Health officials said more than 60 people fell ill after attending a medical convention, with several reporting symptoms as they prepared to leave on flights from Washington.

Many of the victims came forward Friday, the day after attending the meeting Thursday at the Gaylord National Resort and Convention Center in Oxon Hill, Md.

Staff members of the Prince George’s County health department interviewed resort workers and inspected the center to determine what caused the illness. A private company has already started cleaning.