Most E. coli are harmless, but Shiga toxin-producing E. coli (STEC) can cause serious disease. FoodSafety.gov links STEC to undercooked ground beef, unpasteurized milk and juice, soft cheeses from raw milk, and raw produce.
Symptoms can include severe diarrhea (sometimes bloody), stomach pain, and vomiting. Some people develop hemolytic uremic syndrome (HUS), a serious kidney complication.
Cook ground beef thoroughly, avoid unpasteurized milk, and wash hands after handling raw foods.