Symptoms of gastroenteritis compatible with a food-borne outbreak started appearing among employees at the central headquarters of a “Bank” located in Beirut, Lebanon, on the evening of Monday 17 May 2004. Earlier on that day, many employees had had lunch at the bank cafeteria. All of those with signs and symptoms had eaten the main dish of chicken noodles au gratin served at the cafeteria on that day. The chicken noodle dish had been brought from the kitchen of a local catering company in 2 large serving containers. This catering company has an excellent reputation in Beirut and had been serving the Bank for more than a year with no previous problems reported.