Derek A.T. Cummings, University of Pittsburgh Graduate School of Public Health and Johns Hopkins Bloomberg School of Public Health Timothy P. Endy, Walter Reed Army Institute of Research Ananda Nisalak, Armed Forces Research Institute of Medical Sciences Donald Burke, University of Pittsburgh Graduate School of Public Health Spatial coherence and association of temperature, rainfall and the incidence of dengue hemorrhagic fever in Thailand

Research Question How is climate variation associated with the incidence of dengue hemorrhagic fever? Does the dengue season occur at the same time as the rainy season or hot season across Thailand?

Effects of Temperature and Rainfall on Dengue Incidence Temperature Affects -Extrinsic incubation period of virus -Survival rates of mosquito vector -Biting rates of mosquito -Fecundity of mosquito vector Rainfall Affects -Survival rates of mosquito vector -Fecundity of mosquito vector

OOOXX OOOOO OOXXX OOXXX OXXXX DEG C DAYS INCUBATION X = TRANSMISSION, O = NONE Watts et al, 1987

Monthly DHF Incidence Passive Surveillance 72 Provinces Gathered by Thai Ministry of Public Health, serologically confirmed to the extent logistically possible. (~20%) Roughly 850,000 cases Source of Incidence Data

NSNS Log(Incidence/1000) Rank of Province Year Normalized Log of Raw Incidence of DHF in Thailand

Monthly Mean Temperatures and Monthly Rainfall for 52 weather stations in 41 provinces NOAA Climate Anomaly Monitoring System Source of Weather Data

The timing of the DHF season is associated with the timing of the rainy or warm seasons First Hypothesis

DHF Incidence Temperature Rainfall Spatial Synchrony of DHF, Temperature and Rainfall

NSNS Log(Incidence/1000) Rank of Province Year Normalized Log of Raw Incidence of DHF in Thailand

Decomposition of Time Series Using the Empiric Mode Decomposition

Seasonal Mode of DHF Incidence

Phase Differences

p<0.003 R 2 =0.2 Mean Phase Difference of Seasonal Mode of DHF Incidence vs. Mean Phase Differences of Rainfall

Temperature The timing of changes in ambient temperature are not associated with the timing of the dengue season in the same analysis

Annual DHF incidence is related to annual means of temperature or annual totals of rainfall Used a two-stage hierarchical model to generate pooled estimates of the association between Annual mean temperature, annual total rainfall and total annual DHF incidence across the entire country Second Hypothesis

Used a two-stage hierarchical model to generate pooled estimates of the association between annual mean temperature, annual total rainfall and total annual DHF incidence across the entire country Higher Mean Annual Temperatures are statistically significantly associated with higher Annual DHF Incidences (p<10-4) Modified by Mean Temperatures (p<0.04) and Distance from Bangkok (p<10-5)

Beta’s from Generalized Linear Model of Annual Incidence on Temperature vs. Distance from Bangkok Beta Coefficients from Linear Regression of Annual DHF Inc on Temp. Annual Mean Temperatures

Only monthly data is available. May not be able to detect association between small changes in the timing of seasons Association may be non-linear, with thresholds above or below which, variation is less important Seasonal process may not be separable from underlying intrinsic dynamics Difficulties with this Analysis

Higher mean annual temperatures are associated with higher incidences of DHF across Thailand and are modified by mean temperature and distance from Bangkok The phase of the dengue seasonal variance in DHF incidence is associated with the phase of rainfall across Thailand Conclusions

Average proportion of countrywide DHF cases per month

Relative timing of rainy season and the dengue season regional

Examine weekly data available from later years Examine correlation structure of each of these variables Next Steps

Thank you