Escherichia coli O157 (STEC)

Background

Shiga toxin-producing Escherichia coli (STEC), previously referred to as Verotoxigenic E. coli (VTEC), are a group of bacteria which can cause gastrointestinal illness in humans.

STEC are widespread in the environment and can colonise the gastrointestinal tract of farmed, wild, and domesticated animals and birds and can be shed in their faeces. Cattle, sheep and goats are considered to be the main reservoir of infection, although STEC causes no clinical signs of infection in the animal.

In Scotland, the most common strain of STEC to cause illness is E. coli O157. The reported rates of E. coli O157 in Scotland rose substantially in the mid-1990s and remain consistently high compared to other countries within the UK and Europe. Infection is also caused by a range of other serogroups. More information on this can be found in our annual surveillance report.

Modes of transmission

Transmission to humans can occur as a result of direct contact with STEC-contaminated faecal material. This can happen by:

  • swallowing bacteria which are on hands after contact with animals or places and items where their faeces is, or may have been - hands do not need to look dirty to have bacteria on them
  • drinking untreated water from lochs, rivers and streams, or from private water supplies that have not been adequately treated
  • eating contaminated food such as undercooked meat, unpasteurised milk including dairy products made from unpasteurised milk or raw vegetables and salad
  • eating other food items that have become cross-contaminated by poor hand hygiene after handling raw meat or other contaminated foods, or by an infected person who has handled food
  • spread from another person infected with STEC - an infected person can pass the infection on to others fairly easily when hand hygiene is poor, through:
    • direct contact from person to person with inadequately washed hands
    • the environment, such as the bathroom, if this becomes contaminated with their faeces for example, through touching toilet flushes, taps, and is not cleaned regularly and adequately

The time between swallowing the bacteria and symptoms starting, also known as the incubation time, is mostly between one and 14 days but commonly around three to four days. Not everyone who is infected with STEC will have symptoms.

Symptoms

Symptoms of STEC infection range from:

  • asymptomatic infection
  • mild non-bloody diarrhoea
  • bloody diarrhoea
  • abdominal pain
  • occasionally a fever

Serious outcomes of infection can include haemolytic uraemic syndrome (HUS) which has been shown to be a major cause of acute renal failure in children in Scotland.

Information about the symptoms of STEC infection is available on the NHS Inform website.

Guidance

For all infection prevention and control guidance visit the A-Z ​pathogens section of the National Infection and Prevention Control Manual.