Spatial patterns of diarrhoeal illnesses with regard to water supply structures--a GIS analysis

This paper presents an application of a geographical information system (GIS) in the field of research of drinking water epidemiology. A retrospective study regarding gastrointestinal infections was carried out in the Rhine-Berg District (North Rhine-Westphalia, Germany), which is characterised by different drinking water supply structures. The main objective was to examine the hypothesis that spatial variations of diarrhoeal illnesses may be linked with different drinking water sources (groundwater or surface water). We introduced a GIS for storing and analysing the wide range of data sets comprising features of the water supply structure and the epidemiological databases which constitute the basic elements of a surveillance-system for waterborne infectious diseases. GIS-techniques supported the generation of hypotheses regarding disease distribution and causation. The data bases which are routinely available turned out to be of sufficient quantity and quality for running a waterborne disease surveillance-system. Geo-statistical analysis revealed spatial variations in the incidence of diarrhoeal illnesses. Parameters depicting the water supply structures, especially the amount of drinking water produced from surface or groundwater, were correlated with the age-standardised incidence rates of gastrointestinal infections. The correlation models showed a trend of positive linkage between disease incidence and amount of groundwater. We found GIS-techniques extremely useful to carry out area-based correlation studies and to analyse the exposure of populations in drinking water epidemiology.