After three days, however, health authorities have barely a clue to what caused hundreds of students to develop flu-like symptoms.

Food poisoning has still not been ruled out, although city officials found the Union clean from bacterial infection and ruled out water infection. The kitchen first-year dining hall will begin preparing meals today.

At first, Director of Dining Services Michael P. Berry thought the outbreak might be food poisoning.

"When I walked into University Health Services Tuesday night," he said, "my first thought was that this was food poisoning... every food handler's nightmare."

As the week progressed, however, Berry and investigators found the outbreak "more symptomatic of viral infection."

One key reason for that suspicion is that UHS staff who treated students were coming down with the same symptoms, while dining hall workers remained healthy. In addition, the epidemic was not limited to those who ate in the Union. Some of the ill came from upper class houses.

Still, it is possible that the virus was carried in the food. Such viral food poisoning is not common as bacterial poisoning, but it does occur.

Between 1983 and 1987, the Centers for Disease Control in Atlanta found 50,283 cases of bacterial food poisoning and only 2,790 cases of viral food poisoning.

Tun-Hou Lee, associate professor of virology in the School of Public Health, yesterday offered one possible scenario which might explain the mystery.

"It is possible that if some of the raw food bought by University food services was contaminated, this food could have been served in all the houses," Lee said. "In the Union, where there are more students being served, many more would have been effected."

Lee's suggestion does not necessarily explain why at least of one of the sick students had not eaten University food at all.

A first-year in Thayer Hall says she had only a bagel and some water in the Union Tuesday morning, and didn't eat University food again until Thursday. Nevertheless, she experienced fever, chills and nausea Wednesday night.

"That's just one of the many interesting things about this case," said University spokesperson Joe Wrinn. "The only answer is to collect a lot of data. They're going to mesh biological testing with surveys."

A survey passed out to all those who checked into UHS or told their proctors that they felt ill asked for a complete description of the food that the students have eaten since last Saturday night. The survey also asked students to detail their symptoms.

"236 surveys were completed by [Thursday] morning, hundreds more were handed in that afternoon, and I assume there are a couple hundred more in the proctor network," Wrinn said.