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Korean Journal of Epidemiology 1995;17(1): 94-104.
An Epidemiologic Investigation of Typhoid Fever Outbreak in 0hchun Middle and High Schools Located in Young-il Gun Kyungpook Province.
Jung Han Park, Ju Young Lee, Do Young Lee
Abstract
An epidemiologic investigation was conducted to identify the source of infection and the mode of transmission of typhoid fever outbreak occurred in Ohchun middle and high schools located in Young il Gun, Kyungpook Province from May 21 to Jun 4, 1994. Four out of 13 hospitalized students in three general hospitals in Pohang City were culture positive typhoid fever (Salmonella typhi Group D). Review of the in and outpatient logbooks of the three general hospitals in Pohang City, county health center and local clinics in the vicinity of the Ohchun middle and high schools suggested that the outbreak was confined to the schools. Drinking water source of the schools was two underground water pumps that had no treatment facilities; one in northern end and the other in southern end of the main school building. However, the southern water pump was closed on April 28, 1994 because a recent test for the water revealed E-coli suggesting a possible fecal contamination. Two hundred twenty students stated that they had experienced symptoms related to typhoid fever since April l, 1994 in a self administered questionaire survey of all of the 2, 226 students. Personal interviews with these 220 students were performed to confirm the clinical history together with a rectal swab culture for typhoid fever and Widal test. A total of 39 patients were detected; 15 confirmed cases (culture-positive) and 24 suspected cases (symptom positive with equal to or greater than 1:160 titer of Salmonella O-antibody or 1:320 titer of H-antibody titer in Widal test). The epidemic curve showed a unimodal curve with a peak on the second week(17 May, 1994) and tailed down to the 5th week (22 28 May, 1994). The overall incidence rate of typhoid fever was 1.8 per 100 students; 1.5 (1.6 for male, 1.5 for female) in the middle school and 2. 4 (6. 2 for male, 0. 4 for female) in the high school. When contrasted with the students who did not drink water at all in the school, the relative risks of incidence rate of typhoid fever for the students who drank the underground water of the school, both underground water and water brought from home, or water brought from home only were 55.5, 19.0, and 3.0 respectively. Three classes which had especially high incidence rates of typhoid fever were located in the southern part of the main school building, where the contaminated underground water pump is located. These findings suggested that the source of infection was the contaminated underground water of the school. Both of the two underground water pumps were closed permanently and the public running water was supplied to the schools.


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