More than 550 people who attended the P.E.I. International Shellfish Festival last weekend reported getting sick, according to the province's Chief Public Health Officer.

"This is the biggest gastrointestinal illness outbreak we have on record," Dr. Heather Morrison told CBC News on Friday.

Stool samples taken from people who ate food at the festival have tested positive for norovirus, Morrison said.

"That makes sense to us given all the information that we have."