E.coli

On this page we provide facts from a veterinary perspective on E.coli O157

Overview

Escherichia coli (E.coli) are common bacteria which live in the intestines. Most strains cause no ill effects in healthy humans or animals but some strains are known to cause illness in people, including E.coli O157.

E.coli O157 is common in livestock in the UK and about 5% of cattle may be excreting at any one time. It may be a normal part of ruminant (particularly cattle and sheep) gastro-intestinal flora and causes no clinical signs in infected animals. Other animal species have been identified as excretors but these are the exception rather than the rule.

Useful to know

The organisms are excreted in the faeces and some individual animals may be particularly high shedders posing a greater risk to public health. The bacteria can survive for varying periods of time in the environment eg soil or spread in watercourses.
It is not possible for livestock owners to identify when an animal is infected or excreting. Testing is of limited value as reinfection can easily occur. It is better to assume that in any cattle population there are likely to be varying numbers of excreting animals at any one time and put in place risk reduction measures if there is public access.
No good method has been identified to eliminate or prevent infection in livestock.
The infectious dose (for humans) for O157 is thought to be very low at about 10-100 cells, compared to approximately 100,000 for salmonella. This is only a guide to infectiousness but does mean that hygiene barriers have to be particularly robust.
Human infection is acquired through the oral route from animal faeces, usually from food or water. Inadequate hygiene during the processing of carcases can lead to contamination of meat, which is the most important food vehicle.
About 1000-1200 laboratory-confirmed cases are reported each year in the UK. The majority of patients have diarrhoea or bloody diarrhoea. About 5% of cases develop haemolytic urea syndrome (HUS) and clotting defects. This can cause capillary damage resulting in brain and kidney damage particularly in children and the elderly. O157 is said to be the single biggest cause of kidney failure in children in the UK. Some patients recover after dialysis but some have permanent kidney failure. Antibiotic treatment may exacerbate the symptoms.
Most outbreaks of O157 are associated with food (usually meat) or water. Most cases are not outbreak associated and may have a different epidemiology. Case studies in the UK suggest that animal or animal environment is the single biggest risk factor and there have been some well-documented petting farm incidents, usually affecting small numbers of children.
Children often spread infection to family members or other close contacts.
Prevention of infection between animals and children is hygiene based. Ensure adequate adult supervision particularly of young children to prevent fingers in mouths and make sure hands are washed properly with warm water and soap. Gel wipes may not be adequate to remove all contamination. This is particularly important before eating any food or snacks.
Contact with animals is an important part of children’s development and should not be discouraged, but it is important to recognise the risk that might be present and to take steps to ensure that it can be enjoyed safely.