An outbreak of gastrointestinal upset that affected several dozen guests who attended a conference at the Orlando World Center Marriott is under investigation by the Orange County Health Department, officials said Thursday.

The guests stayed at the hotel between June 29 and July 7 and have all gone home, said Gary Dybul, director of sales and marketing for the resort. Health officials said it was too early to tell whether the illness was caused by a virus or was foodborne.

Symptoms included nausea, vomiting and diarrhea and lasted on average from 24 to 48 hours, said Dain Weister, health department spokesman.

Most of those affected were adult guests, but a handful of children also fell ill as well as one employee, Weister said. Most symptoms were minor, but one person went to the emergency room for treatment and was released.