Health officials say 41 people reported getting sick in recent weeks after eating at the Nantucket Grill or attending an event catered by the restaurant.
The first illnesses were reported May 7.
Nantucket Grill released this statement in response to the outbreak:
"We strive to provide the highest quality service to our customers. We will continue our training to ensure that our staff is educated about proper food safety procedures. In the 50 years that the Sullivans have been in the restaurant business, this is the first time they have encountered anything like this.
Nantucket Grill has locations in Durham and Chapel Hill.
Inspectors have checked out all locations, but haven't been able to pinpoint the source of the virus.