Résumé
Drastic environmental changes have occurred in Thailand during the twentieth century, along with the population growth and consecutive agricultural development consequently threatening the ecosystems. Infrastructures, and especially water reservoirs, were built to increase and improve the agricultural production. These changes have modified irreversibly the biotopes and, above all, the hydrographical network and water quality. In an effort to assess and monitor their consequences on human health, a health Geographic Information System was developed in Phrae province, North Thailand, focusing on the Mae Thang watershed, its reservoir and irrigated area downstream. In partnership with Phrae provincial Public Health Office, all patients' cases from 78 different pathologies, reported in Phrae rural areas from 1997 to 2004, were integrated and incidences were calculated among all the 693 villages, where patients and families live. Health infrastructures were also localized to assess the health offer, access, and recourse. Overall higher prevalence was recorded in Mae Thang study area as compared to the whole province, especially for infectious diseases that could be linked to water quality, as well as for upstream villages compared to those downstream. Marked geographical heterogeneity in disease prevalence between villages showed the importance of the choice of the study scale and the need for a public health survey at the village level to answer the hypotheses raised by the present observations.