Abstract
In recent years, dengue has been rapidly spreading and growing in the tropics and subtropics. Located in southern China, Hong Kong’s subtropical monsoon climate may favour dengue vector populations and increase the chance of disease transmissions during the rainy summer season. An increase in local dengue incidence has been observed in Hong Kong ever since the first case in 2002, with an outbreak reaching historically high case numbers in 2018. However, the effects of seasonal climate variability on recent outbreaks are unknown. As the local cases were found to be spatially clustered, we developed a Poisson generalized linear mixed model using pre-summer monthly total rainfall and mean temperature to predict annual dengue incidence (the majority of local cases occur during or after the summer months), over the period 2002-2018 in three pre-defined areas of Hong Kong. Using leave-one-out cross-validation, 5 out of 6 observations of area-specific outbreaks during the major outbreak years 2002 and 2018 were able to be predicted. 42 out of a total of 51 observations (82.4%) were within the 95% confidence interval of the annual incidence predicted by our model. Our study found that the rainfall before and during the East Asian monsoon (pre-summer) rainy season is negatively correlated with the annual incidence in Hong Kong while the temperature is positively correlated. Hence, as mosquito control measures in Hong Kong are intensified mainly when heavy rainfalls occur during or close to summer, our study suggests that a lower-than-average intensity of pre-summer rainfall should also be taken into account as an indicator of increased dengue risk.
Highlights
IntroductionDengue has been rapidly spreading and growing in the tropics and subtropics
In recent years, dengue has been rapidly spreading and growing in the tropics and subtropics
Despite the successful dengue control measures introduced after the first local case was identified in Hong Kong in 200221, there has been a gradual increase in dengue incidence after 2014 with the highest number of dengue so far recorded in 2018
Summary
Dengue has been rapidly spreading and growing in the tropics and subtropics. The number of cases is still increasing as the disease spreads to new areas and explosive outbreaks occur This global expansion of dengue virus (DENV) can be due to several causes, including environmental and climate factors. This study aims to enable prediction the annual number of dengue cases using seasonal monthly temperature and rainfall data before summer and assessing the effects of climate variability on the recent increase of dengue incidence in Hong Kong. Given that all dengue outbreaks/infections in Hong Kong occurred as either local clusters or sporadic cases in certain areas instead of large regional scale epidemics, the study utilised a generalized linear mixed model that contains area-specific random effects to account for environmental factors which are difficult to measure and fixed effects to account for climate effects on dengue transmission. Understanding how the climate may affect annual dengue incidence is important in order to forecast future possible dengue outbreaks, thereby allowing for more effective mosquito control measures in each region, leading to early preparedness and prevention of dengue
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