Shiga toxinproducing E. coli (STEC)

Enterohaemorrhagic E. coli cause a haemorrhagic colitis, haemolytic uraemic syndrome and thrombotic thrombocytopaenic purpura by the production of verotoxins.

Enterohaemorrhagic serotypes include O157.H7.

• Enterohemorrhagic Escherichia coli) (STEC, EHEC)
  • the enterohaemorrhagic E. coli (EHEC) are now generally referred to as Shiga toxinproducing E. coli (STEC). They are capable of producing the toxins Shiga toxin 1 (stx1) and Shiga toxin 2 (stx2) (named due to their similarity to the toxin produced by Shigella dysenteriae type 1)
    • Shiga toxin is named for the Japanese microbiologist Kiyoshi Shiga (1870-1957), for whom the genus Shigella is named, inasmuch as the toxin produced by Shigella dysenteriae type 1 is very similar to the Stx1 and Stx2 produced by STEC (2)
      • can be further divided into several subtypes based on variations in amino acid sequences. Stx1 includes three subtypes (Stx1a, Stx1c, and Stx1d), while Stx2 contains at least seven subtypes (Stx2a to Stx2g) (3)
    • Stx2 production is more often associated with severe diseases than strains producing Stx1 (2)
  • STEC replaces the previous terminology ‘verocytotoxin-producing E. coli (VTEC)’.
  • Shiga toxin can be produced by both O157 and non-O157 serotypes. All O157 types (stx +ve and –ve) and non-O157 STEC (i.e. stx +ve) infections require urgent Public Health action
  • STEC comprise one of four generally recognized groups of E coli causing diarrhoea in humans who acquire infections by ingestion of contaminated food or water or another fecal-oral route (2)
    • other groups of E coli causing diarrhoea are EIEC, enteroinvasive E coli; EPEC, enteropathogenic E coli; ETEC, enterotoxigenic E coli
  • STEC is a foodborne zoonotic pathogen that causes diarrhea, hemorrhagic colitis (HC), and hemolytic uremic syndrome (HUS) worldwide (3)
  • natural reservoir for STEC is ruminant animals, notably cattle, in which STEC can occur as normal intestinal flora
  • STEC human infection can occur through the ingestion of contaminated foods, person-to-person transmission, or contact with animal reservoirs (3)
    • STEC infectious dose is much lower than that of many other enteropathogens
      • have an estimated 10~100 organisms capable of causing infection, which increases the risk of infection from exposure and facilitates person-to-person transmission
  • clinical presentation of STEC infection is diarrhoea, with or without blood present, which may be intermittent, watery, or nonwatery, often accompanied with abdominal cramping, nausea, headache, vomiting, and fever (2)

They colonise the large intestine where they cause diffuse mucosal haemorrhages.

Approximately, 10-15% of people infected with STEC go onto develop HUS.

Children under 15 years old and older adults over the age of 65 years4 are more likely than other age groups to develop STEC-related HUS, particularly children under 5 years. In
England between 2009 and 2012, three quarters of HUS cases occurred in children (0-14 years)

Treatment is mainly supportive.

Summary:

Reservoir:

• Gastrointestinal tract of ruminants (in the UK mainly cattle, sheep and goats). Other animals and birds acts as transmission vectors

Transmission:

• Faecal-oral route
  • ingestion of contaminated food (particularly undercooked meat, minced beef, salad products including water cress) water or unpasteurized milk
  • person-to-person spread
  • direct/indirect contact with an infected animal or their faeces
  • environmental exposure e.g. swimming/playing in contaminated water, streams or ponds
• Seasonal outbreaks have been associated with farm visits to feed and handle calves and lambs

Incubation period:

• Usually 2-4 days for STEC O157 and similar for most strains of non-O157 STEC

Infectivity:

• shedding of organisms depending on strain of STEC and age of patient may be prolonged. It tends to be shorter in adults but there have been reports of children shedding for over 6 weeks

Reference:

1. PHE (2019). Recommendations for the Public Health Management of Gastrointestinal Infections
2. Hunt JM. Shiga toxin-producing Escherichia coli (STEC). Clin Lab Med. 2010 Mar;30(1):21-45.
3. Sui X et al. Characteristics of Shiga Toxin-Producing Escherichia coli Circulating in Asymptomatic Food Handlers. Toxins (Basel). 2023 Nov 2;15(11):640.