GIS model essential for identifying high risk areas for dengue

Dengue, a vector-borne disease, is considered one of the most dreaded health problems worldwide. In the report published by the World Health Organization (WHO), dengue epidemic is now becoming widespread in more than 100 countries in Africa, America, Eastern Mediterranean, Southeast Asia and the Western Pacific, affecting more than 2,500 million people or about two-fifth’s of the world population.

In the Philippines, 70, 000 dengue cases were reported from January to September this year. Though it is 25 percent lower compared to the cases of the same period last year, the government vows to intensify its campaign against dengue.

Aside from the nationwide distribution of the Ovicidal Larvicidal (OL) trap technology, the government is exploring other possible interventions such as the use of the geographic information system (GIS).

A recent study by Prof. Fernando Garcia from the College of Public Health, University of the Philippines Manila (UPM), An Examination of the Spatial Factors of Dengue Cases in Quezon City, A Geographic Information-Based Approach, showed that GIS can help the government in the quick identification of dengue high risk areas.

“In order to effectively control the dengue disease, it is important to understand the vector – the Aedes mosquitoes and the contributing factors that influence its occurrence and reoccurrence,” said Prof. Garcia.

In the study, environmental factors such as build-up structures, existing land use or cover types, and presence of water networks were assessed in relation to the occurrence of dengue incidence in Quezon City.

2005-2008 data on dengue incidence from the Quezon City Health Office were used as reference. Together with identified environmental factors, the dengue frequencies were mapped, overlaid, and analyzed.

Results of the study showed that the highest frequency of dengue is evident in the eastern portion of Quezon City, covering the Barangays of Matandang Balara, Batasan Hills, Commonwealth and Payatas. Dengue frequencies in these areas were consistently high throughout the four -year period of data. “These are the adjacent areas within the La Mesa Dam Reservoir – part of the river basins of the neighbouring cities and localities such as San Juan Pasig, Marikina, Tullahan, Tenejeros, and Meycauayan, Bulacan.”

On the other hand, population density is not significant to dengue occurrence. Based on the data gathered, both high densely populated (Barangay Bagong Pag-asa and Tatalon) and low densely populated areas (Barangay Batasan Hills, Holy Spirit, Payatas, Commonwealth, Matandang Balara and Bahay Toro) in Quezon City recorded high dengue incidence. “In fact, many areas with high dengue incidence were low densely populated barangays,” added Prof. Garcia.

The study also examined why dengue incidences are higher in some areas, taking into consideration other factors such as geographical attributes, livelihood activities, and hygiene practices in the community. “For example, poor sanitary practices of people, especially those living near dumpsites, may contribute to high occurrence of dengue and other occupational diseases such as parasitic, enteric and viral infections,” said Prof. Garcia.

Incidence of dengue is also higher in areas where there are Soil Organic Carbon (SOC). These are areas where diverse combination of materials such as plants, animals, and other decaying materials are stored. “It maybe in these locations where segregation of waste materials is not properly done, leaving behind solid waste materials such as containers with decaying materials. This makes it more conducive for dengue mosquitoes to lay their eggs,” said Prof. Garcia.

“With GIS, we can create dengue risk maps essential in the formulation of evidence -based decisions. Local 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,” Prof. Garcia concluded.