What does dengue disease surveillance contribute to predicting and detecting outbreaks and describing trends?

OBJECTIVE To review the evidence on the application of tools for dengue outbreak prediction/detection and trend monitoring in passive and active disease surveillance systems in order to develop recommendations for endemic countries and identify research needs. METHOD Systematic review of literature in the Cochrane Database of Systematic Reviews, PubMed, EMBASE, Lilacs, WHO library database, manual reference search and grey literature. Two reviewers independently applied pre-defined inclusion and exclusion criteria and assessed the level of evidence. Studies describing the outcome of dengue disease surveillance with respect to trend monitoring and outbreak prediction/detection based on empirical data were included. RESULTS Twenty-four studies (of 1804 references) met the eligibility criteria. Different indicators and their respective threshold values were identified as potential triggers for outbreak alerts through retrospective analysis of data from passive and/or active surveillance systems. Some indicators are potentially useful for predicting imminent outbreaks in the low transmission season and others for detecting outbreaks at an early stage. However, the information collected is mainly retrospective and often site-specific and appropriate levels of sensitivity and specificity of the outbreak indicators/triggers could not be determined. Retrospective and prospective virus surveillance studies were not conclusive regarding the question of whether a newly introduced serotype is an outbreak predictor, but contributed additional indicators for outbreak prediction/detection. Under-reporting was a major concern. Taking cost and feasibility issues into account, it remains an open question whether dengue surveillance should be passive (based on routine reporting) or active (based on more costly sentinel or other active population based surveillance systems). Adding active surveillance elements to a well-functioning passive surveillance system improves sensitivity; adding laboratory elements to the system improves specificity. CONCLUSIONS In view of the lack of evidence about the most feasible and sustainable surveillance system in a country context, countries could use a stepwise approach to locally adapt their passive routine surveillance system into an improved combined active/passive surveillance approach. Prospective studies are needed to better define the most appropriate dengue surveillance system and trigger for dengue emergency response.