Because of the symptoms, Swanson thought it might be an outbreak of E.coli 0157 bacteria. E.coli comes from animal or, sometimes, human feces and is usually associated with undercooked ground beef. But health officials found the victims hadn’t eaten ground beef --- but they all had eaten something that you might never suspect of giving you food poisoning—bag salad.

It was Roi Dahl’s leftover lettuce that cracked the case. At the lab, scientists showed us how they were able to extract and isolate E.coli 0157 in the lettuce, then, using DNA markers, they compared it to the strain of E.coli that sickened Dahl, Amber Brister and the others. It was a perfect match.