Statistical modeling of the effect of rainfall flushing on dengue transmission in Singapore

Abstract

BackgroundRainfall patterns are one of the main drivers of dengue transmission as mosquitoes require standing water to reproduce. However, excess rainfall can be disruptive to the Aedes reproductive cycle by “flushing out” aquatic stages from breeding sites. We developed models to predict the occurrence of such “flushing” events from rainfall data and to evaluate the effect of flushing on dengue outbreak risk in Singapore between 2000 and 2016.MethodsWe used machine learning and regression models to predict days with “flushing” in the dataset based on entomological and corresponding rainfall observations collected in Singapore. We used a distributed lag nonlinear logistic regression model to estimate the association between the number of flushing events per week and the risk of a dengue outbreak.ResultsDays with flushing were identified through the developed logistic regression model based on entomological data (test set accuracy = 92%). Predictions were based upon the aggregate number of thresholds indicating unusually rainy conditions over multiple weeks. We observed a statistically significant reduction in dengue outbreak risk one to six weeks after flushing events occurred. For weeks with five or more flushing events, compared with weeks with no flushing events, the risk of a dengue outbreak in the subsequent weeks was reduced by 16% to 70%.ConclusionsWe have developed a high accuracy predictive model associating temporal rainfall patterns with flushing conditions. Using predicted flushing events, we have demonstrated a statistically significant reduction in dengue outbreak risk following flushing, with the time lag well aligned with time of mosquito development from larvae and infection transmission. Vector control programs should consider the effects of hydrological conditions in endemic areas on dengue transmission.

The time series seasonal patterns of dengue fever and associated weather variables in Bangkok (2003-2017)

“…Also, stagnant water and poor sanitary and hygiene practices may make suitable breeding sites for the mosquitoes. In contrast, heavy rainfall may wash away breeding sites, interrupt the development of mosquito eggs or larvae [21]. The seasonal pattern indicates that the peak of the dengue-endemic in Bangkok usually occurs in November during the study period, which is generally outside the rainy season.…”

The effects of seasonal climate variability on dengue annual incidence in Hong Kong: A modelling study

“…Rainfall has been generally thought to be a positive predictor of dengue vector abundance as it provides essential mosquito habitats 11,14 . Recent studies, however, have demonstrated that excess rain may also flush away eggs, larvae or pupae of mosquitoes and remove mosquito breeding sites 15,16 , hence negatively effecting dengue incidence. Another study has found that dry seasons followed by a period of excess rainfall can lead to a high risk of dengue outbreaks, indicating that either positive or negative effects can occur, however, with different time lags 17 .…”

Impact of Climate Variability and Abundance of Mosquitoes on Dengue Transmission in Central Vietnam

“…Rainfall provides a water source that serves as a breeding site for female mosquitoes and an environment for immature larva/pupa, resulting in abundant mosquitoes and dengue outbreaks [11,12]. However, a large amount of rain may have a flushing effect, increasing the mortality rate of adult mosquitoes and larvae [13,14]. Temperature plays a major role in the development, survival, and feeding behavior of mosquitoes and encourages viral replication inside the vector [11].…”