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Getty Images Q: Every time I hear about a deadly E. coli outbreak, I wonder: How do I tell the difference between harmless food poisoning and the life-threatening kind?

A: While a bout of food poisoning totally sucks, most of the time the vomiting, diarrhea, aches, and fever will go away on their own in a couple of days. But in rare situations, a more virulent pathogen—such as certain strains of E. coli bacteria that produce a poison called Shiga toxin—can lead to severe, life-threatening dehydration or kidney failure.

If you have diarrhea along with a fever of 101 degrees or higher; if you feel very thirsty, dizzy, or light-headed; or if you have diarrhea that persists for more than three days, see a doctor. Head straight to the ER if you have a lot of blood in your stool or a pounding or skipping heart, or if you think you got sick from eating poisonous mushrooms, bad shellfish, or a contaminated canned item (toxins from these foods can have especially serious consequences).