Stéphanie Vandentorren, Sylvia Medina, Mathilde Pascal, Adeline Maulpoix, and Martine Ledrans are with the Department of Environmental Health, Institut de Veille Sanitaire, Saint Maurice, France. Florence Suzan is with the Department of Chronic Diseases, Institut de Veille Sanitaire. Jean-Claude Cohen is with the National Weather Service (Météo France).