Information systems plays an important role in medicine because it helps process more data more efficiently while providing access to more people in different parts of the world. In this research we analyzed the data of legionella pneumophila and other legionella species collected by the public hygiene center (PHC). PHC collected 7,211 water samples from different sources of different locations in different cities in Turkey from year 1995 to 2008. The main goal of this research is to develop a conceptual framework for preventing disease and to design a medical decision support system to help administration assessing the risk of Legionnaires' disease and preventing the outbreaks of the disease. The DSS involves SOM software which was programmed with C# to search for patterns and similarities in data sets by producing SOM risk maps. Thus administrators can decide where to monitor cautiously to prevent the disease.