Using GIS to Evaluate Utilization of Sexually Transmitted Diseases (STD) Services in a Northern California County with Substantial HIV Late Presentation

Background:
San Mateo County (SM) has a higher prevalence of HIV late presentation (62%) than neighboring counties (San Francisco (SF) 39%) and the national average (43%). SM's syphilis rate tripled in 2006 (4.5 cases per 100,000) compared to 2005. Half of these cases were HIV infected. We sought to evaluate utilization of STD services for persons living in the highest STD morbidity areas to the SM STD clinic and neighboring county STD services (SF and Santa Clara (SC)).

Objective:
To evaluate use of SM STD clinic and neighboring county STD services by persons living in highest SM STD morbidity zip code areas.

Method:
Residential information on all SM residents who visited one of the three County Bay Area STD Clinics (SM, SF and SC Clinics) in 2006 were mapped using ArcGIS 9.1 by zip code. These data were compared with all confirmed STD cases reported to the Health Department in 2006.

Result:
SM STD clinic had 2,109 visits in 2006. The majority of SM STD visits were from mid (38%) and south-county areas (26%), which are geographically closest to the clinic. SF Clinic reported 1,219 visits from SM residents; more than 50% of all visits to SM STD in 2006. 54% of SF visits were from the north-county, where 28% of all confirmed STD cases in SM reside.

Conclusion:
Inter-jurisdictional use of STD services in Northern California is common. Northern SM has both high STD morbidity and significant use of SF STD services.

Implications:
Given the shared clinical populations in Northern California, approaches that are inter-jurisdictional may have largest impact. The importance of inter-county sexual networks for men who have sex with men in the region should be evaluated.