I posted a link the other day to a piece about a Consumer Report's study that revealed, much to many people's collective disgust, the relatively high levels of microbial contamination in packaged and "pre-washed" salads. For most non-biologists, myself included, the study's discussion of "coliforms and other bacteria, including enterococcus, that are reliable indicators of fecal contamination and poor sanitation" suggested a variety of mental images I'd rather not associate with dinner.
Which is why this article from Food Safety News is so useful. Dr. Trevor Suslow, a "cooperative extension research specialist in postharvest quality and safety in the Department of Plant Sciences at the University of California at Davis," provides a primer in the terminology and science of salad safety, and basically concludes that while we might not like that our salad is full of coliforms, these microbes are generally and basically benign.
Suslow says that he personally does not re-wash packaged salads. He also offers this practical advice for consumers of these products:
If one chooses to take advantage of the convenience and diversity of greens available in sensible serving portions or as complete salad meals, it is always best to look at the Best if Consumed By dating and take notice of the display case arrangement. Bags should be vertical in a row, not laid one on top of the other in stacks. Clamshell containers are displayed in various stacking or slanted row patterns which allow generous space for airflow.