On December 24, 2003, the InVS was notified by Ifremer of foodborne illness outbreaks attributed to the consumption of oysters in the Vendée and Seine-Maritime departments. On the same day, the DGAl contacted the InVS to obtain epidemiological information on these outbreaks, which would help guide control measures (including potential product recalls). These foodborne illness outbreaks had occurred among the families of employees at Company I in Fontenay-le-Comte (85) and its subsidiary C in Le Trait, Seine-Maritime (76). One hundred thirty-five baskets of oysters from a production site on the Île de Ré (Company B) had been distributed to these two companies on December 19. About ten cases of acute gastroenteritis among families who had consumed oysters over the weekend of December 20–21 were reported to the works council, which then issued a warning by contacting all families who had received oysters and advising them not to eat them. Some of the affected families nevertheless served these oysters despite the warning. (Introduction)