Short Report: Adult Aedes abundance and risk of dengue transmission

Dengue is transmitted mainly by the adult female Aedes aegypti mosquito. However, little is known about the impact of adult Aedes abundance on the risk of dengue transmission. Here we analysed nationally representative dengue case and vector surveillance data collected from Singapore, to determine the effect of adult Aedes abundance on the risk of dengue transmission. A case was an area with active dengue transmission as indicated by the presence of dengue cluster. A control was an area where no dengue cluster was reported. Using multivariate logistic regression, we analysed 88 cases and 602 controls and estimated the odds of dengue cluster formation at various adult Aedes abundance levels, estimated by the mean number of adult female Aedes per Gravitrap per week and categorised into Low, Moderate, High and Very High abundance level. We found that the risk of dengue cluster formation was positively associated with adult Ae. aegypti abundance. We observed a three to four-fold increase in the odds of dengue clusters forming in areas with High (AOR: 3.40, 95% CI: 2.09, 5.52) and Very High (AOR: 3.99, 95% CI: 2.46, 6.46) adult Aedes aegypti abundance level compared to those with low Ae. aegypti abundance level. Our study strengthens the evidence for the use of adult Aedes indices for dengue risk assessment and early warning for dengue outbreaks. Entomological indicators of adult Ae. aegypti could be used to anticipate and prioritize areas for dengue control. Author summary The House Index and Breteau index are the most widely used indices for vector surveillance. However, the appropriateness of these larval indices has been questioned as they have not been satisfactorily linked to disease transmission. Indices based on actual counts of adult Aedes are likely to be more useful in assessing transmission risk, but the adult Aedes population is rarely sampled as such sampling is perceived as time-consuming and difficult. In this study, which used national data from Singapore, we investigated the effect of adult Aedes abundance on the risk of dengue transmission. We found that areas with high Ae. aegypti abundance had a higher odds of dengue cluster formation. Our study findings suggest that the adult Ae. aegypti abundance can allow early identification of geographical localities at high risk of dengue transmission and thus, a useful indicator to anticipate and prioritize areas for dengue control.

Automated summary

Our study found a positive association between adult Ae. aegypti abundance and the risk of dengue cluster formation, with areas of high and very high adult Aedes abundance levels having significantly higher odds of dengue clusters forming. Adult Aedes indices could be a valuable tool for dengue risk assessment and early warning for outbreaks.