People with E. coli infection usually have a sudden onset of diarrhea, often with visible blood, and stomach cramps. Most people have no fever or a very low-grade fever. A stool sample tested specifically for E. coli is the best way to determine if someone is infected.
Taking antibiotics or over-the-counter anti-diarrhea medicines can make the infection worse. Call your doctor if you experience sudden diarrhea with blood in it.