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Public Health and Geographic Information Systems (GIS):  The application and analysis of disease-specific public health data from Ciudad Sandino, Nicaragua

Findings:

To date, my project has focused on upgrading the ability of the Ministry of Health officials in this municipio to record, interpret and analyze their epidemiologic health data and to gather all available reported case data on dengue and malaria for spatial analysis.

Part I of this project was accomplished by providing the health personnel at this location with a 233 MHz Pentium desktop computer with Microsoft Office 2000 and associated programs and files to maintain electronic record of the diseases of interest (See Documentation). A series of training sessions were held to provide assistance in learning how to use the computer and printer hardware and software. This instruction was provided to Dr. Rene Guiterrez, Epidemiology, Sr. Alejandro Urbina, Statistics, Sra. Maria de Jesus Zepada, Docencia, and Lic. Gregoria Monge, Epidemiology.

Part II of this in research has focused on the collection of reported case data for malaria and dengue in Ciudad Sandino. In addition, a GPS receiver was used to make a map of the entire community, including outlying disaster refugee areas established after Hurricane Mitch. Both of these components were combined to determine distribution and location of malaria and dengue within the community to add a spatial component of disease surveillance to existing techniques utilized by the community health officials. Further analysis of the disease data revealed malaria and dengue distribution within certain populations and within certain zones. In particular, malaria parasite indices were calculated by zone. Looking at the collection of data over time, the occurrences of malaria and dengue are seasonal in the community depending on the rainy season as would be expected with mosquito-vector diseases. Further, the occurrence is attributable to low lying areas and areas in close proximity to channeled waterways and ditches within the community.

Global Positioning System (GPS) and Equipment

Twenty-four satellites (21 for navigational purposes and three active reserves) orbit the Earth at approximately 10,900 miles and form the backbone of the global positioning satellite network called NAVSTAR. This system of satellites continuously broadcasts the time and orbital paths to provide the information used by a terrestrial GPS unit to compute the longitude, latitude, and altitude. Using a portable GPS device, the coordinates of any location on the planet can be recorded and tracked for navigation. For more details on how GPS works, please refer to the GPS Primer developed by the Aerospace Corporation.

Methods

A GARMIN GPS 48 hand-held device was used for this project. The GPS 48 features a 12 parallel channel receiver for fast satellite acquisition and tight satellite lock, along with a marine database that graphically displays city locations and nautical navaids on the moving map. User-selectable waypoint symbols, proximity waypoint alarms, and GARMIN's innovative TracBack^™ and Ezinit features round out this new leader in marine handheld GPS technology.  The User’s Manual was read to ensure accurate readings.  

Community Mapping

Several techniques were used to obtain accurate maps of the study area. This involved a combination of obtaining existing paper maps and validating and extending these maps into newly formed, unmapped areas using GPS-derived data. The majority of the unmapped areas are the result of Hurricane Mitch relocation efforts or expanding squatter settlement areas as a result of rural to urban migration. In reviewing the collected disease case data it was apparent that these areas were important to consider in the spatial mapping of the diseases within the community. 

The most recent community/municipal map was obtained from the local alcaldia (mayor’s office) and photocopied in Managua. An extra copy was made for the Epidemiology Department in Ciudad Sandino to update their existing community map. Further, outdated reference maps were obtained from the Department of Docencia and Statistics from the Ministry of Health in Ciudad Sandino.  These were used to locate specific houses and areas on a more resolute scale. All maps that were used were converted to digital maps using MAPSCAN developed by the United Nations Statistics Division’s Computer Software and Support for Population Activities Project.

GPS-derived mapping data was collected from taking community position fixes throughout Ciudad Sandino over a three-week period in June and July. These data points were taken at each corner block through the community in each zone and outlying areas. Points were also made of health clinics, puestos de salud, the main hospital, and other locations of significance, including the market, main catholic church and prominent markers.  Over 500 points were taken in all. Points were recorded for longititude, latitude, altitude and an error factor. This data was entered into MS Access and ArcView GIS 3.1 for creation of a point map of the community.

Malaria and Dengue/DHF Disease Case Data

All reported disease case data for malaria and dengue/DHF from Ciudad Sandino were collected from records maintained by the Department of Epidemiology and Statistics. Data collected included associated week, name, age, sex, and address of patient. Local heath officials verified this data. Addresses were correlated to the zone and manzana (city block) for spatial analysis.  Data characteristics are reviewed under the Data section. 

Spatial Distribution of Disease

A community map of Ciudad Sandino has been scanned for viewing. Various maps of the spatial distribution of disease in Ciudad Sandino have been developed using ArcView GIS 3.1. These include the distribution of malaria and dengue/DHF in Ciudad Sandino, the distribution and intensity of malaria and dengue/DHF in Ciudad Sandino. 

Conclusions

Based on initial observation of disease case plots, there is great distribution of both malaria and dengue/DHF in the zones and barrios examined. 

Further work is needed to add a variety of map features to the existing point maps. This will involve bus routes, ditches and water runoff paths, as well as a variety of additional layering of data including rainfall and climate patterns.

This is a work in progress and as my results are finished, they will be added. Thanks for your patience.

The content of the page is produced by John M. Miller and any and all comments, question, or suggestions should be addressed to me. 

Last Updated October 25, 2000