On August 21, 2004, a general practitioner in the Vendée region reported 15 cases of flu-like symptoms to the Departmental Directorate of Health and Social Affairs (DDASS) in his department; all of the patients had been staying on August 4 in the Vendée, in a mill that had been converted into a residence. The diagnosis of typhoid fever, initially made by the doctor, was quickly ruled out. An exploratory investigation conducted by the DDASS of Vendée and Loire-Atlantique initially failed to identify a common environmental or animal source. On September 8, a definitive diagnosis of tularemia was established through serological testing for 3 of the 15 patients. Given the similarity of symptoms among all patients, who had visited the same location on the same date, the case was classified as a cluster of tularemia. An epidemiological and environmental investigation was launched to confirm the diagnosis of tularemia, determine the extent of the outbreak, and identify a potential source of contamination in order to implement appropriate control measures. (Context excerpt)