The Center for Food Safety in Georgia says that lettuce is probably originally contaminated in the field with polluted irrigation water or animal manures.

They found that E. coli cells favor the cut edges of lettuce. "The edges of cut lettuce pieces had tremendous numbers of attached E. coli cells. The bruised areas did, too."

So wash it again and trim any bruises and cut edges.

They didn't recommend using bleach on the food.

Sue