The Impacts of of Climate Variability on Seasonality, Spatial Variability and Extremes of Dengue Transmission in Sri Lanka : Relationships of El Niño, Indian Ocean Dipole and Warming and Epidemic incidence

Abstract:

Dengue has been endemic in Sri Lanka since 1970’s with perennial occurrence and seasonal peaks. Dengue which was limited to Colombo until around 2000 started to spread to other urban centers and then to peri-urban locales with an epic epidemic in 2017. Here, we examine the regional and seasonal variation of dengue incidence and analyse the influence of temperature and rainfall.

Sri Lanka has an area of 65,000 square kilometers and hosts 21 million. The rainfall climate is bimodal modulated by the passage of the Inter-Tropical Convergence Zone. The regional character is due to the influence of the storm tracks from the Bay of Bengal and that of a mountain massif that rises anchor like to 2532 m.

Data: Epidemiological Data were obtained from the Ministry of Health, meteorological data from the Department of Meteorology and other agencies and Demographic Data were obtained from the Department of Census and Statistics.

Methods: Island level incidence data were aggregated by 9 Provinces, 25 Districts and detailed at Health Sub-Districts and in some areas by villages. Monthly average dengue incidence and rainfall and temperature climate were plotted to build probabilistic multi-variate relationship. Correlation analysis and composite analysis were undertaken between case data and rainfall and temperature with lags and with robust methods.

Seasonality: The monthly average incidence was largely bimodal with a mid-year peak in June-July and an end of the year peak in December-January. While most of the provinces displayed a high June-July peak, the Eastern provinces have a lower mid-year peak.

Epidemics: There is high sensitivity of epidemics to temperature specifically. Epidemics occurs when the minimum and maximum temperatures is between 25-26 °C and 30-31 °C. The recent epic epidemic in 2017 was preceded by a dry season and anomalously dry and anomalously warm temperature due to the Indian Oceanic warming and the Indian Ocean Dipole

This work has characterized the climate drivers of dengue seasonality and epidemics. The seasonality and regional variation of dengue and rainfall is correlated with a lag of 1-2 months with peaks in dengue. The incidence of epidemics occur in a narrow range of temperatures. These findings shall contribute to a climate based early warning risk prediction system.