<i>Escherichia coli (E. coli)</i> are bacteria normally found in the environment, food, and intestines of people and animals. Most strains are harmless however some strains can produce toxins that cause diarrhea, urinary tract infections, respiratory disease, and other illnesses. Transmission is generally foodborne and the strain E. coli O157:H7 which produces Shiga toxin is responsible for the majority of foodborne outbreaks. Diagnosis is usually by serotype-specific enzyme immunoassays that detect E. coli O157 directly from stool samples. Other diagnostic tests include PCR and cytotoxicity testing.