Anyone who eats raw sprouts, or lightly cooked mung bean sprouts, is at risk for exposure to E. coli or Salmonella bacteria. Seeds need a dark and moist environment to sprout, so the sprouting process provides ideal conditions for bacteria to grow.
It's a toss up because sprouts are really healthy for you though. They are a living food, so even after you refrigerate them, they will continue to grow slowly and their vitamin content will actually increase. Sprouts are one of the most complete and nutritional of all foods that exist - rich with vitamins, minerals, proteins, and enzymes.
If you buy them, choose crisp-looking sprouts with the buds attached - avoid musty-smelling, dark or slimy-looking sprouts. If you keep them in the fridge too long, because their roots stay moist, they can get moldy, so try to eat them right away.
Fit's Tips: Since you never know how old sprouts are when you buy them at the store, you could always grow your own. Buy your seeds and sprouters at sproutpeople.com. Unfortunately, this doesn't cut your risk because the seeds themselves could be contaminated.