9.3 Entomological Surveillance

Figure 9.9: Spatial Distribution of Breeding Percentage (i.e., BP)

The Aedes house index is not useful when it is lower than 1%. Hence, there is a need for a novel indicator: the novel index.

Figure 9.10: Gravitrap Surveillance in the Public

Figure 9.11: Gravitrap Surveillance Systems Around Singapore

Note that the GAI represents the Gravitrap Aegypti Index: the number of Aegypti cases caught per trap per week.

Figure 9.12: Mean Monthly Number of Sectors with GAI Levels

The above graphic also suggests that there is a 20% increase in GAI sectors in 2020 relative to 2019.

Figure 9.13: Risk Factors of Dengue Vectors

Figure 9.14: Distribution of A. aegypti Vectors per HDB Level

On a national level, A. aegypti and A. albopictus trends are important for public communications and community mobilization to aid in reductions.

On a local level, such distributions of mosquitoes can aid in guiding and prioritizing inspections for source removal and detection.

9.3.1 Effects of gravitrap deployment

Figure 9.15: Reduction in Case Ratios Before and After Gravitrap Sentinel Sites

Figure 9.16: More Information on Gravitrap Sentinel Sites

Based on BACI analysis, there is about a 36% reduction in case burdens.

Figure 9.17: Lull in 2021

The above lull is expected to wane by 2022; a gradual rise in the GAI suggests an increased risk of catching dengue fever. However, the GAI and case counts may not correlate because of other factors.

We predict the lull to be from cross-protection from previous outbreaks.

Figure 9.18: Population-Level Cross-Protection to DENV-3 Waning

The above reduction in DENV-3 is estimated to last about 30 weeks to 80 weeks because of cross protection from DENV-1 and DENV-2 respectively.

However, this protection against DENV-3 from the DENV-1/2/3 outbreak in 2019 to 2020 has likely waned by now!