While there have been a few outbreaks of E coli from bagged greens, generally they are safe to eat. Pay attention to the expiration date on the bags. Also, even though the greens are washed before packaging, it does not hurt to wash them again. Bagged greens are an easy way to work more salads into your diet.
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Those watchdogs over at Consumers Union inform us that bagged salads are often contaminated with disgusting animal fecal bacteria. Investigators analyzed 208 packaged greens and discovered that 39% had odious bacterial contamination at levels nutrition experts consider unacceptable. Even the "prewashed" or "triple-washed" had evidence of bacteria, and those containing spinach fared the worst. The results were consistent among larger and smaller brands, bagged and clamshell. And being labeled organic made no difference.
The takeaway: Bagged salads can be convenient, but you must wash the greens thoroughly before using. Investigators found that those tested six or more days before the "use-by date" had lower levels of nasty bacteria.