The Maricopa County Department of Public Health (MCDPH)’s report of its investigation of an Escherichia coli O157:H7 outbreak in which 94 ill persons were identified was released today.

According to the report, the source of the outbreak was traced to a single location of Federico’s Mexican Restaurant chain located at 13132 W. Camelback Rd., Litchfield Park, with exposure dates occurring from July 18-30, 2013. A case-control study of 180 persons was performed, and environmental samples were collected on multiple dates.

The findings from the environmental samples and the case-control study both implicated contaminated lettuce as a probable source of the outbreak and vehicle for the E. coli that caused illness.  Midwest Beef supplied beef and produce to Federico’s Mexican Restaurant.

The report further found:

It is notable that the food supplier that provides produce to this restaurant also provides food to other Federico’s locations in Phoenix, as well as other food establishments in the valley. No confirmed cases of illness were recorded from other local restaurants. This point source exposure could have occurred due to contamination at any one of several levels. It could have occurred at the restaurant from an ill food handler, although no employee illnesses were reported from the restaurant during the month of July and this would be a large number of cases to be contracted from a single ill food handler. Cross contamination from another contaminated food source at the restaurant – such as beef, for example – is also a possibility. It is also possible that this restaurant received a small, highly contaminated batch of lettuce that did not go to any other facilities.