Health officials in Las Vegas are investigating a norovirus outbreak connected to a youth football tournament that occurred there last week. The Southern Nevada Health District said it has not released a case count, but organizers of the tournament are saying that 90 to 100 children and parents have fallen ill. The health district has also not released information on the number of ill people who went to hospitals, said public information officer Jennifer Sizemore. Approximately 28 people are believed to have been hospitalized, according to CBS News. “The health district is investigating. We’re gathering information, issuing surveys to attendees, seeing if there’s a common source, if any,” Sizemore told Food Safety News, adding that it is often difficult to find the source in norovirus outbreaks. At least 18 people staying at the Rio All-Suite Hotel & Casino were reportedly taken to hospitals earlier in the week. The event, which was headquartered at the Rio, had about 7,000 attendees. Attendees staying at other hotels also became sick, according to tournament organizers. Food Safety News received a tip that two “seriously ill” patients were admitted to a hospital in Riverside, CA, after returning home from the tournament. Inquiries to the hospital had not been returned as of press time. Norovirus is highly contagious and can easily spread between people. Food may also become contaminated with the virus and infect those who eat it. Symptoms of norovirus include diarrhea, nausea and stomach cramps. It is often incorrectly referred to as the “24-hour flu.”