An E. coli outbreak that sickened 55 customers of Chipotle Mexican Grill Inc. and contributed to a sharp decline in traffic at its restaurants appears to be over, the U.S. Centers for Disease Control and Prevention said Monday.

Federal investigators said they couldn't identify a contaminated food or ingredient responsible for the illnesses, which occurred late last year in 11 states.

The CDC also said Monday that a smaller E. coli outbreak linked to Chipotle appears to be over. That outbreak, associated with a different strain of E. coli, sickened five people in three states.

Though evidence collected by investigators following the two outbreaks indicated that a common meal or ingredient served at Chipotle restaurants likely was responsible, health officials couldn't pinpoint a specific source, according to the CDC.

"We are pleased that the CDC has concluded its investigation, and we have offered our full cooperation throughout," Chipotle spokesman Chris Arnold said in a statement. "Over the past few months we have taken significant steps to improve the safety of all of the food we serve, and we are confident that the changes we have made mean that every item on our menu is delicious and safe."

Since the CDC's last update to the public on Dec. 21, two more people were reported ill, in Delaware and Kentucky, raising the number of cases in the larger outbreak from 53 to 55. according to the agency. The most-recent illness connected to that outbreak started on Dec. 1.

Chipotle shares were up at 4.9% to $475 in midday trading Monday. The stock jumped earlier in the session following a report by The Wall Street Journal on Sunday that the CDC was expected to soon declare the outbreak over.

Write to Jesse Newman at jesse.newman@wsj.com and Julie Jargon at julie.jargon@wsj.com

 

(END) Dow Jones Newswires

February 01, 2016 13:45 ET (18:45 GMT)

Copyright (c) 2016 Dow Jones & Company, Inc.
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