Dengue epidemiology in selected endemic countries: factors influencing expansion factors as estimates of underreporting

OBJECTIVE: Dengue fever is globally considered underestimated. This study provides expansion factors (EFs) for dengue endemic selected countries and highlights critical issues in the use of EFs. METHODS: We identified dengue epidemiological cohort studies from 2000 to July 2013 through a literature search using PubMed, Web of Science and Lilacs (Latin American and Caribbean Health Sciences Database), pre-defined keywords and inclusion/exclusion criteria, and included Brazil, Colombia, Nicaragua, Peru, Puerto Rico, Venezuela, Bangladesh, Cambodia, India, Indonesia, Philippines, Singapore, Sri Lanka, Thailand and Vietnam. Dengue national and local passive surveillance data were derived from WHO regional websites, PAHO, SEARO and WPRO. EFs were calculated as CI cohort studies/CI passive data for both national and local levels. RESULTS: Cohort studies differed in case definition, laboratory test used and surveillance methods. The information on SEARO, PAHO and WPRO websites differed in terms of dengue epidemiological variables, population denominators and completeness. The highest incidence was reported by PAHO countries followed by WPRO and SEARO countries. EFs may vary for the different variables and denominators used for calculation. EFs were the highest in SEARO countries and lowest in PAHO countries. A trend for lower local EFs was observed. CONCLUSIONS: The use of EFs for quantifying dengue underreporting may be problematic due to lack of uniformity in reporting dengue both active and passive surveillance data. Quality dengue surveillance data are urgently needed for a better estimate of dengue disease burden and to measure the impact of preventive intervention.