Features of the urban environment associated with Aedes aegypti abundance in high-rise public apartments in Singapore: An environmental case-control study

Abstract

Aedes aegypti abundance in residential estates is hypothesized to contribute to localised outbreaks of dengue in Singapore. Knowing the factors in the urban environment underlying high Ae. aegypti abundance could guide intervention efforts to reduce Ae. aegypti breeding and the incidence of dengue. In this study, objective data on Ae. aegypti abundance in public apartment blocks estimated by Singapore’s nationally representative Gravitrap surveillance system was obtained from the National Environmental Agency. Low and high abundance status public apartment blocks were classified based on the Gravitrap Aegypti Index, corresponding to the lowest and highest quartiles respectively. An environmental case-control study was conducted, wherein a blinded assessment of urban features hypothesised to form breeding habitats was conducted in 50 randomly sampled public apartment blocks with low and high abundance statuses each. Logistic regression was performed to identify features that correlated with abundance status. A multivariable logistic model was created to determine key urban features found in corridors and void decks which were predictive of the Ae. aegypti abundance status of the public apartment block. At a statistical level of significance of 0.20, the presence of gully traps [Odds Ratio (OR): 1.34, 95% Confidence Interval (CI): 1.10, 1.66], age of the public apartment block [OR: 2.23, 95% CI: 1.48, 3.60], housing price [OR: 0.33, 95% CI: 0.16, 0.61] and corridor cleanliness [OR: 0.67, 95% CI: 0.40, 1.07] were identified as important predictors of abundance status. To reduce Ae. aegypti abundance around public apartment blocks and potential onward dengue transmission, gully traps could be remodelled or replaced by other drainage types. Routine inspections of Ae. aegypti breeding should be targeted at older and low-income neighbourhoods. Campaigns for cleaner corridors should be promoted.

Associations between Dengue Incidence, Ecological Factors, and Anthropogenic Factors in Singapore

“…In particular, urban drainage structures, such as storm drains and gully traps, which retain rainwater and runoff, offer a conducive breeding ground for immature Aedes spp. [ 35 , 36 , 37 ], potentially driving up vector populations, and consequentially, dengue incidence rates. Another viable explanation is that the dispersal of mosquito species such as Aedes that feed on mammals tends to be low [ 38 ].…”

Efficacy ofWolbachia-mediated sterility to suppress adultAedes aegyptipopulations

“…(7) The major open drainage network for Singapore was obtained from the Public Utilities Board and has been previously shown as a key breeding site for mosquitoes around HDBs 26 . The average distance of each HDB block within a sector to a drain was measured as well as the length of the network within the sector.…”

Efficacy ofWolbachia-mediated sterility for control of dengue: emulation of a cluster randomized target trial

“…The percentage cover of built area was calculated as a sum of all residential, commercial and industrial buildings, representing the level of urbanicity, which has been associated with Aedes aegypti presence 14 . (7) The major open drainage network for Singapore was obtained from the Public Utilities Board and has been previously shown as a key breeding site for mosquitoes around public housing apartments 15 . The average distance of each block within a sector to a drain was measured as well as the length of the network within the sector.…”