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3 "Attack rate"
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An Epidemiologic Study on the Leptospiral Infection in the Period of an Anticipated Epidemic
Bo Youl Choi, Dae Eun Chung, Soo Jin Lee, Hung-Bae Park, Jeoung Bae Park, Kyung Hee Lee, Jeong Soon Kim
Korean J Epidemiol. 1992;14(1):91-101.   Published online June 30, 1992
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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.
Summary
Original Articles
An Epidemiologic Investigation of Shigellosis Outbreak in Gangnung 1998.
Sang Hyuk Jung, Woong Sub Park
Korean J Epidemiol. 2000;22(1):1-10.
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Abstract
An epidemiologic investigation was carried out to identify the distribution and the cause of Shigellosis outbreak, which was occurred in Gangnung city from August to November, 1998. This study carried out from September, 14, to November, 20, 1998. The total number of Shigellosis confirmed patient is 87. We surveyed and obtained the stool sample from all suspected patients and their members of household. The major findings of this study are as follows. 1. The first patient appeared in September 11 and the number of patients increased to September 13, that is peak time, and the patient number tailed down apparently from September, 18, 1998. 2. The incidence rate per 1,000 is largest in Wangsan-Myeon Doma-Ri(32.9), and second largest in Wangsan-Myeon Mokgea-Ri(31.6), The total incidence rate in Gangnung-shi is 0.4(0.4 for man and 0.3 for woman). The age group with the largest incidence rate per 1,000 is 5-14 age group whose incidence rate is 1.4. 3. The secondary generation attack rate in confirmed patient family is 20.6%, and the secondary attack is 7.8%. 4. We considered the meal of school, environmental factor, milk, carrier of Shigellosis as the cause of outbreak, but we were not able to identify the bacteria of shigellosis. But we suspected the meal of school that played important role in outbreak, because outbreak occurred explosively after students ate the meal of school. 5. We considered three hypotheses for the cause of the outbreak. First, a propagation from external regions; Second, an outbreak from contaminated foods; Third, a propagation from carriers in Gangnung. In order to obtain the further information for first and third hypothesis, we should perform PFGE(Pulsed-field gelectrophoresis) with the shigella bacteria of each epidemic region.
Summary
An Epidemiologic Investigation on the Mode of Transmission of the Lethal Salmonellosis Outbreak in Hamyang County.
Jang Rak Kim, Sang Won Lee, Hong Bin Kim, Jin Cha, Kwang Hyun Lee, Kang Woo Bae
Korean J Epidemiol. 1999;21(2):185-194.
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Abstract
An outbreak of Salmonella enteritidis epidemic involving about 200 inpatients of gastroenteritis and 1 death occurred among about 750 participants from Hamyang County who attended 4 wedding lunch parties at one buffet restaurant on April 25, 1999. There were also many patients including 1 death among about 500 participants outside Hamyang County who attended same parties. Person to person interviews made to 155 inpatients revealed that distribution of incubation periods was between 1 to 34 hours with median time, 13-14 hours. A retrospective cohort study was conducted to investigate the mode of transmission. Telephone interviews were made to party participants (except 61 inpatients who already had been interviewed personally) on symptoms and on which they had eaten among 40 served foods including water at the parties and data among 288 persons were available for the analyses. One hundred and ninety one interviewees had more than two symptoms among symptoms of diarrhea(more than 3 times), abdominal pain, and fever, which gave an attack rate of 66.3%(191/288). The relative short incubation period and high attack rate suggested the presence of higher infecting dose in this epidemic. Logistic regression analysis revealed that the probable infective foods were boiled cockle, gamju, boiled midodok, fried rices, eomook, and boiled pig's trotter. Salmonella enteritidis were identified in the specimens of boiled cockle, cooked beef, and uncooked beef. Only boiled cockle was both an epidemiological and microbiological infective food. There might be cross-contaminations between several served foods, which meant presence of many contaminated foods by Salmonella enteritidis with different stage of their multiplications. Efforts to inspect food service areas and educate foodhandlers in good personal hygiene and proper foodhandling practices should be strengthened to reduce the incidences of salmonellosis in Korea.
Summary

Epidemiol Health : Epidemiology and Health