GEOGRAPHIC EPIDEMIOLOGY OF GONORRHEA IN BALTIMORE, MARYLAND, USING A GEOGRAPHIC INFORMATION-SYSTEM

The epidemiology of gonorrhea is characterized by geographically defin ed hyperendemic areas, or ''cores.'' Geographic information system (GI S) technology offers new opportunities to evaluate these patterns. The authors developed a GIS system linked to the disease surveillance dat abase at the Baltimore Health Department and used this system to evalu ate the geographic epidemiology of gonorrhea in Baltimore, Maryland, d uring 1994. There were 7,330 reported cases, of which 87.4% were in pe rsons aged 15-39 years; 56.6% were of the cases were in males; and 60. 5% of the cases were reported from the nonsexually transmitted disease (STD) clinic sector, Valid residential addresses were available for 6 ,831 (93.5%) of cases. In the GIS system, gonorrhea cases were geocode d by reported address using digitized maps, and assigned to census tra ct, Census tract-specific rates for persons aged 15-39 years were calc ulated using 1990 census data. Gonorrhea was reported from 196/202 (97 %) of census tracts, of which 90 census tracts had >30 cases. For thes e 90 census tracts, rates were ranked. The core was considered as the top rate quartile, consisting of 13 geographically contiguous census t racts with rates 4,370-6,370 per 100,000; adjacent areas were 19 censu s tracts in the second quartile (rates: 3,730-4,370 per 100,000). As r adial distance from the core areas increased, incidence rates decrease d and male/female ratio increased, which is consistent with previous d efinitions of the core theory of STD transmission, Mapping of cases by provider showed that cases reported from STD clinics had similar geog raphic distribution to those from the non-STD clinic sector. From an o perational perspective, GIS can be effectively integrated with clinica l data systems to provide epidemiologic analysis.