Background:
Many Illinois counties sustain a chlamydia incidence rate significantly higher than the state average. Current intervention policy is based upon state-provided testing coupled with local health department (LHD)-developed interventions. Many LHD staff lack the training and resources to implement innovative interventions.

Objective:
The objective was to determine if a policy of state health department assistance in the development of a geographic information system (GIS)-based targeted intervention at the local level would be cost-effective.

Method:
County chlamydia cases for 2005 were geocoded and stratified at the census block group (CBG) level. Census Bureau data at the county and CBG level were collected, and maps and demographic data charts were provided to each LHD. Participants had ten weeks to implement an intervention to targeted areas.

Result:
LHD staff completed their interventions during the study period. Resultant incidence was examined by ARIMA time series modeling, chi-square analysis and t-tests. No case counties experienced a significant decrease. However, analysis showed that an annual decrease of < 2.0% is sufficient to make all tested interventions cost-effective for most values of disease progression and estimated costs.

Conclusion:
All participants found the data useful in developing a targeted intervention. The large variance in monthly county case counts contributed to wide confidence intervals for predicted values. Incidence decreases which would be cost-effective might be too small to be seen. The lack of supplemental funding, the short experimental period, and the relative mildness of infection likely limited intervention extent and effectiveness.

Implications:
The use of GIS may be a cost-effective complement to traditional intervention strategies. The state health department can provide direction and data LHDs are unable to acquire on their own. Allowing GIS activities in the CDC grant to the states may make significant impacts in state/local incidence as well as strengthen state and local collaborative relationships.