Careful With that Bag o' Salad

Consumer Reports found that 39 percent of samples exceeded this level for total coliform, and 23 percent for Enterococcus. The tests did not find E. coli O157:H7, Listeria monocytogenes or Salmonella--sometimes deadly pathogens which can be found in greens, although it was not expected given the small sample size. According to Consumers Union, the goal was to investigate other markers of poor sanitation that should be used in the food safety management of produce.

This is from  the March 2010 issue of Consumer Reports and is available free online.

They are convenient and a good buy when you don't eat enough greens to justify whole heads of lettuce or bunches of spinach but they do have a risk. None of these greens found contaminated would have made you sick but it does show that they are not properly cleaned and protected from environmental contamination. The article goes on to recommend how you can reduce your risk when using these packaged greens.

• Buy packages far from their use-by date.
• Wash the greens even if the packages say "prewashed" or "triplewashed." Rinsing won't remove all bacteria but may remove residual soil.
• Prevent cross contamination of greens by keeping them away from raw meat and poultry. 

If you are going to use them then be smart about it. I buy the clam shells of spinach(when on sale) but I cook them and even then I wash them and spin them dry. I wash anything I buy from the store even if it says it is pre-washed.  At Whole Foods the 'spring mix' is often loose so that you can bag it yourself but know that I have seen them just opening the bagged variety and dumping it on the pile of loose greens so buying it 'loose' is not avoiding the danger.