The Centers for Disease Control and Prevention has declared that two E. coli outbreaks linked to Chipotle Mexican Grill Inc. “appear to be over,” but the agency has not identified a food source for the outbreaks.

“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,” the agency said. “When a restaurant serves foods with several ingredients that are mixed or cooked together and then used in multiple menu items, it can be more difficult for epidemiologic studies to identity [sic] the specific ingredient that is contaminated.”

Meanwhile, Chipotle faces a joint investigation by the U.S. Food and Drug Administration and U.S. Department of Justice into a 2015 norovirus outbreak in one of its California restaurants. The company has reportedly been served an additional subpoena requiring it to produce documents on company-wide food safety measures dating from 2013. Additional details about the probe appear in Issue 589 of this Update. See Reuters, February 2, 2016.