Impact of tourism on the epidemiology of influenza in the ski resorts of the French Alps

In France, the surveillance of influenza epidemics is carried out through a community-based surveillance network combining clinical and virological data. This surveillance is implemented in the Rhone-Alpes region, including the large ski resorts. In these resorts, numerous tourists are coming from France as well as from other European countries throughout the entire ski season. A specific network has been implemented in the ski resorts of the Alps (GROG-SKI) to analyse the circulation of influenza in these villages. Since winter 2001-2002, 11 GPs in seven resorts have been collecting virological specimens from patients presenting with acute respiratory infections, including both natives and visitors. During the last winter period, we compared the circulation of influenza in the GROG-SKI network with the circulation of influenza in the Rhone-Alpes region, with the exclusion of the departments of the Alps (Savoie and Haute-Savoie). Overall, from the 15th of December until the 15th of April, 105 samples were collected in the GROG-SKI network, compared with 495 in the other departments of the Rhone-Alpes region; influenza being detected in 34 (32.4%) and 187 (37.8%) specimens, respectively (p = 0.2). The peaks were observed at the same period, in mid-February, with the same shift from Influenza B to Influenza A viruses by the end of March. Within the Rhone-Alpes region, the influenza epidemic was observed at the same period of time in the ski resorts and in the remaining part of the region during winter 2002-2003; both surveillance yielding identical epidemic curves. This result suggests that the tourists coming to the ski resorts are exposed to the risk of developing influenza according to the epidemic status of the region, and that they have a minor impact on the epidemiology of influenza viruses in the ski resorts. (C) 2004 Published by Elsevier B.V.