Methods
Ethics statement
The study protocol was approved by the Ethical Review Committee for Research in Human Subjects, Ministry of Public Health, Thailand, and the Institutional Review Board, International Vaccine Institute, Seoul Korea.
Study site
The study was carried out in the sub-district Namuang (downtown) of Muang district of Ratchaburi province, which is located approximately 100 km west of Bangkok, and lies between the Maeklong River on the east and the Thai-Myanmar border on the west. The sub-district has a population of 38,835 (census 2006) and a total area of 8.7 km2. The principal medical care facility for the province is Ratchaburi Provincial Hospital (RH), a 855-bed tertiary care facility with 90 pediatric beds and 12 pediatricians on staff. In 2005 the hospital served approximately 1,520 outpatients per day. There were 207, 197 and 214 clinically diagnosed dengue patients, admitted to the pediatric dengue ward in 2003, 2004, and 2005, respectively.
Study design
This was a prospective cohort study of children attending 7 primary schools. Schools were selected based on their desire to participate in the study, and location within 6 km from RH and the Provincial Health Office (figure 1). Following school-based informational meetings with parents, informed parental consent and signed assent for children >7 years of age were obtained from potential participants. Enrollment criteria were healthy children, no history of chronic illness, ages 3–11 years (grades 1–5) at the time of enrollment, attendance at one of the study schools, and living in a village of Muang district. Exclusion criteria included intent to move outside of the study area within the study period. Children were eligible to remain in the study until graduation from sixth grade. During each January of the study, new children aged 4–5 years were offered the opportunity to enroll to replace children who graduated from the sixth grade.
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