Escherichia coli O157

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

See also the separate articles on Gastroenteritis in Children and Gastroenteritis in Adults and Older Children.

What is Escherichia coli O157?

Shiga toxin-producing Escherichia coli (STEC), also known as Vero cytotoxin-producing Escherichia coli (VTEC), are a group of bacteria that cause infectious gastroenteritis. The most frequently reported STEC strain to cause illness in England and Wales is E. coli O157.³

Escherichia coli O157 is very important because it may be severe and sometimes fatal, particularly in infants, young children and the elderly.

Important complications are haemolytic uraemic syndrome (HUS) and thrombotic thrombocytopaenic purpura (TTP).

E. coli strains are common in the human intestine. Most are harmless, but the vero cytotoxin-producing E. coli (VTEC) produce potent toxins (vero cytotoxins) and may cause severe disease.

How common is Escherichia coli O157? (Epidemiology)³

• A total of 539 confirmed cases of Echerichia coli O157 were reported in England and Wales in 2019.

• Children aged 1 to 4 years had the highest incidence of infection (3.28 per 100,000 population).

• Nearly one-third of confirmed STEC O157 cases in England were hospitalised and 3% were reported to have developed haemolytic uraemic syndrome (HUS).

• Five outbreaks of STEC involving 65 cases in England were investigated in 2019.

• The duration of excretion of the bacteria is usually ≤1 week. The greatest transmission is probably in the acute diarrhoeal phase. However, shedding of E. coli can occur from asymptomatic patients, and also can continue for several weeks after recovery from the illness.⁴

Risk factors³

The main reservoir is cattle and other ruminants. Transmission to humans occurs through:

• Consumption of contaminated food or water.

• Exposure to a contaminated environment involving direct or indirect contact with animals or their faeces.

The low infectious dose of STEC means that once in the population, person-to-person spread is common.

Infection can occur via the following routes:

• Contaminated foods:⁵
  

  • The main reservoir for E. coli O157 is the intestine of healthy cattle and other farm animals.⁶ The bacteria can survive in faeces and soil. Carcasses can become contaminated through contact with intestinal contents at slaughter.

  • Mainly, inadequately cooked minced beef (often in the form of beefburgers) and milk, yoghurt and cheese (unpasteurised and contaminated post-pasteurisation).⁷ Also, sausages, venison and cold sliced meats - eg, salami.

  • The UK differs from other countries in that it has had a considerable number of outbreaks associated with butchers, but very few caused by contaminated burgers.⁸

  • Outbreaks have also occurred through yoghurt, cooked meats, meat pies, cheese, dry-cured salami, contaminated vegetables (eg, sprouts, leaf lettuce or spinach), unpasteurised apple juice or cider.

• Contact with farm animals - direct spread can occur from animals to their keepers, to farmers' households, and to farm visitors.

• Person-to-person spread, particularly in households, nurseries, and infant schools.

• Via infected water - eg, faecal-contaminated lakes or streams, non-chlorinated domestic water supply, swimming pools and home paddling pools.

Clinical features and complications³

Infection is associated with a broad spectrum of illness ranging from mild diarrhoea and haemorrhagic colitis to the potentially fatal haemolytic uraemic syndrome.⁹ Infection may also cause thrombotic thrombocytopaenic purpura (TTP).

There should be a high index of suspicion of VTEC infection in a child who has recently (within 21 days) visited an open farm, where there has been contact with another known or suspected case of VTEC, or who is living in an area where a suspected or confirmed outbreak of VTEC infection exists.

VTEC infection should always be suspected where acute bloody diarrhoea is present, and will often be accompanied by abdominal pain, fever, pallor, petechiae and oliguria, which are markers of more severe disease. E. coli O157 can cause a range of symptoms - from asymptomatic infection or mild diarrhoea, to bloody diarrhoea (haemorrhagic colitis) and HUS. Possible clinical scenarios are:

• No symptoms or mild diarrhoea.

• Painful diarrhoea or haemorrhagic colitis:⁴
  

  • Typically, this starts as diarrhoea and abdominal cramps. In most cases, the diarrhoea becomes bloody after 1-3 days.

  • Patients usually have no fever by the time they see a doctor.

  • Note: compared to other forms of bacterial gastroenteritis, the abdominal pain is generally more severe; abdominal tenderness on examination is common and defecation tends to be painful.

• Haemolytic uraemic syndrome (HUS):
  

  • A triad of acute kidney injury (oliguria and oedema), haemolytic anaemia and thrombocytopenia.

  • It mainly occurs in young children and is the major cause of acute kidney injury in children in Britain.

  • HUS, if it occurs, is usually diagnosed 5-13 days after the onset of diarrhoea, and thrombocytopenia is usually the first feature.⁴

  • HUS develops in up to 15% of patients infected with E. coli O157.

• Thrombotic thrombocytopenic purpura (TTP):
  

  • Some patients, usually adults, develop TTP.

  • This is similar to HUS, but with less renal involvement and more prominent neurological features.

Differential diagnosis

• Other causes of gastroenteritis.

• Intussusception.

• Inflammatory bowel disease - ulcerative colitis or Crohn's disease.

• Ischaemic colitis.

• Appendicitis.

• Other causes of gastrointestinal bleeding.

• Other causes of HUS.

Investigations³

• Diagnosis is usually made from a stool sample. Definitive diagnosis depends on microbiological isolation and characterisation of the causative organism or the demonstration of antibodies to O157 lipopolysaccharide.

• UK NHS and public health laboratories routinely test faecal specimens from all cases of acute diarrhoeal illnesses for the presence of VTEC but any request should clearly contain the information that the patient has bloody diarrhoea and that VTEC is a possible diagnosis.

• Initial microbiological identification of a suspected VTEC takes 24-48 hours and reference laboratory confirmation takes a further 48-72 hours. Therefore, the appropriate clinical and public health management of potential VTEC disease should not be delayed whilst awaiting confirmatory microbiological results.

• Where the initial laboratory investigations have not isolated a potential VTEC but there is strong clinical suspicion of VTEC infection, further investigations must be performed by the appropriate reference laboratory to detect atypical or unusual VTEC strains - eg PCR detection of vero cytotoxin genes and other virulence markers. Serum for specific antibodies may also be sent at least 10 days after the onset.

• Blood tests: FBC (If VTEC is confirmed, a high white cell count is a marker of severity and is associated with increased likelihood of HUS, renal function and electrolytes. Falling platelet count or fragmented erythrocytes suggest HUS.⁴

When to see a doctor

See also the separate Haemolytic Uraemic Syndrome and Thrombotic Thrombocytopaenic Purpura articles.

Always seek urgent specialist advice whenever a child is reported to have had a single acute episode of bloody diarrhoea. Referral is an emergency where significant dehydration, acute abdominal pain, or other clinical features indicate the possible need for surgical intervention.

Any child suspected of suffering with E. coli 0157 should be assessed urgently by a paediatric specialist. Consider hospital admission if clinical features suggest E. coli O157 (eg, acute bloody diarrhoea, especially without fever or with very painful diarrhoea).⁴

Infectious bloody diarrhoea must be reported promptly, preferably by telephone. Management is supportive:

Escherichia coli O157 treatment and management¹⁰

• Early fluid resuscitation: intravenous volume expansion has been associated with renal protection in VTEC infections.

• Monitor for features of HUS (oliguria, oedema and weight gain, pallor; monitor blood count, platelets, renal function and electrolytes).

• Avoid antidiarrhoeal drugs and opioid analgesics. An association with the risk of developing HUS or neurological complications of VTEC infection has been reported with the use of antimotility agents and opioid analgesics.

• There is some evidence that antibiotic treatment may be a risk factor for HUS and there is insufficient evidence to recommend antibiotic treatment for VTEC infection. Some reports have suggested that antibiotics are contra-indicated.¹¹

• Non-steroidal anti-inflammatory drugs should be avoided, as they may have adverse effects on renal blood flow.

• Public health measures are important to limit outbreaks - both to identify and remove primary sources of infection but also to prevent secondary infections.

Infection control measures

• Secondary infection can occur in household settings. Any cases of diarrhoea, arising in close contacts of a diagnosed or suspected case of VTEC infection, must be investigated promptly.

• Advice should be given that good personal hygiene must be maintained by all children and adults in any household where one or more cases of VTEC infection are diagnosed or suspected.

• The use of prophylactic antibiotics is therefore not recommended.

• Any child aged 5 years or younger who has been diagnosed with a VTEC infection should not go to a school, preschool group, nursery or other childcare or child-minding group until well, and tests have shown them to no longer be infectious (two negative faecal specimens taken not less than 24 hours apart, the first to be taken not earlier than 24 hours after symptoms have ceased).

• Older children should not go to school and other social settings until they are well and 48 hours have elapsed after passing their first normal stool. In children older than 5 years who are not able to maintain good personal hygiene, the local Public Health Service should be consulted on the need to undertake microbiological testing to ensure that they are free from infection before returning to school.

Prognosis^{3 4}

• Most patients recover spontaneously by 1-2 weeks after symptoms start. Infants, children and the elderly are at greatest risk of complications.

• Risk of HUS:
  

  • For children aged <10 years, the risk of developing HUS is about 15%.

  • Overall, approximately 5% of infected patients develop HUS.

  • The case fatality rate of HUS is about 10%.

• Risk of death:
  

  • The fatality rate of E. coli O157 infections is very variable and depends on the ages of the groups affected.

  • Fatality rates ranging from 1-5% have been reported, but may be much higher in some institutional outbreaks.

Escherichia coli O157 prevention

This mainly involves adequate hygiene to prevent contamination of food and person-to-person spread. It particularly applies to farms, abattoirs and those working in healthcare, nurseries and food provision.

Correct food preparation is also important:

• Washing of raw vegetables.

• Adequate cooking of meat, especially beefburgers.

• Pasteurisation of dairy products.

Advice to the public from Public Health England is:³

• Safe food preparation:
  

  • Fully cook minced meat products like beefburgers or meat loaf so that they are coloured all the way through, and no blood runs from them.

  • Keep cooked and uncooked meats separately; store uncooked meat on the bottom shelf of the fridge to avoid dripping raw meat juices on to other food.

  • Never put cooked food back on a plate which has had fresh uncooked meat on it.

  • Thoroughly wash all salads and vegetables that are to be eaten raw.

  • Avoid eating and drinking unpasteurised milk and dairy products.

  • Boil any drinking water if you are unsure of its source.

• Do not swim in water that may be contaminated.

• Hygiene:
  

  • Thoroughly wash hands after using the toilet, handling raw meat, before meals and after contact with animals.

  • Ensure children wash their hands with warm water and soap after contact with animals, particularly while on farm visits.

  • If someone has E. coli infection, wash all dirty clothes, bedding and towels in the washing machine on the hottest cycle possible. Clean toilet seats, toilet bowls, flush handles, taps and wash hand basins after use, with detergent and hot water, followed by a household disinfectant.

  • If you have E. coli infection you should not prepare food for others.

'Probiotics':

• Some sources suggest that 'probiotics' (eg, certain strains of lactobacilli) may help to prevent gastrointestinal infections, because they colonise the gastrointestinal tract and theoretically prevent pathogenic organisms from infecting the gut.¹²