The whole point of buying prewashed salad greens in a bag or plastic container is to make dinner and meal prep a cinch. Some of them are "triple washed" — I don't even do that at home! Unfortunately, that prewashed organic spinach or arugula may not be all that clean or safe to eat.
Registered dietitian Leslie Langevin, MS, author of The Anti-Inflammatory Kitchen Cookbook [1], recommended washing all produce, including those with peels you don't eat like avocados [2] to get rid of germs, bacteria, and pesticides. She also said, "I recommend rewashing packaged greens that have been washed. I have found dirt and even bugs before in my prewashed greens, as I am sure lots of other people have found, too." Um, eww!
Even if you're OK with a little soil or caterpillars mixed in with your mesclun, you're probably not OK with E. coli, salmonella, or listeria. The Centres For Disease Control [3] (CDC) follows what the FDA recommends [4], which is to wash and dry all raw fruits and veggies before consuming. As for prewashed produce that says it's "ready to eat," including greens, carrots, and sprouts, the FDA said "you can use the produce without further washing," but "if you choose to wash produce marked as 'prewashed' or 'ready-to-eat,' be sure that it does not come in contact with unclean surfaces or utensils. This will help to avoid cross contamination."
The FDA added that, "Washing may reduce bacteria that may be present, but it will not eliminate it." So if you're worried about the ickies on your veggies, sounds like you can't go wrong with a little extra washing. Just make sure your hands are washed before handling any produce and that your utensils and cutting board are also clean. Cut away any damaged or bruised areas, and if a fruit or veggie looks or smells funky, it's best to throw it out.