Comparison of Active and Passive Surveillance of Dengue in Machala, Ecuador

Dengue is a major emerging infectious disease, endemic throughout the tropics and subtropics, with approximately 2.5 billion people at risk globally. Active (AS) and passive surveillance (PS), when combined, can improve our understanding of dengue’s complex disease dynamics to guide effective, targeted public health interventions. The objective of this study was to compare findings from the Ministry of Health (MoH) PS to a prospective AS arbovirus research study in Machala, Ecuador from 2014-2015. Dengue cases in the PS system were compared to laboratory confirmed acute dengue illness cases that entered the AS study during the study period. Variables of interest included age, class, and sex. Outbreak detection curves by epidemiologic week, overall cumulative incidence and age-specific incidence proportions were calculated. Descriptive statistics were tabulated for all variables of interest. Chi-square tests were performed to compare demographic characteristics between the AS and PS data sets in 2014 and 2015. 177 and 245 cases were identified from January 1, 2014 to December 31, 2015 by PS and AS, respectively; nine cases appeared in both systems. AS identified a greater number of laboratory-confirmed cases in 2014, accounting for more than 60% of dengue illness cases in the study area. In 2015, the opposite trend was observed with PS identifying 60% of the dengue illness cases in the region. Younger patients were more frequently identified by PS, while older patients were identified more frequently by AS. The cumulative incidence proportion for laboratory confirmed dengue illness reported via PS to the MoH was 4.12 cases per 10,000 Machala residents in 2014, and 2.21 cases per 10,000 Machala residents in 2015. Each surveillance system captured different demographic subgroups within the Machala population, possibly due to differences in healthcare seeking behaviors, access to care, emerging threats of other viruses transmitted by the same mosquito vector and/or differences in clinical presentation due to changes in the predominant dengue serotype in circulation. Integrating AS with pre-existing PS can aid in identifying additional cases in previously under diagnosed subpopulations, improving our understanding of disease dynamics, and facilitating the implementation of public health interventions to reduce the burden of disease.