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The transmission of dengue fever in Puerto Rico : an epidemiologic approach using a Geographic Information System
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The transmission of dengue fever in Puerto Rico : an epidemiologic approach using a Geographic Information System
  • Corporate Authors:
    Puerto Rico. Department of Health. ; Geological Survey (U.S.) ; National Center for Infectious Diseases (U.S.)
  • Series:
    Water-resources investigations report ; 98-4119
  • Document Type:
  • Description:
    Abstract -- Introduction -- Geographic setting -- Study areas -- Methods of investigation -- Characterization of the geographic spread of dengue in the municipalities of Florida and Ponce -- Characterization of dengue case clustering patterns and Florida spatial analysis -- Movement of dengue serotypes throughout Puerto Rico -- GIS and dengue surveillance -- Summary and conclusions -- References – Glossary.

    Dengue fever, a viral disease transmitted by the mosquito Aedes aegypti, can spread rapidly in explosive epidemics. In Puerto Rico, dengue is a seasonal disease estimated to be responsible for more than 1,000 hospitalizations annually. Dengue transmission is influenced by the behavior of Aedes aegypti, movement and distribution of humans, and virus development within the mosquito. The role of each of these factors is poorly understood, in part, because of the absence of studies on the spatialtemporal patterns of dengue cases. Furthermore, recent failures of mosquito control programs designed to reduce dengue transmission indicate that long standing assumptions about the dispersal of dengue virus by mosquitoes are incorrect. The spatial and temporal distribution of dengue cases reported to the Centers for Disease Control's dengue surveillance system during a 1991-92 outbreak in Florida, Puerto Rico, and a normal transmission season (May 1994 - June 1995) in Ponce, Puerto Rico, were studied using a geographic information system. The two municipalities differed in area, population, climate, and dengue transmission intensity. Dengue cases reported in each of these municipalities were georeferenced by their residential address on Puerto Rico Planning Board digital zoning and U.S. Geological Survey topographic maps. To provide a geographic component to the existing dengue surveillance program in Puerto Rico, weekly case maps were generated for each transmission season, and then the spatial and temporal clustering patterns of the cases were described with a newly developed method called "nearest case pair analysis." For the Florida data, a sophisticated series of exploratory statistical procedures (Barton and David test, K-function analysis, Knox test) were used to describe the observed pattern of spread and case clustering. In addition, the occurrence of three individual dengue serotypes (dengue-1, dengue-2, and dengue-4) were plotted on monthly maps for the five dengue seasons (June-May) beginning in June 1989.

    The evolution of the epidemic in Florida was very rapid, affecting a large geographic area within 7 weeks of the first reported case of the season. The Barton and David test identified 23 temporal clusters of cases that had a similar spatial distribution indicating that cases were widely distributed early in the course of the epidemic. Significant dengue case clustering was identified within individual households over short periods of time (3 days or less) but, in general, the cases had spatial pattern characteristics much like the population pattern as a whole. In contrast, the progression of dengue through Ponce was characterized by the sporadic occurrence of cases for 4 months, after which dengue incidence showed a normal seasonal increase. After the seasonal increase in Ponce, the observed pattern of dengue cases was similar to that of Florida, only on a larger scale. There was less case clustering inside houses in Ponce than in Florida; only 7.3 percent of the houses in Ponce had multiple reports of dengue cases compared with 25.8 percent in Florida.

    Although clustering of dengue cases could not be identified beyond closely related cases within households, the rapid temporal and spatial progress of dengue within the community indicate that control measures should be applied simultaneously to the entire municipality, rather than in areas immediately surrounding houses of reported cases.

    At the macrogeographic level, three dengue serotypes were circulating in Puerto Rico between June 1988 and May 1994, but the relative abundance of each serotype varied with transmission season. Dengue-4 predominated in 1988, changing to dengue-2 by 1991. During the 1991-92 season, dengue-4 became very uncommon but dengue-1 reemerged and was predominant by 1993.

    The spatial analyses carried out during this project confirmed the value of geo-referencing data and the potential value of spatial statistical analyses for defining the spatial scale at which dengue surveillance, prevention, and control should be conducted. This report illustrates how medical entomologists and dengue epidemiologists can improve spatial data collection. The authors conclude that without an accurate address georeferencing system in place, incorporation of dengue case data (residential addresses of reported dengue cases reported) will do little to enhance the current dengue surveillance program in Puerto Rico.

    SuDoc number: I 19.42/4:98-4119

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