The Relationship between Rainfall and the Incidence of Melioidosis in Thailand’s Health Region 9, Thailand

Abstract

Melioidosis is a significant public health problem, particularly in northeastern Thailand, and is often associated with environmental factors such as rainfall. This study aimed to analyze the quantitative relationship between rainfall and the monthly incidence of melioidosis in four provinces within Thailand’s Health Region 9: Buriram, Chaiyaphum, Nakhon Ratchasima, and Surin. This study employed a correlational design using ecological time-series analysis on secondary monthly data from January 2018 to December 2024 (84 months). Patient data were sourced from the Division of Epidemiology, and rainfall data from the Hydro-informatics Institute (Public Organization). A generalized linear model (GLM) was used for analysis. The Quasi-Poisson model was selected due to severe overdispersion (Chi-squared/DF>3.5) observed in the data from all provinces. The results revealed that maximum rainfall had a positive and significantly correlated with the incidence of melioidosis in Nakhon Ratchasima (p=0.002) and Surin (p=0.001). For every 1 mm. increase in maximum rainfall, the expected incidence rate increased by 0.083% in Nakhon Ratchasima and 0.178% in Surin. However, no significant relationship was found in Buriram (p=0.516) or Chaiyaphum (p=0.794).

The analysis indicated that rainfall impacts melioidosis incidence differently across provinces. It was recommended that maximum rainfall data be used to support early warning systems in Nakhon Ratchasima and Surin. For Buriram and Chaiyaphum, further research on other environmental factors, such as relative humidity or soil characteristics, was suggested.