Bean sprouts should be eaten fresh and are not harmful unless they have gone wrong. If they feel slimy or mushy, you can throw them away. They can also be contaminated by water and compost. Even if they look good, they should be thoroughly cleaned before eating. Otherwise, they could have E. coli or other bacteria growing in the water. It would help if you always bought your sprouts from a reliable source to avoid foodborne illnesses.
Generally, bean sprouts will have a spicy, sour, or unusual smell.