Spatial diffusion of diarrhea outbreak in Chiang Mai, Thailand

  • Chaikaew N.


The objective of this study was to utilize the space-time permutation scan statistic and GIS for investigating and visualizing the spatial diffusion of diarrhea outbreaks in Chiang Mai province, Thailand. A space-time retrospective analysis was conducted to detect the outbreak signals of diarrhea from 1 November 2003 to 31 October 2006, in order to include all confirmed diarrhea cases of patient less than five years of age. A total of 37,536 diarrhea cases were reported in Chiang Mai from November 1, 2003 to October 30, 2006. In the study period had more village outbreaks and the diarrhea incidence was so high. The strongest signals of outbreak (13 villages) was on 17 January 2006 (cool season) and occurred to the conurbations of Mae Chaem district (Chang Khoeng and Tha Pha sub-districts), which is located about 100 km to the south-west of Chiang Mai City. This signal had 44 cases observed over 8 days when 2.98 were expected (relative risk= 14.79). The weaker signal was on 29 June 2005 (begin of rainy season) that were located in southern Chiang Mai (Chom Thong district), there had 16 cases observed over 11 days when 1.21 were expected theoretically (relative risk= 13.24). The daily spatial spread or diffusion of diarrhea outbreak from the first day to the end day of incidence (17-24 January 2006) in the study site of Mae Chaem district was follow a pattern of contagious diffusion. They spread outward from a village of origin (Ban Rai) with high incidence to nearby villages, which related to the area of high population densities, within the urban and agricultural areas along the main course of Mae Chaem River.