What is E. coli? Escherichia coli (E. coli) is a diverse group of bacteria that normally live harmlessly in the intestines of healthy people and animals. Most varieties are entirely benign or cause only brief bouts of diarrhea. However, certain mutated strains—most notably E. coli O157:H7 —produce a powerful toxin known as Shiga toxin. This specific strain can cause devastating illness, including severe abdominal cramps, violent bloody diarrhea, and vomiting. You may be exposed to these dangerous strains through contaminated water or food—especially raw vegetables, unpasteurized milk, and undercooked ground beef. Symptoms Symptoms typically begin 3 or 4 days after initial exposure to the bacteria, though the incubation period can range anywhere from 1 to 10 days. Common clinical signs include: Diarrhea: Often starts as mild and watery but can rapidly progress to severe and bloody. Abdominal Cr...