Specimens from 10 patients were confirmed to be a shiga-toxin producing form of E. coli, a type of enterohemorrhagic bacteria that can cause illness ranging from mild intestinal disease to severe kidney complications, state epidemiologist Dr. Kristy Bradley said.
"These toxins are responsible for the very severe disease that we are seeing in many persons sickened by this outbreak," she said.
Also Wednesday, Bradley directly linked the outbreak to the Country Cottage restaurant in Locust Grove.
State health officials had noted Monday that most of the sickened patients had eaten there.
Bradley said Wednesday that some of the people infected with the bacteria had not eaten at the restaurant but likely were infected by others who had eaten there.
"We know that something at the restaurant led to this foodborne illness outbreak," Bradley added.
A Tulsa World call to Country Cottage owners Dale and Linda Moore was not returned by publication time.
The Moore family said in a statement, though, that the Country Cottage will remain closed indefinitely while the Health Department continues its investigation into the source of the contamination.
In a written statement, the Moores said, "While we feel somewhat relieved in knowing what the cause is, it is difficult to put into words how heartbroken and distraught we are for our entire community, including our close friends and neighbors who are sick or those who have relatives who are sick."
The Moores declined to reveal the suppliers for their meat, produce and other food products.
However, Bradley said Wednesday that "we think it's much less likely that it was a contaminated food item and more likely cross-contamination."
In other words, state health officials think the source likely was not food that came contaminated from a supplier but something that became contaminated after it was in the restaurant.
Bradley also said she believes that officials are "zeroing in on the source" of contamination and could know within the next day or two.
She said the potential for spreading the diarrheal illness to close contacts or household members is high.
"Only a few bacteria can make a person sick, and these bacteria can be easily transmitted person-to-person if infected persons do not wash their hands after using the toilet or changing diapers," Bradley said.
She urged physicians treating patients with the gastrointestinal illness to refrain from using antibiotics and anti-diarrheal medication.
Such treatments could worsen the illness by releasing the toxins further into the system instead of allowing them to pass through the patient's system.
Bradley said state officials sent the specimens to the federal Centers for Disease Control and Prevention for help in determining specifically what kind of E. coli was present because it "did not match anything we have had previously in Oklahoma."
The incubation period from the time of exposure to this E. coli strain can be as short as two days or as long as 10 days, she said, adding that "conceivably we could continue to see new cases until the end of the month."
"I wish I could say the outbreak is coming to an end," she said, but information from hospitals indicates that new patients are continuing to come in.
"While we cannot predict at this point how long this outbreak will continue, we believe we have prevented the spread of any further cases that may have been connected to eating at Country Cottage at Locust Grove," Bradley said.
The town of Locust Grove had tested its water supply to make sure it was not the source of contamination.
Mayor Shawn Bates said late Wednesday that the samples tested came back free of E. coli or any other dangerous bacteria.
The Oklahoma Department of Environmental Quality also tested water samples this week, but the results of those tests had not come back by Wednesday.