The climatic factors influencing DHF occurrence in Thailand

Suwich Thammapalo, The Vector Borne Disease Control Office Region 4, Songkhla
Virasakdi Chongsuvivatwong, Assoc. Prof., Epidemiology Unit, F. of Medicine, PSU.
Don McNeil, Prof., Macquarie U., Sydney, Australia
Alan Geater, Epidemiology Unit, F. of Medicine, PSU.
Corresponding e-mail : cvirasak@ratree.psu.ac.th

Grant : TRF
Published : Research Report
Key words : climatic factors, rainfall, temperature, relative humidity, DHF occurrence

To determine effects of climatic factors : rainfall, temperature and relative humidity, on DHF occurrence in Thailand by time-series analysis modeling. Time-series analysis can demonstrate trends, cyclic pattern and the independent effect of putative factors and can examine autocorrelation within the same province that is more advanced than former statistical methods. Monthly DHF reported cases by province and monthly data on rainfall, rain-days, average maximum temperature, average minimum temperature, average relative humidity and number of mid-year population by province during 1978-1997 (240 months) in 73 provinces were collected. The appropriate equation, Incidence of DHF = constant+trends+cyclic effects+climatic factors+noise of each province, was developed by time-series analysis model. The regression analysis of those models showed only rainfall and maximum temperature to be significantly associated with DHF incidence in 9 and 15 pro-vince, respectively, out of 73 provinces. DHF incidence had a negative association with rainfall in the southern region but a positive association with maximum temperature in the central and northern regions. We conclude that climatic factors do not have consistent effects on the occurrence of DHF. Cyclic effects and trends explain most of the variation.

Further analysis will explore month effect and intra-province correlation and compare climatic association with DHF on east coast and west coast of southern of Thailand.

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