Spatial and temporal dynamics of dengue haemorrhagic fever epidemics, Nakhon Pathom province, Thailand, 1997-2001

Abstract

Several environmental factors modulate the distribution of dengue fever (DF), such as climate, density of vector and human populations in urban areas and distribution of herd immunity. In order to identify geographical variables involved in the spread of a DHF process, a Geographic Information System (GIS) has been built to create links between geo-referenced data including medical records and socioeconomic and environmental data. Applied to a retrospective analytical study of DHF epidemics in Nakhon Pathom province (1997-2001), the GIS allowed a mapping of spatial variations of DHF incidence, the recognition of different temporal incidence patterns and the quantification of the dispersal of outbreaks among defined spatial units. The analysis showed that the diffusion process of these epidemics was of a contagious type as the distance between epidemic areas (sub-districts) was significantly lower than the average distance between every sub-district. This result indicates that these epidemics were likely to be due to the spread of a new or rare virus serotype, from its emergence location in the province to areas with a sufficient density of vectors and a similar limited immune protection against this serotype.