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Shigellosis is an acute, infectious, inflammatory enteritis of humans. It is often clinically manifested by the dysentery syndrome(frequent bloody-mucoid stool, tenesmus, abdominal cramp). But the clinical signs and symptoms of shigellosis by S. sonnei were known as being variable and hardly defined. For this reason, There were very few studies about the case definition of shigellosis. Data mining techniques including decision tree analysis are newly developed analytical algorithms to explore the database and to discover association rules, risk factors and predictive factors. In this study, decision tree analysis technique was applied to the epidemiologic data to define the shigellosis by clinical signs and symptoms. Standard questionnaires were collected and bacteriological culture by rectal swaps were performed to all cases in two shigellosis epidemics-one for high school students and the other for elementary students. The characteristics of diarrhea were quite different from classical dysentery, and the blood -mucous type was under 5% in both group. Distributions of first symptom, maximum diarrheal number in a day and the type of diarrhea were very similar to each other groups. But the diarrheal duration of elementary students were significantly longer than those of high school students. Frequencies of abdominal cramp, headache and febrile sense were significantly high than those of high school students. As a result of decision tree analysis showed the febrile sense, maximum diarrheal number in a day, abdominal discomfort and duration of diarrhea were selected significant variables to predict the bacteriological positiveness in elementary school students. The sensitivity and specificity of this results were 51% and 97% in high school students; 91% and 79% in elementary school students respectively.
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