Escherichia Coli O157

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

Incidence rates of 1-3:100,000 are reported. Rates are highest during July-October. The main reservoir for E. coli O157 is the intestine of healthy cattle. The bacteria can survive in faeces and soil. Carcasses can become contaminated through contact with intestinal contents at slaughter. The infectious dose of E. coli O157 appears to be very low, probably fewer than 100 organisms.

Infection can occur via the following routes:

• Contaminated foods:
  • Mainly, inadequately cooked minced beef (often in the form of beefburgers) and milk (unpasteurised and contaminated post pasteurisation).
  • Outbreaks have also occurred through yoghurt, cooked meats, meat pies, cheese, dry cured salami, raw vegetables, unpasteurised apple juice and water.
• Contact with farm animals - direct spread can occur from animals to their keepers, to farmers’ households, and to farm visitors.
• Person to person spread, e.g. in families or institutions.
• Via infected water, e.g. there have been outbreaks from infected swimming or paddling pools.

Transmission:

• The incubation period is 1-14 days, usually 3-4 days.
• The duration of excretion of the bacteria is usually ≤1 week. The greatest transmission is probably in the acute diarrhoea phase. However, shedding of E. coli can occur from asymptomatic patients, and also can continue for several weeks after recovery from the illness.^3,4

E. coli O157 can cause a range of symptoms - from asymptomatic infection or mild diarrhoea, to bloody diarrhoea (haemorrhagic colitis) and HUS.

Consider possible E. coli O157 in patients with acute bloody diarrhoea, especially those without fever on examination, and those with very painful diarrhoea.⁴

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 renal failure (oliguria and oedema), haemolytic anaemia and thrombocytopenia.
  • It mainly occurs in young children and is the major cause of acute renal failure in children in Britain.
  • HUS, if it occurs, is usually diagnosed 5-13 days after the onset of diarrhoea, and thrombocytopaenia 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.³

In uncomplicated cases, symptoms usually resolve within two weeks.

• 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

• Diagnosis is usually made on stool sample
  • The sample needs to be collected promptly. Identification from stool samples may not be successful if specimens are obtained > four days from the onset of symptoms.⁵
  • PHLS laboratories are instructed to look for E. coli O157 from all cases of diarrhoea. However, some laboratories may not routinely screen for this infection - contact local laboratory if in doubt.
• E. coli O157 can also be identified using serum antibodies (useful when stool culture negative) and saliva samples.
• Blood tests - full blood count, renal function and electrolytes:
  • Falling platelet count⁴ or fragmented erythrocytes³ suggest HUS.

See also the separate article Haemolytic Uraemic Syndrome.

Overview

1. Notify public health physician of suspected or proven cases.
2. Consider hospital admission if clinical features suggest E. coli O157 (e.g. acute bloody diarrhoea, especially without fever or with very painful diarrhoea):⁴
   • Admission may be helpful for fluid replacement, nephroprotection (see below) monitoring or isolation purposes.
   • Admit patients who are unwell or if suspected complication, e.g. HUS.
3. Treatment is supportive, e.g:
   • Correct fluid and electrolyte imbalance.
   • Monitor for features of HUS (oliguria, oedema and weight gain, pallor; monitor blood count, platelets, renal function and electrolytes).
   • Avoid drugs which may increase the risk of HUS - antibiotics, anti-motility agents, narcotics and NSAIDs.⁴

Details of supportive treatment

Authors of a Lancet review⁴ and others⁶ suggest that optimum intravenous rehydration is important to provide nephroprotection. They suggest that standard rehydration protocols may be inadequate in this scenario, because vascular leakage is not compensated. The Lancet authors advise the following protocol:

• They have thrombocytopenia, with or without anaemia, but the serum creatinine concentration remains normal.
• Rarely, a red cell transfusion may be needed for patients with symptomatic anaemia but no renal insufficiency.

Infection control measures

The PHLS has published detailed guidance for preventing transmission once a case is identified.⁵ In summary:

• Children with VTEC infection - should be excluded from nurseries etc. until two consecutive negative faecal specimens, taken after recovery and at least 48h apart, have been obtained.
• Children in the household of an infected person - microbiological clearance of children under 5 years who are household contacts of cases is recommended to reduce the risk of outbreaks in childcare nurseries (i.e. need two consecutive negative faecal specimens at least 48h apart).
• Outbreaks in a children's daycare facility - if an outbreak is confirmed or is very likely, the facility should be closed temporarily and undergo thorough environmental cleansing.
• Infection control measures should take into account people who pose a greater risk of transmitting infection, e.g:
  • Food handlers.
  • Healthcare and nursery staff.
  • Children under 5.
  • Older children/adults who are unable to implement good hygiene.
  These groups should normally stay off work/school/nursery until they have 2 negative stool tests, 48 hours apart.

• Most patients recover spontaneously by 1-2 weeks after symptoms start.^3,7 Infants, children and the elderly are at greatest risk of complications.
• Risk of HUS:
  • For children <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% to 5% have been reported, but may be much higher in some institutional outbreaks.⁸

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 the HPA is:⁷

• 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' (e.g. certain strains of lactobacilli) may help prevent gastro-intestinal infections, because they colonize the gastrointestinal tract and theoretically prevent pathogenic organisms from infecting the gut.⁹