Spatial analysis of dengue transmission in a medium-sized city in Brazil

Abstract

OBJECTIVE: To perform spatial analysis on dengue transmission in a medium-sized city in the interior of the State of São Paulo, Brazil, covering the period from September 1990 to August 2002. METHODS: Autochthonous cases with confirmation by laboratory tests were utilized. Population data on the city of São José do Rio Preto were obtained from the Brazilian Institute for Geography and Statistics and the municipal authorities. The cases were georeferenced according to street addresses and clustered according to the 432 census tracts in the municipality, thus resulting in thematic maps. RESULTS: A rising trend in annual incidence was noted, with a peak in 2000/2001. From 1990 to 1994 the length of the transmission period reached a maximum of five months per year. This period increased in length over subsequent years. In the final year investigated, transmission occurred in all twelve months, without interruptions. Analysis of the period of highest incidence showed that the transmission did not occur uniformly. While 29% of the tracts registered incidences of less than 1,000 cases per 100,000 inhabitants, 5% of them had more than 5,000 cases. CONCLUSIONS: A process of increasing endemicity was observed, with transmission throughout the year, without the need for virus introducers. The endemic characteristic of the transmission and the differentiated occurrence according to areas need to be taken into account when developing strategies for dengue control.