Combined effects of hydrometeorological hazards and urbanisation on dengue risk in Brazil: a spatiotemporal modelling study

Abstract

Background Temperature and rainfall patterns are known to influence seasonal patterns of dengue transmission. However, the effect of severe drought and extremely wet conditions on the timing and intensity of dengue epidemics is poorly understood. In this study, we aimed to quantify the non-linear and delayed effects of extreme hydrometeorological hazards on dengue risk by level of urbanisation in Brazil using a spatiotemporal model. MethodsWe combined distributed lag non-linear models with a spatiotemporal Bayesian hierarchical model framework to determine the exposure-lag-response association between the relative risk (RR) of dengue and a drought severity index. We fit the model to monthly dengue case data for the 558 microregions of Brazil between January, 2001, and January, 2019, accounting for unobserved confounding factors, spatial autocorrelation, seasonality, and interannual variability. We assessed the variation in RR by level of urbanisation through an interaction between the drought severity index and urbanisation. We also assessed the effect of hydrometeorological hazards on dengue risk in areas with a high frequency of water supply shortages. Findings The dataset included 12 895 293 dengue cases reported between 2001 and 2019 in Brazil. Overall, the risk of dengue increased between 0-3 months after extremely wet conditions (maximum RR at 1 month lag 1•56 [95% CI 1•41-1•73]) and 3-5 months after drought conditions (maximum RR at 4 months lag 1•43 [1•22-1•67]). Including a linear interaction between the drought severity index and level of urbanisation improved the model fit and showed the risk of dengue was higher in more rural areas than highly urbanised areas during extremely wet conditions (maximum RR 1•77 [1•32-2•37] at 0 months lag vs maximum RR 1•58 [1•39-1•81] at 2 months lag), but higher in highly urbanised areas than rural areas after extreme drought (maximum RR 1•60 [1•33-1•92] vs 1•15 [1•08-1•22], both at 4 months lag). We also found the dengue risk following extreme drought was higher in areas that had a higher frequency of water supply shortages.Interpretation Wet conditions and extreme drought can increase the risk of dengue with different delays. The risk associated with extremely wet conditions was higher in more rural areas and the risk associated with extreme drought was exacerbated in highly urbanised areas, which have water shortages and intermittent water supply during droughts. These findings have implications for targeting mosquito control activities in poorly serviced urban areas, not only during the wet and warm season, but also during drought periods.

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“…We included a distributed lag non-linear model formulation using natural cubic spline (NS) in R packages dlnm and splines to quantify the non-linear relationship between each climate factor (var df) with changing dengue risk over different lag periods 0-3 months (lag df; appendix pp 4-7). 20,21 The difference between cases reported in the previous year and mean long-term annual average (over years 2014-19) (annual anomaly [c,a(t) -1] ) was introduced to account for inter-annual immunity changes, where a(t) = 2014,…,2019. We included structured random effects to account for spatial, seasonal, and extra-seasonal variations in unknown and unmeasurable factors (such as differences in health care, vector control, and human mobility).…”

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“…Furthermore, the effects of meteorological conditions are often non-linear 28,29 . In general, biological processes have an optimal range rather than a linear relationship with temperature 30 .…”

The impact of climate suitability, urbanisation, and connectivity on the expansion of dengue in 21st century Brazil

“…These conditions arise when rapid urbanisation occurs without adequate improvements to infrastructure, such as access to piped water and refuse collection [ 16 , 17 ]. There is evidence that areas lacking reliable access to piped water are more susceptible to dengue outbreaks, particularly in highly urbanised areas following drought [ 18 ]. Prior studies have found that extremely wet conditions also increased the risk of dengue outbreaks, thought to be linked to the creation of larval habitat in the short term [ 18 , 19 ].…”

“…There is evidence that areas lacking reliable access to piped water are more susceptible to dengue outbreaks, particularly in highly urbanised areas following drought [ 18 ]. Prior studies have found that extremely wet conditions also increased the risk of dengue outbreaks, thought to be linked to the creation of larval habitat in the short term [ 18 , 19 ]. Suitable temperature conditions are required for the mosquitoes to breed and transmit the virus.…”