Gravitrap Deployment for Adult Aedes aegypti Surveillance and its Impact on Dengue Cases

House Index, Container Index, and Breteau Index are the most commonly used indices for dengue vector surveillance. However, these larval indices are a poor proxy for measuring the adult population-which is responsible for disease transmission. Information on the adult distribution and density are important for assessing transmission risk as well as for developing effective control strategies. This study introduces a new entomological index, Gravitrapaegyptiindex (GAI), which estimates the adult femaleAedes aegyptipopulation in the community and presents its association with dengue cases. Gravitraps were deployed across 34 treatment sites in Singapore from September 2013 to September 2016. The GAI, derived from the Gravitrap surveillance data, was analysed to investigate the spatio-temporal patterns of theAe.aegyptipopulation in Singapore. The index was further categorised into low, moderate, and high-risk groups and its association with dengue cases were examined. A Before-After Control Impact analysis was performed to evaluate the epidemiology impact of Gravitrap system on dengue transmission. TheAe.aegyptipopulation exhibits a seasonal pattern, and spatial heterogeneity inAe.aegyptiabundance was observed among treatment sites. TheAe.aegyptipopulation was also found to be unevenly distributed among floors of an apartment block, with low floors (floors 1-4) having a higher abundance of mosquitoes trapped than mid (floors 5-8) and high (floors >= 9) floors. Areas with high GAI were shown to have higher dengue case count. Gravitrap has also demonstrated to be a good dengue control tool. The contribution of cases by treatment sites to the national numbers was lower after Gravitraps deployment. The GAI, which is of better relevance to dengue transmission risk, could be recommended as an indicator for decision making in vector control efforts, and to monitor the spatio-temporal variability of the adultAedespopulation in the country. In addition, findings from this study indicate that Gravitraps can be used as a dengue control tool to reduce dengue transmission. Author summary In the absence of an effective vaccine: vector surveillance and control remain the key strategy for dengue prevention and control. The collection of the adult femaleAedesmosquito is thus important to understand disease transmission dynamics. Information on its distribution and density are also essential for assessing transmission risk as well as for devising an effective control strategy. Here, we described a new approach to dengue vector surveillance based on adult femaleAedestrapping using Gravitraps. Using the Gravitrap surveillance data, we derived a new entomological index, Gravitrapaegyptiindex (GAI), which estimates the adult femaleAe.aegyptipopulation in the community and presents its association with dengue cases. When analysed, the index can provide useful information on the spatio-temporal distribution of theAe.aegyptipopulation in the country and hence, assist planning of vector control. The GAI, which is of better relevance to dengue transmission risk, could be used as an indicator for decision making in vector control efforts, and to monitor the spatio-temporal variability of the adultAedespopulation. In addition, findings from this study indicate that Gravitraps can be used as a dengue control tool to reduce dengue transmission.