Most E.coli that are found in the intestine are harmless. However, E.coli O157 produces a powerful toxin and causes serious illness, which is sometimes fatal, particularly in young children and the elderly. Symptoms vary from a watery diarrhoea, nausea and abdominal pain to bright red bloody diarrhoea and severe abdominal cramps, usually without fever. Up to 30% of patients develop haematologic uraemic syndrome (HUS). This generally involves young children and E.coli O157 is the major cause of acute renal failures in children in the UK. Fatality rates range from 1% to 5%, but in some outbreaks, for example, involving the elderly, may be much higher. The incubation period is 1 to 8 days, usually 3 to 4 days. The duration of illness is approximately two weeks, unless complications, such as HUS, develop. E-coli O157 disappears from adult faeces within a few days.
Although E.coli O157 can multiply in food, it has a very low infective does involving less than 100 bacteria. Infection results from eating contaminated foods person-to-person spread and direct contact with animals, especially farm animals and their faeces. A failure to wash hands after handling raw meat or going the toilet increases the risk of contamination. The main food vehicles are under cooked meat products, especially burgers and mince, contaminated cooked meat, vegetables fertilised with manure and unwashed, contaminated fruit. Other foods implicated include raw milk, cheese made with unpasteurised milk and apple juice. However, because of low infective does, cross-contamination of many ready-to-eat foods from raw meat is likely to result in illness. The main reservoir of E.coli O157 is the stomach and intestines of cattle and, possibly sheep. The source is faecal material which contaminates carcasses in the slaughterhouse. It survives and multiples in some foods between 3°C and 46°C, although numbers may decline below 3°C. It is destroyed by normal, effective cooking processes. Most outbreak investigations fail to identify a food vehicle.
Following a number of serious outbreaks the food Standards Agency has issued specific guidance for control of E.coli O157, this can be found at: