Also, children with a severely weakened immune system are at risk for more serious disease. Symptoms may be more severe and could lead to serious illness. Most strains of E. coli are harmless and live in the intestines of healthy humans and animals. E. coli, however, produces a powerful toxin that can cause a severe infection. An estimated 73,000 cases of E. coli infection occur in the United States each year.
Infection often leads to bloody diarrhea.
Transmission Most E. coli illness has been associated with eating undercooked, contaminated ground beef. E. coli bacteria live in the intestines of healthy cattle and, although the number of organisms required to cause disease is not known, it is suspected to be very small. Meat becomes contaminated during slaughter, and organisms can be thoroughly mixed into beef when it is ground. Contaminated beef looks and smells normal. Bacteria present on a cow's udders, or on equipment, may get into raw milk causing the infection.