An outbreak of E. coli traced back to Chipotle restaurants in Washington and Oregon has spread to six states.

According to CDC, new cases were found in Ohio, New York and California. A total of 45 people are reported to have been infected with the outbreak strain including the original patients in the Pacific Northwest and more recently Minnesota.

At this time, investigators say the evidence suggests a common meal item or ingredient served at Chipotle restaurants is likely the source of the outbreak. However, a specific source of the E. coli bacteria has yet to be found.

Of the 45 reported illnesses, 43 people reported eating at Chipotle in the week before getting sick. As a response to the outbreak, Chipotle closed 43 restaurants in the Seattle, WA and Portland, OR markets earlier this month. These restaurants were later reopened after a thorough cleaning.

The restaurant chain says it has taken aggressive steps to make sure its restaurants are as safe as possible. Specifically, the company conducted deep cleaning at the restaurants that have been linked to this incident, replacing ingredients in those restaurants, changing food preparation procedures, providing all necessary supply chain data to investigators and surveying employees to be sure none have had any symptoms of illness.

The company is also expanding testing of key ingredients, examining all of its food-safety procedures to find any opportunity for improvement and is working with food safety scientists to assess all of its food safety programs.

“We take this incident very seriously because the safety of our food and wellbeing of our customers is always our highest priority,” says Steve Ells, chairman and co-CEO of Chipotle. “We are committed to taking any and all necessary actions to make sure our food is as safe as possible and we are working diligently with the health agencies.”