Geographic Epidemiology of Gonorrhea in Baltimore, Maryland, Using a

The epidemiology of gonorrhea is characterized by geographically defined hyperendemic areas, or "cores." Geographic information system (GIS) technology offers new opportunities to evaluate these patterns. The authors developed a GIS system linked to the disease surveillance database at the Baltimore Health Depart-ment and used this system to evaluate the geographic epidemiology of gonorrhea in Baltimore, Maryland, during 1994. There were 7,330 reported cases, of which 87.4 % were in persons 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 geocoded by reported address using digitized maps, and assigned to census tract. Census tract-specific rates for persons aged 15-39 years were calculated using 1990 census data. Gonorrhea was reported from 196/202 (97%) of census tracts, of which 90 census tracts had>30 cases. For these 90 census tracts, rates were ranked. The core was considered as the top rate quartile, consisting of 13 geographically contiguous census tracts with rates 4,370-6,370 per 100,000; adjacent areas were 19 census tracts in the second quartile (rates: 3,730-4,370 per 100,000). As radial distance from the core areas increased, incidence rates decreased and male/female ratio increased, which is consistent with previous definitions of the core theory of STD transmission. Mapping of cases by provider showed that cases reported from STD clinic