The unusual case could be of interest to the federal officials.
The state Health Department has asked federal health investigators to come to Oklahoma and aid in the investigation into the E. coli outbreak that sickened hundreds of people and killed a man in northeastern Oklahoma.
In its Friday situation update, the Oklahoma State Department of Health announced that it has invited U.S. Centers for Disease Control and Prevention officials from its foodborne and diarrheal diseases branch.
State epidemiologist Dr. Kristy Bradley said, "This outbreak is of great interest to CDC because it will add to knowledge on the range of disease that the E. coli O111 organism can cause."
At least 206 people have been sickened and one man has died as a result of the outbreak of E. coli O111, a rare and virulent strain of the infection.
Federal investigators will conduct medical reviews to look at acute symptoms and complications of those who became sick from the E. coli O111 infection. They will also help state investigators with telephone interviews with other people who ate at Country Cottage in Locust Grove, which has been the focus of the state's investigation.
"In our efforts to establish if there is an association with particular food items and illness, we will be interviewing more persons to find those who ate at the Country Cottage and did not become ill," Bradley said.
Investigators have identified at least 320 more people who have not been interviewed who ate at the Country Cottage between Aug. 15 and Aug. 17. Most of those who became ill ate at the restaurant on those three days, she said.
Anna and Wilburn Faught of Claremore are just two of many people who ate at the Country Cottage during the third week of August and didn't get sick.
"My husband and I just like the food good. And it was always clean," said Anna Faught, who ate there with her husband for their 58th anniversary Aug. 19.
She said knows of other people who ate at the restaurant around that time and didn't get sick.
"I don't think it was the restaurant," Faught said. "They're blackballing that place."
She said the restaurant was always crowded, so the food on the buffet steam tables never had time to go bad or get cold.
"I don't know the owners, but I know they always strived to make a pleasant experience and serve good food," Faught said. "I wouldn't hesitate to go back and eat if they opened up tomorrow."
Bradley said such a large investigation requires more information about those who didn't get sick after eating at the Country Cottage restaurant, as well as those who did.
"We've determined that our statistical database does not adequately represent those who ate at the Country Cottage but did not become ill," she said.
The additional people will be contacted this weekend to see whether they can remember what they ate and if they got sick afterward, Bradley said.
"This information is necessary so that we can make the distinction between what might have been a popular food choice versus a valid association with illness," she said.