A case-crossover study design is a method to assess the effect of transient exposures on the risk of onset of acute events. Which was introduced by Maclure in 1991 for Myocardial Infarction Onset Study. The design has been used to diverse fields of epidemiology such as injury, drug adverse events, air pollution and so on. The most valuable advantage of this design is unnecessary of control selection. To estimate relative risk, the exposure frequency during a window just before outcome onset is compared with exposure frequencies during control times rather than in control persons. One or more control times are supplied by each of the cases themselves. Self-matching of cases eliminates the threat of control-selection bias and increases efficiency. To application of the case-crossover design, we need to make sure several criteria and the possibility of specific bias. This review is designed to help the reader apply a case-crossover study design to their research fields by understanding general ideas, prior conditions and limitations of the design.
Air Pollution ; Bias (Epidemiology) ; Case-Control Studies ; Cross-Over Studies ; Epidemiologic Methods ; Humans ; Imidazoles ; Myocardial Infarction ; Nitro Compounds

PURPOSE: The aim of this study is to investigate the colonization rate of Methicillin-resistant Staphylococcus aureus (MRSA) in neonates by different clinical characteristics, to presume the origin of MRSA acquisition, and to identify the risk factors associated with MRSA colonization. METHODS: We retrospectively reviewed the medical records of 1,733 neonates admitted to Seoul Eulji hospital Neonatal Intensive Care Unit between January 2008 and December 2011. Nasal, inguinal and rectal swab specimens were obtained upon admission and each week until discharge. We classified the route of MRSA acquisition as; hospital associated (HA-MRSA) and community associated (CA-MRSA) according to the case definition. RESULTS: Among 1,733 neonates, 415 (23.9%) were colonized with MRSA. Gestational age, birth weight, delivery type, maternal antibiotics usage before delivery, birth place and care place before admission were influencing factors in colonization of MRSA. The colonization rate was significantly high in neonates without maternal prophylactic antibiotics use before delivery than in the other group (relative risk 2.77, 95% CI 1.88-4.07; P<0.01), and outborns showed higher MRSA colonization rate compared to inborns (relative risk 2.28, 95% CI 1.17-4.42; P=0.015). CONCLUSION: We identified the neonatal MRSA colonization rate to be 23.9%. We estimated HA-MRSA colonization rate to be 10% (51/511) and CA-MRSA colonization rate to be 36% (309/858). We ascertained that risk factors in MRSA colonization in neonates were prophylactic use of antibiotics in mothers and the birth place.
Anti-Bacterial Agents ; Birth Weight ; Colon ; Gestational Age ; Humans ; Hypogonadism ; Infant, Newborn ; Intensive Care, Neonatal ; Medical Records ; Methicillin Resistance ; Methicillin-Resistant Staphylococcus aureus ; Mitochondrial Diseases ; Mothers ; Ophthalmoplegia ; Residence Characteristics ; Retrospective Studies ; Risk Factors ; Staphylococcus aureus

PURPOSE: Since 1997, private postnatal care facilities (San-hu-jo-ri-won in Korean) have emerged to take the role of the family. As a result, neonates are now exposed to many people and are very vulnerable to infection. However, there has been no study on the influence of postnatal care facilities on neonatal infection. The aim of this study was to determine the risk factors of neonatal infection in full-term babies in Korea. MATERIALS and METHODS: We followed up 556 pregnant women and their babies for 4 weeks after their births at 2 hospitals in Seoul and Daejeon from October 2004 to September 2005. Among 512 full-term babies, 58 had infectious diseases. To determine the risk factors for infection, 53 infected neonates at 4-28 days of life and 413 healthy neonates were compared. RESULTS: The incidence of neonatal infection at 4 to 28 days after birth was 10.5%. After adjusting the related factors, the number of siblings (OR = 2.05, 95% CI = 1.13-3.71 for 1 or more) and postnatal care facilities or home aides (OR = 1.91, 95% CI = 1.07-3.45) were significant risk factors. Formula or mixed feeding (OR = 1.66, 95% CI = 0.91-3.04) increased the risk of neonatal infection but it was not statistically significant. CONCLUSION: When the newborns had siblings, stayed at postnatal care facilities, or were cared for by home aides, the risk of neonatal infections significantly increased. Further research on the feeding effect on neonatal infection and evaluation of prevention efforts are needed.
Communicable Diseases/*epidemiology ; Female ; Humans ; Infant, Newborn ; Korea/epidemiology ; Mothers ; Risk Factors ; *Term Birth

The recent outbreak of Middle East respiratory syndrome (MERS) coronavirus infection in Korea resulted in large socioeconomic losses. This provoked the Korean government and the general public to recognize the importance of having a well-established system against infectious diseases. Although epidemiologic investigation is one of the most important aspects of prevention, it has been pointed out that much needs to be improved in Korea. We review here the current status of the Korean epidemiologic service and suggest possible supplementation measures. We examine the current national preventive infrastructure, including human resources such as Epidemic Intelligence Service officers, its governmental management, and related policies. In addition, we describe the practical application of these resources to the recent MERS outbreak and the progress in preventive measures. The spread of MERS demonstrated that the general readiness for emerging infectious diseases in Korea is considerably low. We believe that it is essential to increase society's investment in disease prevention. Fostering public health personnel, legislating management policies, and establishing research centers for emerging infectious diseases are potential solutions. Evaluating international preventive systems, developing cooperative measures, and initiating improvements are necessary. We evaluated the Korean epidemiologic investigation system and the public preventive measures against infectious diseases in light of the recent MERS outbreak. We suggest that governmental authorities in Korea enforce preventive policies, foster the development of highly qualified personnel, and increase investment in the public health domain of infectious disease prevention.
Communicable Diseases* ; Communicable Diseases, Emerging ; Coronavirus Infections ; Foster Home Care ; Humans ; Intelligence ; Investments ; Korea* ; Middle East* ; Public Health

No abstract available.

The recent outbreak of Middle East Respiratory Syndrome (MERS) coronavirus infection in Korea resulted in large socioeconomic losses. This provoked the Korean government and the general public to recognize the importance of having a well-established system against infectious diseases. Although epidemiologic investigation is one of the most important aspects of prevention, it has been pointed out that much needs to be improved in Korea. We review here the current status of the Korean epidemiologic service and suggest possible supplementation measures. We examine the current national preventive infrastructure, including human resources such as Epidemic Intelligence Service officers, its governmental management, and related policies. In addition, we describe the practical application of these resources to the recent MERS outbreak and the progress in preventive measures. The spread of MERS demonstrated that the general readiness for emerging infectious diseases in Korea is considerably low. We believe that it is essential to increase society's investment in disease prevention. Fostering public health personnel, legislating management policies, and establishing research centers for emerging infectious diseases are potential solutions. Evaluating international preventive systems, developing cooperative measures, and initiating improvements are necessary. We evaluated the Korean epidemiologic investigation system and the public preventive measures against infectious diseases in light of the recent MERS outbreak. We suggest that governmental authorities in Korea enforce preventive policies, foster the development of highly qualified personnel, and increase investment in the public health domain of infectious disease prevention.
Communicable Diseases* ; Communicable Diseases, Emerging ; Coronavirus Infections ; Foster Home Care ; Humans ; Intelligence ; Investments ; Korea* ; Middle East* ; Public Health

An economic evaluation of Haemophilus influenzae type b (Hib) immunization was conducted to examine whether Hib immunization should be included in the Korea's national immunization program. The costs and benefits included direct and indirect values and an estimation of the economic efficiency. We determined that a universal Hib immunization program in Korea would prevent 17 deaths and 280 invasive Hib cases. When we assumed the one Hib immunization cost as 26,000 won, the national Hib immunization would cost 34.6 billion won. Costs for various Hib diseases were estimated at 26.8 billion won (11.8 billion won from direct costs and 14.9 billion won from indirect costs). A benefit-cost ratio of 0.77 showed that the economic efficiency of the integration of Hib immunization in Korea is low because of the low incidence rate of Hib disease and high price of vaccine. However, if the Hib immunization cost decrease to less than 20,000 won, a benefit-cost ratio increase to 1.0 and above, integrating Hib immunization into the national immunization program with economic efficiency can be considered.
Child ; Child, Preschool ; Cost of Illness ; Cost-Benefit Analysis ; Decision Support Techniques ; Haemophilus Infections/*economics/*prevention & control ; Haemophilus Vaccines/*economics/*therapeutic use ; Haemophilus influenzae type b/*metabolism ; Humans ; Immunization/*economics ; Immunization Schedule ; Infant ; Korea ; Models, Economic ; State Medicine

PURPOSE: This study was carried out to obtain the immunization rate of MMR, and to know the related factors. METHODS: Subjects of the study were 3,364 students of 8 elementary schools of Kyonggi province. Surveys accompanied with questionnaires were conducted in 1996 and 1999, respectively. RESULTS: The salient features of the findings were as follows : The immunization rate for MMR turned out to increase as the age of students becomes younger and the 2nd MMR coverage rate in the 1999 survey was 30%. The MMR immunization rate had a strong positive correlation with parental education and income levels. The 2nd MMR immunization rate also had a strong positive correlation with the level of parental education. The vaccination record-keeping rate increased from 30% in 1996 to 41% in 1999. Especially, 52% of freshmen had a record in 1999. The record keeping rate had a strong positive correlation with parental education and income levels. Vaccination places for MMR were hospital or clinics in 60% and public health centers in 39%. CONCLUSION: The vaccination coverage rate for MMR was 85.5% in 1996 and 83.0% in 1999, respectively. The immunization rate however was not high enough to be able to protect against the MMR epidemy. In particular, we should pay more attention to vaccinating the children whose parents' education or income level is low. And we need to have a program that will enhance coverage for the 1st and the 2nd MMR among school children.
Child ; Education ; Gyeonggi-do* ; Humans ; Immunization* ; Korea* ; Measles ; Mumps ; Parents ; Public Health ; Surveys and Questionnaires ; Vaccination

Public health emergencies caused by infectious diseases are the greatest threat to mankind in the 21st century, and pose an even more significant threat than nuclear weapons. The first step in preparing for and responding to such public health emergencies is to conduct thorough surveillance and rapid epidemiological investigations. Especially in the case of public health emergencies, most information is not smoothly transmitted. Therefore, it is necessary to evaluate the emergency and to collect data quickly and efficiently by defining the minimum necessary data and information. In addition, these data should be analyzed and interpreted promptly, and countermeasures and strategies should be developed and utilized in preparedness and response activities. Epidemiological investigations should also be carried out promptly in accordance with the emergency situation, and in particular, if the infection source is not known, maximal measures should be taken to prevent epidemiologists from becoming infected. In order to carry out surveillance and epidemiological investigations effectively in the future in the event of a public health emergency, continuous efforts should be made to nurture professional manpower, international cooperation, and use of the latest information technology.
Communicable Diseases* ; Disease Outbreaks ; Emergencies* ; Epidemiology ; International Cooperation ; Nuclear Weapons ; Public Health*

OBJECTIVES: To describe the characteristics of a mumps epidemic in Cheju-do, 1998 and to identify the risk factors associated with mumps infection. METHODS: To estimate attack rate, previously collected data from the Nationally Notifiable Communicable Disease Reporting System and School Health Reporting System, temporarily administered by Division of Education, as well as additional surveillance data were used. In order to identify the clinical characteristics and risk factors associated with mumps, we conducted a questionnaire survey in 17 schools (9 elementary, 4 middle, and 4 high schools) among a population that included healthy students. RESULTS: From March 3 to August 31, 2,195 cases of mumps were identified, and patients under 20 years of age accounted for 2,162 cases (attack rate 13.2, 95% CI 12.6-13.7/1,000). The attack rate for the population under 20 years of age was the highest in Nam county (44.7/1,000), and in the 7-12 years old sub-group(>20.0/1,000). There was no sexual difference. 80.9% and 59.7% of patients presented periauricular and submandibular swelling respectively. Aseptic meningitis was a complication in 2.9% of cases, orchitis in 1.3%, epididymitis in 0.9% and oophoritis in 0.6% respectively. The overall MMR vaccination rate was 59.1% and it decreased in accordance with increasing age. In students aged 10 years old or below, household contact and MMR vaccination status was significantly associated with infection, and only among students with household contact, the risk of one dose MMR(OR=10.22, 95% CI 2.92-35.78) and non-vaccination (OR=11.62, 95% CI 1.96-68.96) was significantly greater when compared with that of two dose vaccination. Among students aged 11 years old or above, household contact history was significantly associated and MMR vaccination status was not associated. CONCLUSIONS: Low vaccination rate and vaccine failure were thought to predispose the population for this large outbreak. To prevent sustained mumps outbreaks, a second MMR vaccination should be encouraged and catch up vaccinations should be given to elderly children who remain susceptible.
Aged ; Child ; Communicable Diseases ; Disease Outbreaks ; Education ; Epididymitis ; Family Characteristics ; Female ; Humans ; Jeju-do* ; Male ; Meningitis, Aseptic ; Mumps* ; Oophoritis ; Orchitis ; Questionnaires ; Risk Factors ; School Health Services ; Vaccination