Escherichia coli (E. coli) are bacteria that normally live in the intestines of healthy
people and animals, primarily cattle.Most strains of this bacteria are harmless. E. coli
0157:H7 is a specific strain of E. coli that causes illness.It was first recognized as a
cause of illness during an outbreak of hemorrhagic colitis (severe bloody diarrhea) in
1982. The cause of that outbreak was traced to hamburgers contaminated with E. coli
0157:H7 bacteria.