Health officials say the number of cases of E. coli linked to Chipotle restaurants in the Northwest has increased to 37. Of those, 12 people have been hospitalized.
Tuesday, Oregon health officials increased the number of confirmed cases in the state to 12.
Oregon State Health Officer Dr. Katrina Hedburg said most of the cases are in the Portland metro area, but people in Columbia, Benton and Deschutes counties have also reported symptoms.
"We're still trying to figure out whether all of these cases have eaten at Chipotle restaurants, and if Chipotle restaurants in other parts of the state are also associated with cases," she said.
Chipotle restaurants in Washington have also been linked to the E. coli outbreak. At least 25 people have been sickened there, with nine hospitalized due to the outbreak.
Health officials have identified the specific microorganism responsible for the E. coli outbreak as Shiga toxin E. coli 026.
Dr. Hedburg said it's not as severe as other types of E. coli.
She said health agencies are relying on the company and the U.S. Food and Drug Administration to help trace the source of E. coli.
"One of the problems that we have with a restaurant like Chipotle is that people go there to eat fresh Mexican food, and so people eat many of the same items when they go," she said.
She said whatever the source is could have gone to stores and restaurants other than Chipotle.
The restaurant chain has temporarily closed 43 restaurants in the two states while health officials work to determine the specific cause of the outbreak.
Health officials are currently developing guidelines for the company before reopening the stores.
"The real key in this is to try to figure out what food in the distribution pattern caused this and to stop that," Hedburg said. "We don't yet know the answer to that."
Chipotle has declined interview requests.
However in a statement Tuesday, Chipotle said it's sanitizing its restaurants in the region. In addition to replacing the food at all of it's closed stores, the company said it's performing its own testing of suspected food at its distribution centers.
The company said it's cooperating with the bi-state health investigation.
"If there are opportunities to do better, we will push ourselves to find them and enhance our already high standards for food safety," Steve Ells, chairman and co-CEO of Chipotle said in a statement.
"Our deepest sympathies go out to those who have been affected by this situation,” he said.
The company also announced it hired two food safety firms to help improve practices.
Dr. Paul Ceislak, medical director for communicable diseases at the Oregon Health Authority, said the restaurant chain has been cooperative.
"The company has been a model of cooperation in terms of giving us information that we need to try and do the investigation, and in terms of closing the restaurants right away," he said.
Ceislak said it's unlikely the food was contaminated at individual restaurants.
"It probably occurred at the farm with a produce item, possibly somewhere along the distribution chain," he said. "But I think the most likely thing is at the farm."