E.coli

Epidemiology of Infectious Diseases: E.coli

Causal agent
Six major categories of Escherichia coli strains cause diarrhoea1.

enterohaemorrhagic
enterotoxigenic
enteroinvasive
enteropathogenic
enteroaggregative
diffuse-adherent

E. coli serotype O157:H7. -Gram-negative rod-shaped bacterium producing Shiga toxin(s)

The most serious illness in humans is caused by verocytotoxic E. coli (VTEC) (also known as enterohaemorrhagic E. coli), The most common VTEC strain in Europe and North America is

E. coli O157:H7. However, other serotypes have frequently been involved in sporadic cases and outbreaks2.

Common clinical features

  • VTEC O157 can cause a range of symptoms from asymptomatic carriage to mild diarrhoea or bloody diarrhoea (haemorrhagic colitis) and haemolytic uraemic syndrome (HUS).
  • HUS is characterised by acute renal failure, haemolytic anaemia and thrombocytopaenia (lowered platelets). It usually occurs in young children and is the major cause of acute renal failure in children in Britain and several other countries. HUS develops in up to 10% of patients infected with VTEC O157 (HPA)1.
  • Children <5 years old and the elderly are more likely to develop serious complications.
  • Fatality rates ranging from 1 to 5% have been reported in the UK (HPA).

Epidemiology

  • Important cause of bloody diarrhoea in Europe.
  • In 2005 there were 946 laboratory confirmed cases of VTEC 0157 in England and Wales (HPA).
  • The highest incidence rates in the UK are seen in children < 5 years.
  • The highest rates have been observed in rural areas particularly in Scotland2.

Reservoir
The gastointestinal tract of animals - cattle are the most important reservoir.

Mode of transmission

  • Primarily through the consumption of contaminated, undercooked or raw foods, (particularly ground beef) and unpasteurised milk. 
  • Other foods implicated in outbreaks of E.coli O157:H7 include undercooked hamburgers, dried cured salami, lettuce, yogurt, cheese and milk and radish sprouts.
  • Cross contamination during food preparation.
  • Person to person via the faeco-oral route is common.
  • Direct contact with animals, e.g. school visits to farms.  
  • Waterborne transmission occurs through swimming in or consuming contaminated water.
  • The infectious dose of VTEC O157 appears to be very low, probably less than 100 organisms2.

Incubation period
2-10 days, median 3-4 days.

Period of Communicability
While excreting pathogen, up to a week in adults and up to three weeks in children.
An asymptomatic carrier state has been reported.

Prevention and control 

  • Developing farm and slaughterhouse-based methods to decrease contamination of meat; encouraging use of irradiation to increase the safety of ground beef; identifying ways to prevent contamination of foods eaten raw (e.g., produce).
  • Follow correct food hygiene practices for food preparation and cooking in domestic and commercial kitchens as described by the WHO Five keys to safer food3.

These include;

  • Prevent cross contamination of raw and cooked food by washing hands before, during and after food preparation.  Wash and sanitize all equipment, surfaces and utensils used for food preparation.
  • Separate raw and cooked food, and use separate equipment and utensils for handling raw food.
  • Cook food thoroughly (until centre of food reaches at least 70oC), especially poultry, meat, eggs and seafood. 
  • Reheat cooked food thoroughly, and store cooked and raw food at a safe temperature.
  • Use safe water and raw materials, e.g. pasteurized milk and water.
  • Wash fruit and vegetables.

References

  1. Heymann D L, editor, Control of Communicable Disease Manual. 18th ed. American Public Health Association; 2004.
     
  2. Hawker J, Begg N, Blair I, Reintjes R, Weinberg J. Communicable Disease Control Handbook, Blackwell, 2005.
     
  3. World Health Organization: 5 Keys to Safer Food. Available at http://www.who.int/foodsafety/publications/consumer/5keys/en/

Further Resources

Guidelines for the control of infections with VTEC and particularly E.coli 0157 have been published by the PHLS, available at
Communicable Disease and Public Health, 2000; 3 (1) 14-23

Guidelines for preventing the transmission of gastrointestinal illess caused by infections (including VTEC), available at
Communicable Disease Report (CDR) Review 1995; 5: R157-R172

© CM Kirwan 2006