Dengue in Thailand and Cambodia: An Assessment of the Degree of Underrecognized Disease Burden Based on Reported Cases

Background: Disease incidence data are needed to guide decision-making for public health interventions. Although dengue is a reportable disease in Thailand and Cambodia, the degree that reported incidence underrecognizes true disease burden is unknown. We utilized dengue incidence calculated from laboratory-confirmed outpatient and inpatient cases in prospective cohort studies to estimate the magnitude of dengue underrecognition and to establish more accurate disease burden estimates for these countries. Methods and Findings: Cohort studies were conducted among children aged 95,000 children in Thailand and >58,000 children in Cambodia were estimated to be hospitalized due to dengue. Conclusion: Calculating MFs by comparing prospective cohort study data to locally-reported national surveillance data is one approach to more accurately assess disease burden. These data indicate that although dengue is regularly reported in many countries, national surveillance data significantly underrecognize the true burden of disease. Author Summary: Dengue is a major public health problem especially in tropical and subtropical countries of Asia and Latin-America. An effective dengue vaccine is not yet available, but several vaccine candidates are currently being evaluated in clinical trials. Accurate country-level incidence data are crucial to assess the cost-effectiveness of such vaccines and will assist policy-makers in making vaccine introduction decisions. Existing national surveillance systems are often passive and are designed to monitor trends and to detect disease outbreaks. Our analyses of data from prospectively followed cohorts with laboratory confirmation of dengue cases show that, in Thailand and Cambodia, dengue incidence is underrecognized by more than 8-fold. The magnitude of the outpatient burden caused by dengue is not assessed or reflected by the national surveillance data. We estimate that a median of more than 340,000 symptomatic dengue virus infections occurred annually in children less than 15 years of age in Thailand in Cambodia between 2003 and 2007.