Larval Indices of Vector Mosquitoes as Predictors of Dengue Epidemics: An Approach to Manage Dengue Outbreaks Based on Entomological Parameters in the Districts of Colombo and Kandy, Sri Lanka

Background. Early detection of dengue epidemics is a vital aspect in control programmes. Predictions based on larval indices of disease vectors are widely used in dengue control, with defined threshold values. However, there is no set threshold in Sri Lanka at the national or regional levels forAedeslarval indices. Therefore, the current study aimed at developing threshold values for vector indices in two dengue high-risk districts in Sri Lanka.Methods. Monthly vector indices (House Index [HI], Container Index [CI], Breteau Index forAedes aegypti[BIagp], andAe. albopictus[BIalb]), of ten selected dengue high-risk Medical Officer of Health (MOH) areas located in Colombo and Kandy districts, were collected from January 2010 to June 2019, along with monthly reported dengue cases. Receiver Operating Characteristic (ROC) curve analysis in SPSS (version 23) was used to assess the discriminative power of the larval indices in identifying dengue epidemics and to develop thresholds for the dengue epidemic management.Results. Only HI and BI(agp)denoted significant associations with dengue epidemics at lag periods of one and two months. Based onAe. aegypti, average threshold values were defined for Colombo as Low Risk (2.4 <= BIagp<3.8), Moderate Risk (3.8 <= BIagp<5), High Risk (BIagp >= 5), along withBIagp 2.9 <= BIagp<4.2(Low Risk),4.2 <= BIagp<5.3(Moderate Risk), andBIagp >= 5.3(High Risk) for Kandy. Further,5.5 <= HI<8.9,8.9 <= HI<11.9, andHI >= 11.9were defined as Low Risk, Moderate Risk, and High Risk average thresholds for HI in Colombo, while6.9 <= HI<9.1(Low Risk),8.9 >= HI<11.8(Moderate Risk), andHI >= 11.8(High Risk) were defined for Kandy.Conclusions. The defined threshold values forAe. aegyptiand HI could be recommended as indicators for early detection of dengue epidemics and to drive vector management activities, with the objective of managing dengue epidemics with optimal usage of financial, technical, and human resources in Sri Lanka.