Abstract
The \"Grand Raid de la Réunion\" is one of the hardest ultra trails in the world. This endurance running race has consequences on health''s runners. We used syndromic surveillance to estimate the health impact of this sporting event on the Emergency Departments (ED) of Reunion Island. During the race''s period, a global increase of the ED visits all causes was observed. The syndromic surveillance system detected a significant ED visits'' increase for hydro-electrolytic disorders. These results highlight the usefulness of syndromic surveillance to estimate the impact on health of a mass gathering on a sporting event of great magnitude.