Infections in the digestive tract are due to multiple organism, which cause different syndromes. Escherichia coli O157:H7, already identified as a human pathogen in 1982, has been recognised as a major public health issue, being responsible for sporadic and epidemic cases of haemorrhagic colitis, often associated, in children and elderly, with the haemolytic uraemic syndrome. E. coli O157:H7 infection may occur everywhere, but is more frequent in North Europe, Canada, USA, Argentina and Japan, with annual incidence rates of 8 per 100,000 population. In Italy until 1997 the Italian National Institute of Health has identified 196 cases of haemolytic uraemic syndrome, in addition, an outbreak caused by E. coli O157:H7 occurred in 1993. In Italy the incidence of the haemolytic uraemic syndrome is 4-5 times lower than in Great Britain, Germany and other European countries. E. coli infection is more frequently associated with the ingestion of food from bovine and sheep origin and with infected water. The clinical spectrum includes an asymptomatic infection, non bloody diarrhoea, haemorrhagic colitis, haemolytic uraemic syndrome. When the E. coli infection is suspected, it is necessary to isolate the bacterium in a specialised laboratory. Treatment is essentially supportive in order to control anaemia and to maintain an adequate fluid and electrolyte balance, if necessary with the use of dialysis. The use of antimicrobial agents is currently under debate as there are controversial data on the risk of developing haemolytic uraemic syndrome.