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close this bookMalaria Epidemics, Detection and Control Forecasting and Prevention (WHO - RBM - WHO - OMS, 1998, 90 p.)
close this folderIII. EPIDEMIOLOGICAL SURVEILLANCE, FORECASTING AND PREVENTION OF EPIDEMICS
close this folder9. Epidemiological Information Systems
View the document(introduction...)
View the document9.1. Identification of indicators of epidemic risk
View the document9.2. Field investigations
View the document9.3. Geographical information systems

9.3. Geographical information systems

Since epidemics are catastrophic events, their study requires the precise definition of both time and space. Both for the implementation of control interventions and for the understanding of the dynamics of risk, it is necessary to define as accurately as possible the geographical limits of each phenomenon. Most countries have good-quality topographical and political maps, showing the main physical features, the altitude, the hydrological network, the administrative boundaries, the location of villages and population centres, and national and secondary roads. They also have some form of geographical information system, providing information on agricultural areas, the distribution of main crops, irrigated areas, etc. Most of the malarious countries of the Americas and Asia made detailed geographical reconnaissances in support of the spraying operations of the malaria eradication campaigns, which in some cases provided the best available information at the time on population distribution in peripheral areas. In other countries, similar efforts have been made by other services, including the use of satellite information on surface water, vegetation and land occupation and use, of certain areas of interest to hydrological or agricultural services (Thomson et al., 1996).

Computer and communications technology provide cost-effective tools for the establishment of a dynamic information system. The existing geographical information systems (GIS) provide the programmes needed to give the required geographical dimension to epidemiological studies, and their use is spreading rapidly in most countries. Health programmes, particularly those for the elimination of dracunculiasis, the control of schistosomiasis, immunization and, in some areas, malaria control, have started to incorporate GIS in their information systems.

A computer-based GIS allows the collection of data linked to geographical location from different sources, and stores it in a form which permits subsequent analysis and synthetic presentation in map form. It is not only a system for the production of computerized maps but also, and more importantly, for the integration and spatial analysis of data from different sources such as population distribution (location of towns, villages, hamlets and road networks), the environment (physical features, land use, surface water), the location of health and other services (hospitals, dispensaries, health posts, schools, post offices, etc.), epidemiology (morbidity, mortality, drug susceptibility), meteorology (rainfall, temperature, humidity), agriculture (irrigation, main crops, land productivity), the socioeconomic situation and any other subject in which the data are linked to geographical location. Using these databases, it is possible to establish, confirm and monitor spatial and time correlations among the different data, and eventually formulate predictive hypotheses.

The study of epidemic potential should make the best possible use of any existing resources for GIS and stimulate their development where they do not exist. It is clear that GIS should be integrated in the general epidemiological services of the country. It should define the basic geographical unit of analysis of routine health data, the distribution of responsibilities for reporting, epidemiological analysis, and the communications system.

The epidemiologist responsible for malaria, whether in a specialized or an integrated service, should identify the sources of the ecological and socioeconomic data selected for monitoring. Through intersectoral collaboration, it will be necessary to ensure the automatic flow of data after agreement has been reached on the timing and points of reception as well as on their use and distribution.

The strengthening or the development of GIS for epidemic prevention and control will require financial, human and technical resources for the planning, acquisition, installation and maintenance of equipment and software, for training, supervision and evaluation, as well as for the verification, validation, correction and maintenance of related databases.