UMR CNRS 8586 PRODIG
2 rue Valette
Université Paris 1 Panthéon-Sorbonne/UMR CNRS 8185 ENeC
Institut de Géographie
191 rue Saint Jacques
Twenty-two years of epidemiological data about influenza like illness activity in France from the Sentinelles network were used to analyse the weather conditions observed before the onset of seasonal influenza epidemics (data from Météo-France, the French weather surveillance network). A first exploratory step showed systematic drops in both minimum and maximum temperatures in the weeks before the epidemic started. The subsequent simultaneous analysis of all meteorological parameters showed that the start of epidemics was associated with two types of weather: the first characterized by an average minimum temperature of 5.5̊ C associated with low pressure, a zonal flow, cloudiness and rain; the second (more frequent) is colder (average minimum temperatures of 0.5̊ C) and associated with higher pressure and a very meridional flow. Cold weather seems to be a necessary but not sufficient condition for triggering seasonal influenza epidemics outbreaks. The integration of meteorological parameters in the future should improve the forecasting of seasonal influenza epidemic outbreaks.