Seven of the 15 people had to be hospitalized for dehydration due to vomiting and diarrhea.
Some of the 15 ate at a catered event, while a family of three people ordered carryout during the same time period.
Owner Tommy Bullock estimates his restaurant served at least 5,000 customers at catering events and at his restaurant around the same time the 15 customers became ill.
The Durham County Health Department says it is investigating the outbreak. But finding the source has been a bit of detective work for health inspectors who have visited Bullock's twice this week.
"We look at the individuals who have reported illness, we interview to find out what they ate if they are connecting to other people who have been sick," Gayle Harris with the Durham County Health Department said.
In a press release Tuesday afternoon, officials said early laboratory results suggest Salmonella as the cause of the illnesses, but further confirmation at the North Carolina State Laboratory is necessary.
There is at least one confirmed case and four probable cases at a local hospital.
Bullock tells ABC11 Eyewitness News he's cooperating with the health department's investigation. He says he believes the source of the illness may not be limited to his restaurant.
Officials say anyone who has not developed symptoms in the week following a meal from the restaurant, has very little risk of developing future illness. Customers who have eaten food from the restaurant since April 20 and have nausea, vomiting, diarrhea, abdominal pain and fever symptoms should contact their primary health care provider.
"If they've had any of these symptoms or illnesses we want them to give us a call," Harris said.
For any questions or to report a gastrointestinal illness in the past week associated with the restaurant, contact the Durham County Health Department at 919-560-7882.