SIMI VALLEY (CBSLA.com) — The E. Coli outbreak at Chipotle restaurants is over, Centers For Disease Control officials said Monday, but the investigation did not pinpoint one single food or ingredient as the cause.

“The epidemiologic evidence collected during this investigation suggested that a common meal item or ingredient served at Chipotle Mexican Grill restaurants was a likely source of both outbreaks,” a CDC statement issued Monday said. But, “the investigation did not identify a specific food or ingredient linked to illness.”

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The last E. Coli case associated with Chipotle started on Dec. 1, according to the CDC.

Interviews of the people who had gotten sick showed that 52 reported eating at Chipotle in the week before their symptoms surfaced. However, health officials from Oregon and Washington who examined the foods eaten by both sick and healthy people at Chipotle could not identify any specific item or ingredient that could explain the outbreak.

Further testing of multiple food items collected from Chipotle restaurant locations did not identify the specific strain of E. coli that had sickened so many people, according to the CDC.

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Two outbreaks of E. Coli were investigated at Chipotle restaurants. The larger outbreak included 55 cases and 21 hospitalizations across 11 states and was first detected by public health officials in Washington and Oregon in late October 2015.

A second, smaller outbreak involved just five cases with one hospitalization in three states because of a different, rare strain of the disease. Those cases first began surfacing in November 2015.

Neither outbreak caused any deaths.

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The embattled restaurant chain touting its “Food With Integrity,” was also recently served with a federal grand jury subpoena over an outbreak of Norovirus at a Simi Valley location that sickened 19 people.