In the spring of 2013 twenty six cases of E. coli O26 infections were reported by 13 states: Illinois (6), Minnesota (5), Wisconsin (3), Michigan (2), California (2) and Kentucky, Missouri, Mississippi, New Jersey, new York, Ohio, Washington and West Virginia, 1 case each. Estimated and known illness onset dates ranged from April 21 to May 30. Five (19%) cases were hospitalized and none died.

Of the cases with exposure data available, 10 (71%) of 14 reported eating at 1 of 7 Restaurant Chain "X" locations in the week prior to illness. Eighteen (82%) of 22 cases reported that they maybe ate at a Restaurant Chain "X" location in the week before illness onset. The majority of cases reporting Chain "X" exposure consumed ground beef and iceberg lettuce at the restaurant. Several of the cases also reported ground beef and pre-packaged iceberg lettuce exposures at home and at other fast food restaurants.

According to the CDC, Restaurant Chain "X" performed an internal traceback investigation of their iceberg lettuce supply to the 7 restaurants reported by cases. The stores were supplied by eight different growers via two suppliers. Using modeling, there were four scenarios where all seven restaurants could have received the same lot of shredded iceberg lettuce. However, Restaurant Chain "X" concluded that it was unlikely that any of these scenarios actually occurred since the shelf-life of iceberg lettuce is short and the product is quickly moved through restaurant locations.

Investigators concluded that this was an outbreak of E. coli O26 probably associated with consumption of iceberg lettuce. The specific retail and/or restaurant sources could not be definitely determined.