A 4-year old girl presents at the emergency room with bloody…

A 4-year old girl presents at the emergency room with bloody diarrhea, fever and vomiting.  The child’s mother reports that the child has had these symptoms for about 24 hours and she has not passed any urine for about 12 hours.  The child is enrolled in a day care center and the group had recently made a field trip to a fast food place to learn about different jobs.  The children had a lunch of hamburger, fries, and cola after meeting with different workers.  This field trip was four days earlier on Friday.  The child showed physical signs of dehydration.  Blood samples showed evidence of greatly reduced kidney function and lysed red blood cells.  The most likely cause: