A 10K run was organized in southwestern France in early April 2017. Several dozens of runners had discomforts, some of them very serious faint. Early health care was provided by first aid workers on site. Fire and emergency Service and the local hospital activated their emergency response plan. The Regional Health Agency called on the local Poison Control Center (PCC) and the Regional office of the French National Agency for Public Health to investigate the outbreak. The purpose of the survey was to describe the event and to determine the causes of these discomforts, and the risk factors of their occurrence.

An exploratory survey was set up to describe the event. Telephone interviews were conducted with the race organizer, the first aid station director, paramedics and the local hospital. People transported to the hospital were asked about their consumption (water, food, doping substances, medication, etc.) before and during the race, their risk factors for hyperthermia, as well as their symptoms through an individual questionnaire. A telephone survey was conducted by an epidemiologist. Emergency and hospitalization reports as well as the results of biological and toxicological analyses were evaluated by a toxicologist from the regional PCC.

The running event gathered 4280 participants, including 70 dropouts. The event started at 6:30 PM. First participants arrived on site at 4:30 PM, which implied a 2-hour-wait under unusual heat for the season (27°C at 6 PM). The first aid station took care of 31 people during and after the event for severe dehydration and hypoglycemia, especially after the 7th and the 8th km A total of 17 people (2 women and 15 men, between 23 and 52 years old) were transported to the hospital, 15 of them for a medical consultation and 2 were hospitalized in intensive care. They all recovered; no deaths were reported. Individual risk factors could be investigated for 7 men who were transported to hospital, including the 2 admitted to intensive care. Of these, 2 were overweight, 1 reported chronic pathology (asthma). None had used alcohol or other psychoactive substances within 24hours of the race. It was the first participation to such an event for only one man. However, this man practiced running on a regular basis. Four runners spontaneously reported a lack of water or difficulties to access to the water, particularly at the 7th km. Eight hospitalization reports were sent to regional PCC. The clinical and biological analyses of these patients were consistent with heat stroke. Toxicology tests did not indicate any presence of toxic substances. For one of the patients, the consumption of a prescribed medication (corticoid) may have contributed to the occurrence of the heat stroke.

The investigation was consistent with heat stroke. Relatively hot conditions, prolonged exposure to heat before the race, limited access to water stations and some unclear waypoints may have been aggravating factors. A delay in preventive health care (rehydration–cooling) was also reported. These elements were taken into account by the organizers for the organization of the next races. The organization of a sport's events during a heat wave requires specific precautions to be taken by the organizers and by participants. Prompt medical assistance during the race is needed.