence or concentration that were previously unknown. LHD staff directed an intervention to target area(s) over the 10-week study period. Preliminary results suggest an insignificant impact upon local incidence.

Conclusions – All participants found the GIS data interesting, and in some cases surprising. Lack of significant impact may be due to the lack of funding, the short experimental period, and the relative mildness of infection. Furthermore, due to chlamydia's more spatially distributed nature, the use