Background:
Identification of sexually transmitted infection (STI) clusters has been helpful in understanding transmission dynamics and targeting resources.

Objective:
Use geographic information systems (GIS) and spatial statistics to identify major geographic STI clusters in Connecticut (CT).

Method:
Persons with chlamydia and gonorrhea infections reported to the Connecticut Department of Public Health (CDPH) during 2004 were divided into five groups, (1) single diagnosis of chlamydia; (2) single diagnosis of gonorrhea; (3) repeat chlamydia diagnoses; (4) repeat gonorrhea diagnoses; and (5) simultaneous diagnoses of chlamydia and gonorrhea. Affected persons were geocoded on the basis of their reported home address. A statistically significant cluster was defined as one or more census tracts with a higher than expected rate of infection for each defined group (P < .05). A scan statistic based on the Poisson model was used to identify the most likely cluster and determine its statistical significance.

Result:
A total of 9,595 chlamydia infections and 2,891 gonorrhea infections were reported to CDPH during 2004. Ultimately, 8,584 persons with 9,912 infections were geocoded; this represented ~80% of all infections reported. A significant cluster was identified for all five groups. The number of census tracts involved in each cluster ranged from 39 to 49. Four of the five groups, including the simultaneous diagnoses group, had a cluster identified in the same geographic area of the state.

Conclusion:
Statistically significant geographic clusters for chlamydia and gonorrhea exist in CT. Persons with simultaneous infections might represent a core group in STI transmission.

Implications:
Consideration should be made to target available STI resources to cluster areas in CT. Persons diagnosed with simultaneous chlamydia and gonorrhea infections should be studied further as a potential core group of STI transmission.