The facts about... Verocytotoxin-producing Escherichia coli (VTEC)
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What are Verocytotoxin producing Escherichia coli (VTEC)?Verocytotoxin producing Escherichia coli [VTEC] are bacteria responsible for a range of illnesses in humans from mild diarrhoea to severe colitis. They are so called because of a distinguishing laboratory test using Vero cells. There are a number of different VTEC bacteria, the commonest one responsible for human disease in the United Kingdom being E. coli 0157. Laboratory isolations of E. coli 0157 in the United Kingdom have risen steadily from less than 10 each year in the early 1980s to 656 in 1994 and 1,039 in 1995. At present most of these infections are diagnosed in children under 5 years of age and the majority of cases occur in the summer and early autumn. However, the true incidence of this infection is probably much higher as many patients with diarrhoea do not have laboratory investigations and at present not every Microbiology laboratory will look for this bacterium routinely in all faeces samples. What symptoms do VTEC cause?Diarrhoea is the commonest symptom produced by E. coli 0157 and the other VTEC infections. The incubation period for the illness is usually one to six days with an average of about two days. It is usually a self-limiting, mild diarrhoea which settles within two weeks but it can progress to a more serious colitis with severe abdominal pain and bloody diarrhoea. Nearly half of all infected patients have blood in their faeces. About 5% of cases go on to develop the haemolytic uraemic syndrome, which is a type of acute renal failure associated with anaemia. This syndrome, which has a fatality rate of about 10%, is a more likely complication of VTEC infections in children and, to a lesser extent, the elderly. Another rare complication is thrombotic thrombocytopenia purpura, during which the patient develops a fever and an extremely low platelet count associated with the formation of blood clots which can limit the blood supply to the brain giving rise to neurological complications. This complication usually affects adults rather than children, and the prognosis is poor. How are VTEC infections diagnosed?The diagnosis is usually confirmed by growing the bacterium from faecal samples on special culture media in Microbiology laboratories. Occasionally a pair of blood samples can be examined to detect rising levels of antibodies produced by the patient in response to the infection. Gene probes are used in research laboratories to detect the verocytotoxin in either faeces or in bacteria isolated from faeces. How are VTEC cases treated?As these infections are usually self-limiting, only simple measures such as plenty of fluids, a light diet and rest are needed. Whether antibiotic treatment is beneficial in this infection has yet to be established. If the haemolytic uraemic syndrome, thrombotic thrombocytopenia purpura or renal failure should develop, then these are treated by conventional means. Where do VTEC infections come from and how do they spread to humans?Cattle are thought to be the main reservoir of infection. Several large outbreaks in the USA have been associated with undercooked beefburgers. Other suggested sources of infection include contaminated pasteurised and unpasteurised milk, yoghurt and faecally contaminated raw vegetables and water. Only small numbers of bacteria, i.e. less than 100 organisms, are necessary to cause illness. Outbreaks due to the spread of the infection from person to person have occurred within households, nurseries and infant schools. In addition, direct contact with infected animals, particularly on farms or in animal sanctuaries, have also been reported as a source of infection. What measures can be taken to control the spread of VTEC?As the recognition of VTEC infections is fairly recent, the best ways of controlling these diseases are still being determined and may be modified in the light of future experiences. All cases should be reported to a Consultant for Communicable Disease Control, or their equivalent, and notified if the infection is thought to be as a consequence of food poisoning. Cases admitted to a hospital should be nursed in a single room with enteric precautions during the acute diarrhoeal phase of the illness. Environmental Health Officers and Public Health doctors must satisfy themselves as to the adequacy of hygiene, and arrangements for handwashing and toilet facilities within the home of any reported case or contact. Handwashing by children must be supervised in nurseries and infant schools. Cases who pose a special risk of spreading the infection include:
All these cases should be excluded from their work or school until two faecal samples taken at intervals of not less than 48 hours have been found to be clear of the organism. Cases who pose no special risk can return to work or school 48 hours after their diarrhoea has settled. Contacts of cases who are themselves within the groups posing a special risk of spreading the infection should have faeces samples tested to see if they are also infected by VTEC bacteria. Contacts who are children under five years of age attending play groups, pre-school nurseries or other similar groups as well as older children and adults who are unable to implement good standards of personal hygiene should, in addition, be excluded from their work or school until their faeces samples have been found to be clear of the organism. The Department of Health's Chief Medical Officer advises that exposure to VTEC bacteria as well as other food poisoning organisms can be significantly reduced by cooking beefburgers thoroughly until the juices run clear and there are no pink areas inside. Vulnerable groups such as children, the elderly and immunocompromised patients should also avoid consumption of raw milk.
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