Preliminary survey results in Washington state show about 229 reported illnesses during or after the Feb. 4 state high school cheerleading tournament in Everett.
Norovirus is responsible for the outbreak, the Snohomish County Health District reports.
Symptoms include vomiting and diarrhea, and while most people have recovered, at least 33 attendees have reported seeking medical treatment.
The state health department is leading the disease investigation, working with local health partners and the event sponsor, the Washington Interscholastic Activities Association (WIAA).
As part of the investigation, questionnaires were sent to participants and their families and stool samples are being collected for testing at the state Public Health Laboratories. People who attended the event and have severe symptoms are advised to contact a health care provider.
According to the WIAA, more than 3,000 people attended the event and more than 1,000 competed in the State Cheerleading and Salute to Spirit in cheer and dance/drill.