B,
just because you might be getting paranoid doesn't mean somethings not right. After doing some reading-see below paste. It is broken down from the following site so it's not verbatim.
http://www.cdc.gov/ncidod/dbmd/diseaseinfo/escherichiacoli_g.htm#How is E. coli O157:H7 spread
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Because the organism lives in the intestines of healthy cattle, preventive measures on cattle farms, during meat processing, and during the growth, harvest and processing of produce are being investigated.
people have also become ill from eating contaminated bean sprouts or fresh leafy vegetables such as lettuce and spinach.
E. coli O157:H7 is one of hundreds of strains of the bacterium Escherichia coli. Although most strains are harmless, this strain produces a powerful toxin that can cause severe illness. E. coli O157:H7 has been found in the intestines of healthy cattle, deer, goats, and sheep.
Cattle manure is an important source of E. coli O157. Manure can contaminate the environment, including streams that flow through produce fields and are used for irrigation, pesticide application, or washing. Collaborative efforts are needed to decrease environmental contamination and improve the safety of produce.
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I wonder if someone is allowing cattle and other livestock to graze on the crops between replantings and the deficated soil is picking up the contaminants and transfering them to the new plants. Not to forget the runoff from adjacent fields. We all know we're supposed to wash veggies before eating however fast food places (IMO) don't have the time to do a thorough preparation and just take the lettuce and such out of the box and use it.
Since e coli is mainly a meat derived disease, there's not much else that contaminate veggies.