There is alot of this happening on the spinach E.Coli threads, some are even suggesting that people wash the spinach in a bleach/water mixture to kill the e.coli and that it should be safe to eat raw after this is done.
The problem is the FDA is starting to think that the E.Coli has actually enter into the inside of the plant through the roots or that it has entered through the cut end of the stems and traveled up through the leaf veins during the washing process.
Cooking raw spinach at 160F degrees will kill the e.coli
Here is good article about how e.coli could be getting into leafy greens.
http://www.msnbc.msn.com/id/12536902/
Here is a small snippet... (this is only one possibility)
Scientists believe E.coli bacteria might have been absorbed by the lettuce plant’s root system. If that happens, washing the lettuce won’t do any good—the E.coli is already growing inside.