Harvard health officials announced yesterday that more than 12 cases of mysterious stomach illness, originally diagnosed two weekends ago as food poisoning contracted from a Freshman Union meal, were in fact caused by a virus.

George Weinert, deputy director of Harvard Environmental Health and Safety, said that after a week-long inquiry, investigators from his department concluded that the short-lived gastro-intestinal sicknesses were not connected with food problems in the Union.

"The investigation has resulted in the fact that it is not a food-borne problem," Weinert said. "Based on UHS analyses, it is a virus."

Health officials in both Boston and Cambridge said that they have not seen similar sickness trends in the larger community and that this is most likely an isolated Harvard event.

Benjamin Walcott, assistant director of Harvard Dining Services, said that the last known incident of food poisoning on campus occurred more than 10 years ago in one of the Quad dining halls. Walcott credits the dining halls' practice of not reusing food for the low incidence of contamination.

"The last food poisoning incident seems to me to have been 10 years ago or perhaps more," Walcott said. "Because our menu items are prepared for a specific meal and are not carried over [to the next meal], there is, in my opinion, less of an opportunity for a food-borne illness here than there might be in a restaurant," he said.

The range of symptoms experienced by the patients included high fever, nausea, abdominal cramps, diarrhea and vomiting, said Sholem Postel, chief of professional services at University Health Services (UHS). The epidemic ran for approximately 10 days, with symptoms lasting only one to two days, he said.

Postel said the coincidence of eight patients with similar symptoms arriving at UHS on the same Saturday morning could be explained by the mathematical concepts of a bell curve.

"If you look at a phenomenon in a community, it will be shaped something like a bell curve," Postel said. "That weekend just happened to be the peak of the curve," he said.