**2. History**

Since the beginning of August 1982 specimens obtained from four patients located in the United States of America, who were suffering from an unusual bloody diarrheal illness started suddenly with abdominal pain within 24 hours followed by watery diarrhea, led to identification of *Escherichia coli* serotype O157:H7. All patients recovered within 7 days.

By further examination of stool samples from different cases of this type of diarrheal illness which nowadays designated as "hemorrhagic colitis," for the first time CDC associated the 1993 large outbreak with undercooked hamburgers served at fast-food chain restaurants in Oregon and Michigan. Hemorrhagic colitis is characterized by severe abdominal pain, grossly bloody diarrhea, and even fever [3].

*E. coli* O157:H7 is the most commonly identified member of STEC and is becoming as a best-known emerging pathogen in the United States causing foodborne diseases [4, 5].

However, experiences have established a diversity of sources for *E. coli* O157:H7, including apple juice and cider, vegetables such as lettuce, raw milk, and processed foods such as salami [6].
