The dot map as an epidemiological tool: a case study of Schistosoma mansoni infection in an urban setting.

In this paper dot maps are used as an epidemiological tool to describe the spatial patterns of cases, non-cases and some relevant risk factors associated with the occurrence of Schistosoma mansoni infection in an urban environment. The study was carried out in Santo Antonio de Jesus, a town in north-east Brazil with a population of around 45,000 inhabitants. The survey was targeted at all children aged between 12 years 8 months and 14 years 11 months who were living in the town at the time of the survey. An extensive questionnaire was used to collect information on each child and on family and household conditions; stool samples were also taken for quantitative examination. A computerized digitizer was used on a map (scale 1:4000) to create x and y coordinates for each child's household. The result was matched with individual data from the questionnaires and the stool examination. From this data base it was possible, by using a statistical package, to make epidemiological analyses and by using the statistical package associated with a geocartographic system package it was possible to dot plot selected values of defined variables. These techniques substantiated the findings on the risk factors at a local level and, as a consequence, improve our ability to define targeted actions towards local control of schistosomiasis.