EXPLORATORY SPACE-TIME ANALYSIS OF REPORTED DENGUE CASES DURING AN OUTBREAK IN FLORIDA, PUERTO-RICO, 1991-1992

The spatial and temporal distributions of dengue cases reported during a 1991-1992 outbreak in Florida, Puerto Rico (population = 8,689), we re studied by using a Geographic Information System. A total of 377 de ngue cases were identified from a laboratory-based dengue surveillance system and georeferenced by their residential addresses on digital zo ning and U.S. Geological Survey topographic maps. Weekly case maps wer e generated for the period between June and December 1991, when 94.2% of the dengue cases were reported. The temporal evolution of the epide mic was rapid, affecting a wide geographic area within seven weeks of the first reported cases of the season. Dengue cases were reported in 217 houses; of these 56 (25.8%) had between two and six reported cases . K-function analysis was used to characterize the spatial clustering patterns for all reported dengue cases (laboratory-positive and indete rminate) and laboratory-positive cases alone, while the Barton and Dav id and Knox tests were used to characterize spatio-temporal attributes of dengue cases reported during the 1991-1992 outbreak. For both sets of data significant case clustering was identified within individual households over short periods of time (three days or less), but in gen eral, the cases had spatial pattern characteristics much like the popu lation pattern as a whole. The rapid temporal and spatial progress of the disease within the community suggests that control measures should be applied to the entire municipality, rather than to the areas immed iately surrounding houses of reported cases. The potential for incorpo rating Geographic Information System technologies into a dengue survei llance system and the limitations of using surveillance data for spati al studies are discussed.