Tests of food samples taken from the Washington state restaurants found no traces of E. coli, the health department said Monday.
And tests on nearly 25 food samples from Chipotle locations in Oregon also found no E. coli
. Results are still pending for a few samples.
Health officials said the findings are not unusual, because sometimes the contaminated foods are consumed or thrown out before samples are taken.
Test results from surfaces and equipment in the restaurants also showed no E. coli, according to a statement from Chipotle.
"To date, Chipotle has received nearly 900 test results, all of which showed no E. coli," the restaurant chain said.
As many as 42 people -- 27 in Washington and 15 in Oregon -- became ill with E. coli, according to the Centers for Disease Control and Prevention.
Fourteen of those sickened were hospitalized. Most of them reported eating at Chipotle locations before becoming ill.
Symptoms, which include diarrhea and abdominal pain, usually begin two to eight days after a person has been exposed to the bacteria and resolve within a week. Some cases are severe and patients can develop hemolytic uremic syndrome, or HUS, which is a type of kidney failure. There have been no cases of HUS or deaths from this outbreak.
The most recent illness was reported on October 24.
In a voluntary move by the company, Chipotle restaurants across Washington and Oregon have remained closed as a precaution since the outbreak was identified. State health officials outlined the steps the 43 closed establishments must go through before reopening. They include disposing of all food items, sanitizing each facility and bringing in all new food. Menu items identified as high risk will be tested before being sent to restaurants, and all fresh produce will be carefully rinsed and sanitized. In addition, county food safety inspectors will confirm these steps have been taken at each location.
Chipotle says its restaurants will be reopening in the coming days.
"The safety of our customers and integrity of our food supply has always been our highest priority," Steve Ells, chairman and co-CEO of Chipotle, said in a statement. "If there are any opportunities for us to do better in any facet of our sourcing or food handling -- from the farms to our restaurants -- we will find them. We are sorry to those affected by this situation, and it is our greatest priority to ensure that we go above and beyond to make certain that we find any opportunity to do better in any area of food safety."
A case of E. coli in Minnesota -- with the same strain and DNA fingerprint of the cases in the Northwest -- appears to be unrelated to the Washington and Oregon cases, health officials believe, because the person had not eaten at a Chipotle within the week before symptoms began. The CDC is not aware of any cases in other states.
State and local health officials continue to work with federal health officials to investigate this outbreak.