Escherichia Coli O157

Synonym: vero cytotoxin-producing Escherichia coli (VTEC) O157, enterohaemorrhagic E.coli.

VTEC O157 is a relatively rare cause of infectious gastroenteritis but may be severe and sometimes fatal, particularly in infants, young children and the elderly. Vero cytotoxin-producing E.coli (VTEC) produce potent toxins and can cause severe disease in man. The most important strain associated with human disease is O157.

• E.coli O157:H7 annual incidence rates of 8/100 000 or greater have been reported. There is an increased incidence in the summer months.¹
• Reservoir: the main reservoir for VTEC O157 is the intestine of healthy cattle although there have been several reports of these organisms in sheep and other animals.² In published studies isolations of VTEC O157 from cattle in the UK have ranged from 0.9% to 15.7%.¹ Carcasses can become contaminated through contact with intestinal contents at slaughter. It can therefore be passed to humans through contaminated food and/or poor hygiene.³
• Person to person spread occurs readily, especially in day-care or chronic care facilities, where frail patients rapidly succumb. The infectious dose of VTEC O157 appears to be very low, probably less than 100 organisms.¹
• In 1997 it was responsible for the death of 20 people in Central Scotland.

Routes of transmission include:

• Contaminated foodstuffs: beef and beef products (e.g. undercooked beef burgers), milk and vegetables have been associated with cases or outbreaks. Outbreaks have been associated also with yogurt, cooked meats, meat pies, cheese, dry cured salami, raw vegetables, unpasteurised apple juice and water. Hamburgers prepared at home and inadequate hand washing by food preparers have been shown to be particular risk factors for sporadic E.coli O157:H7 infections.⁴
• Person to person spread can occur by direct contact (faecal oral - E.coli O157 may be shed in the stool for several weeks), particularly in residential care homes, nurseries and infant schools. Bathing in contaminated water has resulted in small outbreaks.
• Outbreaks and sporadic cases have been linked microbiologically with handling of animals, particularly cattle, and therefore there are risks associated with visitors, especially children, to farm centres.

• Asymptomatic infection is common.
• The incubation period for VTEC O157 infection before the onset of diarrhoea can range from 1 to 14 days with a median of 3 to 4 days.
• Symptoms begin with abdominal cramps and diarrhoea; which turns bloody in 1-2 days in over 70%, the amount of blood being very variable. May also be vomiting and low grade fever. Symptoms are very variable in severity, ranging from a mild diarrhoea to bloody diarrhoea (haemorrhagic colitis) and haemolytic uraemic syndrome.
• Haemorrhagic colitis is characterised by frank bloody diarrhoea, often accompanied by severe abdominal cramps but usually without fever.
• Haemolytic uraemic syndrome is characterised by acute renal failure, haemolytic anaemia and thrombocytopenia. It usually occurs in young children and is the major cause of acute renal failure in children in Britain and several other countries. Haemolytic uraemic syndrome develops in up to 10% of patients infected with VTEC O157.
• Some patients, usually adults, with VTEC O157 infection develop thrombotic thrombocytopenic purpura, in which the clinical features of haemolytic uraemic syndrome are seen together with neurological complications.
• Symptoms usually resolve within two weeks except in cases of haemolytic uraemic syndrome or thrombotic thrombocytopenic purpura. The duration of excretion of the bacteria is usually up to a week but has been observed for much longer periods particularly in children.

• Other causes of gastroenteritis
• Intussusception
• Ischaemic colitis
• Appendicitis
• Ulcerative colitis
• Crohn's disease
• Other causes of gastrointestinal bleeding

• Diagnosis is made on stool sample (needs to be collected promptly). Not all labs routinely screen for E.coli O157 - contact local laboratory if in doubt.
• Other investigations include full blood count, renal function and electrolytes (risk of haemolytic uraemic syndrome and thrombotic thrombocytopenic purpura).

• Public health physicians should be notified immediately. Exclusion of infected individuals from day-care facilities until two negative stool cultures would seem reasonable. Patients need counselling on hazards of eating undercooked food, unpasteurised milk products and juices.
• There is no specific treatment for these infections in humans and each phase of the disease is treated symptomatically.
• Management is supportive: watch for signs suggestive of haemolytic uraemic syndrome (pallor, weight gain, oligouria). Consider regular monitoring of urinalysis, renal function and electrolytes, and full blood count (haematocrit and blood film for fragmented red blood cells - which strongly suggests progression to haemolytic uraemic syndrome and hospital admission is required).
• Avoid antimotility agents as these may promote haemolytic uraemic syndrome.
• Antimicrobial treatment may not be beneficial. Antibiotic treatment may increase the risk of haemolytic uraemic syndrome in children⁵ so antibiotics are not advised unless stool culture indicates that the pathogen is one that is appropriately treated with antibiotics.²
• Development of haemolytic uraemic syndrome and thrombotic thrombocytopenic purpura requires appropriate clinical management.
• Possible for treatment in the future: toxin binding resins and neutralising antibodies. No vaccine is available.

• VTEC gives rise to a haemorrhagic colitis.
• 3-7% of cases proceed to haemolytic uraemic syndrome (20% in some outbreaks). The case fatality rate of haemolytic uraemic syndrome is about 10%.
• Thrombotic thrombocytopenic purpura also occurs.

• The fatality rate of VTEC O157 infections is very variable and depends on the ages of the groups affected.
• Fatality rates ranging from 1 to 5% have been reported but may be much higher in some institutional outbreaks.¹

• Minimise the contamination of carcasses at slaughter.
• Prevent cross contamination from raw to cooked food.
• Avoid undercooking beefburgers.
• Rigid hygiene rules for food handlers.