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Korean Journal of Epidemiology 1992;14(1): 91-101.
Published online Jun 30, 1992.
An Epidemiologic Study on the Leptospiral Infection in the Period of an Anticipated Epidemic
Bo Youl Choi1, Dae Eun Chung1, Soo Jin Lee1, Hung-Bae Park1, Jeoung Bae Park2, Kyung Hee Lee2, Jeong Soon Kim3
1Department of Preventive Medicine, Hanyang University
2Army Sergeon, Captain
3School of public Health, Seoul National University
Abstract
A large epidemic of leptospirosis was anticipated in September 1990 because flood has resulted the heavy rain for 4 consecutive days from the 8th of September, 1990, in the Yang-pyeung Gun (Country), a farm area of Central Korea. Actually, patients were already appearing sporadically soon after the flood. Soldiers of ROK Army units stationed in this area were under the higher risk since many of them participated in field works (such as tieing rice plant fallen by the flood) as a part of Civil Aid Plan. The objectives of this study were 1) to detect infected ones at early stage 2) to estimate the attack rates of infection and apparent infection through serologic examinations, 3) to estimate pathogenecity and case-fatality rate and 4) to compare the rates of infection by the type of work and the use of protective devices. All of those with febrile episode were interviewed and the leptospiral antibody was examined during the one month period after the field work. Serologic examinations (including the interview) were done twice with 1 week interval (first on 8th to 10th of October, about 4 weeks following the days of field work) for 446 soldiers belong to three companies stationed in the country area. The serologic test (Microscopic agglutination test) were performed with 4 strains. Icterohemorrhagiae lai and Canicola canicola Hond Utrecht IV as standard strains, and 6P-049-1 and YP-35-1 as strains isolated in Korea in 1986, in accordance with WHO guideline. The results are as follows. 1. Among 57 febrile, suspected cases, 37 had serological tests twice and, 20 of them (54.1%) were serologically confirmed to be infected whereas among other 20 subjects who had single serological test, only 2 persons (10.0%) were serologically positive. 2. The dates of onset of fever in confirmed cases were clustered in 10 to 20 days from late September to early October, which coincided well with the duration of exposure (Sep. 13-18). 3. The attack rate of infection and apparent infection were estimated to be 11.2% (95% C. I. ; 8.3-14.1%), 1.8% (95% C. I. ; 0.7-3.1%). Pathogenecity and case-fatality rate were estimated to be 16.0% (95% C. I. ; 6.0-26.0%) and 0%, respectively. 4. The attack rate of infection of persons who worked in rice paddy for 3-6 days, for 1-2 days and participated in other field work were 3.5, 2.7 and 2.1 time high respectively as high as that of persons who did not join in field work (p<0.05). 5. The effectiveness of protective devices shown in this study was rater poor; perhaps the preparation of the protective devices was not sufficient because the mobilization of army is usually a sudden order. For more satisfactory prevention in the future, a complete clothing (including glove and boots) and chemoprophyaxis (with doxycycline) are recommended.
Keywords: Leptospirosis epidemic, Monitoring cases, Attack rate, Risk factor, Prevention


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