Relative risk for influenza like illness in French Hajj pilgrims compared to non-Hajj attending controls during the 2009 influenza pandemic.

The incidence of influenza like illness was evaluated in a cohort of 273 French pilgrims participating to the Hajj 2009 and compared to non-Hajj attending control data from Sentinel System, a nationwide network of French general practitioners who report, in real time, the number of medical visits for influenza like illness. Cases of influenza like illness in pilgrims were observed during weeks 45-50, 2009, with a mean incidence of 1211 cases per 100,000 pilgrims, compared to 520 in controls during the same period. The highest incidence in pilgrims was observed during week 48, corresponding to the Hajj ritual dates.