Abstract
Dengue is hyper-endemic in Singapore and Malaysia, and daily movement rates between the two countries are consistently high, allowing inference on the role of local transmission and imported dengue cases. This paper describes a custom built sparse space–time autoregressive (SSTAR) model to infer and forecast contemporaneous and future dengue transmission patterns in Singapore and 16 administrative regions within Malaysia, taking into account connectivity and geographical adjacency between regions as well as climatic factors. A modification to forecast impulse responses is developed for the case of the SSTAR and is used to simulate changes in dengue transmission in neighbouring regions following a disturbance. The results indicate that there are long-term responses of the neighbouring regions to shocks in a region. By computation of variable inclusion probabilities, we found that each region’s own past counts were important to describe contemporaneous case counts. In 15 out of 16 regions, other regions case counts were important to describe contemporaneous case counts even after controlling for past local dengue transmissions and exogenous factors. Leave-one-region-out analysis using SSTAR showed that dengue transmission counts could be reconstructed for 13 of 16 regions' counts using external dengue transmissions compared to a climate only approach. Lastly, one to four week ahead forecasts from the SSTAR were more accurate than baseline univariate autoregressions.
Highlights
Malaysia and Singapore are populated by around 38 million people
Granger causality test (GCT) indicated that other regions counts are significantly Granger caused to dengue transmission counts in eight out of 16 regions: Johor, Kedah, Negeri Sembilan, Pahang, Perak, Sarawak, Singapore and Terengganu through the connectivity matrix parameterization
A likelihood ratio test comparing a linear model with only past dengue counts and climatic variables versus the STAR showed that the observed distribution of dengue transmissions to be better explained with the STAR in four out of 16 regions: Johor, Pahang, Selangor and Singapore
Summary
Malaysia and Singapore are populated by around 38 million people. In both countries, dengue is classified as hyper-endemic due to all four dengue serotypes being in active circulation, putting most individuals at risk of dengue infection, and creating considerable health and economic burdens [1,2]. Vector control remains the primary public health intervention, targeting the two dominant dengue mosquito vectors, Aedes aegypti and Ae. albopictus, which are endemic to both countries [5,8]. The timing and scale of these interventions are critical for effective epidemic mitigation and warning systems and require an understanding of the spatial patterns of dengue transmission and the risk of spillover of epidemics from one region to another
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