Abstract
BackgroundDespite intensive vector control efforts, dengue epidemics continue to occur throughout Southeast Asia in multi-annual cycles. Weather is considered an important factor in these cycles, but the extent to which the El Niño-Southern Oscillation (ENSO) is a driving force behind dengue epidemics remains unclear.MethodsWe examined the temporal relationship between El Niño and the occurrence of dengue epidemics, and constructed Poisson autoregressive models for incidences of dengue cases. Global ENSO records, dengue surveillance data, and local meteorological data in two geographically diverse regions in Thailand (the tropical southern coastal region and the northern inland mountainous region) were analyzed.ResultsThe strength of El Niño was consistently a predictor for the occurrence of dengue epidemics throughout time lags from 1 to 11 months in the two selected regions of Thailand. Up to 22% (in 8 northern inland mountainous provinces) and 15% (in 5 southern tropical coastal provinces) of the variation in the monthly incidence of dengue cases were attributable to global ENSO cycles. Province-level predictive models were fitted using 1996-2004 data and validated with out-of-fit data from 2005. The multivariate ENSO index was an independent predictor in 10 of the 13 studied provinces.ConclusionEl Niño is one of the important driving forces for dengue epidemics across the geographically diverse regions of Thailand; however, spatial heterogeneity in the effect exists. The effects of El Niño should be taken into account in future epidemic forecasting for public health preparedness.
Highlights
Despite intensive vector control efforts, dengue epidemics continue to occur throughout Southeast Asia in multi-annual cycles
Despite intensive vector control efforts, large periodic dengue epidemics have continued to occur throughout the region in multi-annual cycles [3,4]
Descriptive epidemiology From January 1996 through December 2005, a total of 54,051 and 44,176 dengue cases were reported in the southern coastal and the northern inland regions, respec
Summary
Despite intensive vector control efforts, dengue epidemics continue to occur throughout Southeast Asia in multi-annual cycles. Despite intensive vector control efforts, large periodic dengue epidemics have continued to occur throughout the region in multi-annual cycles [3,4]. Southern Oscillation (ENSO), an ocean-atmosphere phenomenon of the Pacific Ocean with a semi-periodic multiannual cycle [5,6,7], has been hypothesized to be a driving force behind the dengue epidemics in regions at risk through its profound influence on the local climate [8,9]. Studies in the Pacific Islands, French Guiana, and Indonesia showed that El Niño was associated with an increase in annual numbers of reported dengue cases [12,13,14]. From 1995 to 2003, the ENSO cycle was found to predict the subsequent weekly incidence of dengue cases in two municipalities in Mexico with 16-week and 20-week lags, respectively [9]
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