OBJECTIVES: This paper was undertaken to explore the relationship of a 4-year period dengue incidence and the interplay of selected spatial factors (i.e., build-up structures, existing land use/cover types, and presence of water networks) in Quezon City, Philippines. It attempts to examine why dengue incidences are higher in some areas, looking at factors such as geographical attributes, livelihood activities, and practices in the area. At the end of this paper, dengue risk maps will be produced to guide local health authorities target specific areas for focused interventions to manage future dengue outbreak in the area.

METHODS: Reports on dengue cases over the 4-year period (2005-2008) from the City's Health Department Office were encoded and exported in ArcGIS 9.1, a Geographic Information Systems (GIS) mapping software technology. Together with the city's environmental conditions, dengue frequencies were mapped out, overlaid, and examined to determine whether or not these environmental factors affect, contribute and link to the dengue occurrence in an area.

RESULTS: After rendering the dengue risk maps, the highest frequency of dengue is evident in the eastern portion of Quezon City covering District II. Overlaying or superimposing dengue frequency layers with the spatial factors being considered in this study has revealed that these factors affect and contribute to the occurrence of dengue in an area. Areas with a number of river networks and built-up structures experience high dengue incidence. Lands used for residential purposes with neighboring commercial/industrial structures also tend to be dengue susceptible. However, the population density factor alone does not necessarily translate to high dengue frequency. Barangays (the smallest administrative divisions of the city) with high recorded dengue frequency are areas within or near dumpsite facilities primarily because of sanitation concerns as well as the type of livelihood and inherent practices of majority of the residents.

CONCLUSIONS: This research provides an understanding of the spatial epidemiology of dengue in Quezon City using GIS as a tool for identifying high risk areas for dengue. Spatial examination has been carried out to determine spatial anomalies (high concentration of incidence) and the spatial makeup of the area that affects or contributes to such anomalies. The role of GIS in public health decision-making is evident in identifying high risk areas and creating dengue risk maps. Local health authorities will be in a better position to target priority areas and decide where to put scarce resources for programs and projects that will address further disease outbreaks.