Any veg that is harvested is done so by humans. One things human need to do is shit during the day. One thing farmers hate is installing any kind of plumbing in the fields so they bring portable toilets on trailers. Sometimes the toilets are broken or full and someone needs to shit real bad so they shit on the edge of the field where no one is looking. The poop is covered by dirt and tracked on shoes through the rows of veg.

This is how human waste gets on vegetables. Farmers don't have the right facilities to handle humans and waste ends up on the food.

It's a common problem on farms which don't provide adequate bathroom facilities for their laborers and/or don't allow a reasonable amount of time to use those facilities. Or to put it a different way: if your boss screams at you for being lazy and threatens your job every time you leave the field to use the toilet, you tend to just start shitting in the field.

probably not handwashing.