(CNN) — The cause of an E. coli outbreak linked to Chipotle restaurants in Washington and Oregon remains unknown, according to health officials from the Washington State Department of Health.
Tests of food samples from the restaurants found no traces of E. coli, the health department said Monday.
Nearly 25 food samples were taken from Chipotle locations in Oregon, which also found no E. coli. Results are still pending for a few samples.
This is not unusual as contaminated foods are sometimes consumed or thrown out before samples are taken, according to health officials.
To date, 42 people (27 in Washington and 15 in Oregon) have become ill from E. coli, according to the Centers for Disease Control and Prevention. Fourteen of those individuals have been 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.
Chipotle restaurants across Washington have remained closed as a precaution since the outbreak was identified. State health officials outlined the process the establishments will 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.
In Oregon six Chipotle locations in the Portland area have been closed. They will follow the same criteria for reopening as the Washington locations, according to Oregon health officials.
Last week the chairman and co-CEO of Chipotle, Steve Ells, said in a statement, “The safety of our customers and integrity of our food supply has always been our highest priority.”
There is one case of the same strain and DNA fingerprint of E. coli in Minnesota, but that person had not eaten at a Chipotle within the week before symptoms began, therefore health officials believe this is an unrelated case. The CDC is unaware of any cases in other states.
State and local health officials continue to work with federal health officials to investigate this outbreak.