Validation of the Early Warning and Response System (EWARS) for dengue outbreaks: Evidence from the national vector control program in Mexico

BackgroundDuring 2017, twenty health districts (locations) in Mexico implemented a dengue outbreak early warning and response system (EWARS) that uses epidemiological, meteorological and entomological variables (alarm indicators) to predict dengue outbreaks and triggers early response activities. Eleven of these districts were analyzed as they presented reliable information. Nine districts presented outbreak alarms but without subsequent outbreaks ("non-outbreak districts") and two presented after the alarms dengue outbreaks ("outbreak districts"). This study is concerned with i) if the alarms without outbreaks were false alarms or if the control services had established effective response activities averting an outbreak and ii) if vector control activities can mitigate or even avert dengue outbreaks. MethodsFive components of dengue outbreak response (larval control, entomological studies with water container interventions, focal spraying, indoor residual spraying, space spraying) were quantitatively analyzed across two groups ("outbreak districts" and "non-outbreak districts"). ResultsThe average coverage of vector control and responses were higher in non-outbreak districts and across all five components. In the "outbreak districts" the response activities started late and were of much lower intensity compared to "non-outbreak districts". District vector control teams demonstrated diverse compliance with local guidlines for initial, early and late responses to outbreak alarms which could explain the different outcomes observed following the outbreak alarms. Conclusionfindings from this study plausibly demonstrates important operational scenarios when succeeding or failing alarms signals generated by EWARS at national level. This study presents evidence warranting for further investigation into the effectiveness and cost-effectiveness of EWARS using gold-standard designs.