National Public Radio: The illnesses started appearing in late March. Here and there, across the country, people were checking themselves in to hospitals, sick from toxic E. coli bacteria. At least 200 people got sick. Five of them died. Investigators quickly identified romaine lettuce as the source of the outbreak, but have had trouble pinpointing the cause for months. Now, the Food and Drug Administration has a theory for how E. coli ended up on that lettuce.