One of the reasons animal foods are the leading culprits is that most foodborne pathogens are fecal pathogens. Because plants don’t poop, the E. coli you may get from spinach didn’t actually originate in the spinach; E. coli is an intestinal pathogen, and spinach doesn’t have intestines. The application of manure to crops has been found to increase the odds of E. coli contamination by more than fiftyfold.
