Verocytotoxin- or Shiga toxin-producing Escherichia coli (VTEC/STEC)

Part of the Communicable Disease Control Manual

Chapter reviewed and updated in May 2019. A description of changes can be found at Updates to the Communicable Disease Control Manual.

Contents


Important note: Shiga toxin-producing E. coli (STEC) may also be referred to as Verocytotoxin-producing E. coli (VTEC) or enterohemorrhagic E. coli (EHEC). STEC is now the preferred term and will be used throughout the rest of this chapter.

Epidemiology in New Zealand

Since the first laboratory confirmed New Zealand case in 1993, the incidence of STEC infection has gradually increased. At least part of this increase is due to changes in laboratory methodology (screening stool samples using culture-independent diagnostic tests), which have been implemented by an increasing number of diagnostic laboratories since mid-2015. This has been associated with an increase in detection of non-0157 serotypes, in particular.

Infection with some STEC serotypes, notably 0157:H7, is associated with a higher frequency of bloody diarrhoea and hospitalisation than other serotypes. The spectrum of presentations associated with STEC infection ranges from no symptoms, to mild, watery diarrhoea, to frank bloody diarrhoea and abdominal cramping. Haemolytic Uraemic Syndrome (HUS) and Thrombotic Thrombocytopenic Purpura are rare complications of STEC, most commonly seen in children and the elderly. Antibiotic treatment for STEC can increase the risk of HUS. Of children with HUS, 12–30 percent will have severe sequelae, including renal and cerebral impairment.

More detailed epidemiological information is available on the Institute of Environmental Science and Research (ESR) surveillance website.

Further information on foodborne illness and STEC is available on the Ministry for Primary Industries website.

Case definition

Clinical description

An acute onset diarrhoeal illness (with or without blood or mucus in stool) [1]

or

Any case with Haemolytic Uraemic Syndrome (HUS) or Thrombotic Thrombocytopenic Purpura (TTP) with or without a history of an acute onset diarrhoeal illness.

Note: In the absence of HUS/TTP, asymptomatic infection or presentations with milder bowel symptoms (eg, occasional loose stools) and/or non-diarrhoeal abdominal symptoms do not meet the case definition.

[1] WHO definition of diarrhoea: ‘the passage of three or more loose or liquid stools per day (or more frequent passage than is normal for the individual).’

Laboratory tests for diagnosis

Laboratory definitive evidence for a confirmed case requires evidence of shiga toxin, which comprises either:

  • culture and isolation of shiga toxin-producing Escherichia coli
  • PCR detection of the genes (stx1 and/or stx2) associated with the production of shiga toxin in E. coli.

All isolates should be referred to the Enteric Reference Laboratory at ESR for further characterisation.

Isolates producing shiga toxin 2 (stx2) are more likely to cause serious human disease than isolates producing shiga toxin 1 (stx1) or both toxins together.

Note: The eae (intimin) and hlyA (enterohaemolysin) genes are accessory virulence factors strongly associated with enterohaemorrhagic E. coli (EHEC). However, finding these genes without the presence of a stx gene does not constitute a positive toxin test.

Case classification

  • Under investigation: A case that has been notified, but information is not yet available to classify it as probable or confirmed.
  • Probable: A clinically compatible illness that is either epidemiologically linked to a confirmed case of the same disease or has had contact with the same common source as a confirmed case – ie, is part of a common-source outbreak.
  • Confirmed: A clinically compatible illness accompanied by laboratory definitive evidence.
  • Not a case: A case that has been investigated and subsequently found not to meet the case definition. (Note: In the absence of HUS/TTP, asymptomatic infection or presentations with milder bowel symptoms (e.g. occasional loose stools) and/or non-diarrhoeal abdominal symptoms do not meet the case definition even if they have positive laboratory results.)

Spread of infection

Reservoir

Commensal of animals. Cattle, sheep, goats, and deer are the primary reservoirs of VTEC/STEC organisms carrying the stx genes. Humans may serve as a reservoir.

Incubation period

2–10 days; median 2–3 days.

Mode of transmission

IIn New Zealand, the majority of notified cases have been associated with animal or farm-environment contact. Raw drinking milk has been confirmed as the source in outbreaks. Overseas, outbreaks have been linked to food contaminated by ruminant faeces in contaminated undercooked hamburger and other meat products; unpasteurised milk; and produce (including melons, lettuce, spinach, coleslaw, apple cider and alfalfa sprouts). Outbreaks have also been linked to faeces-contaminated drinking and swimming pool water, direct contact with animals and person-to-person spread in households, early childhood services, and custodial institutions.

Period of communicability

Faecal shedding persists for up to 1 week in adults and is often longer and quite variable in children [2].

[2] Up to 3 weeks in 30 percent of all children, with a median shedding of 4 to 6 weeks for children under 6 years.

Notification procedure

Attending medical practitioners or laboratories must immediately notify the local medical officer of health of confirmed cases, or if they suspect HUS/TTP.

Separate hospital-based surveillance of paediatric admissions of HUS is provided through the New Zealand Paediatric Surveillance Unit. This surveillance service does not involve medical officers of health.

Management of case

Investigation

In consultation with the attending medical practitioner, obtain a history of ingestion of raw drinking milk or raw milk cheese products, meat products (especially rare ground beef)  and produce (especially leafy greens), exposure to recreational water or untreated water, contact with ruminant animals or their faeces, possible human contacts, and travel. Ensure laboratory confirmation by stool culture or rectal swab has been attempted. Inform the laboratory if STEC is suspected.

Restriction

In a health care facility, only standard precautions are indicated in most cases; if the case is diapered or incontinent, apply contact precautions for the duration of the illness. All cases should remain off work/school until 48 hours after symptoms have ceased. For further details, refer to the exclusion and clearance criteria in Appendix 2: Enteric disease.

Counselling

Advise the case and their caregivers of the nature of the infection and its mode of transmission. Educate about hygiene, especially hand cleaning.

Management of contacts

Identify contacts for investigation, restriction and counselling as appropriate.

Definition

All those with close (eg, household) contact with a case during the period of communicability or who have been exposed to the same contaminated food, water or other source in a common-source outbreak.

Investigation and restriction

All symptomatic contacts should be tested and remain off work/school until 48 hours after symptoms have ceased. No exclusion or testing is required for asymptomatic contacts. For further details, refer to the exclusion and clearance criteria  in Appendix 2: Enteric disease.

Prophylaxis

Nil.

Counselling

Advise all contacts of the incubation period and typical symptoms of STEC infection, and to seek early medical attention if symptoms develop. Educate about hygiene, especially hand cleaning.

Other control measures

Identification of source

Check for other cases in the community. Investigate potential food, water or animal sources of infection only if there is a cluster of cases or an apparent epidemiological link (eg, consumption of raw drinking milk, sprouts or bagged leafy greens).

If indicated, check the water supply for microbiological contamination and compliance with the latest New Zealand drinking-water standards (Ministry of Health 2018).

Disinfection

Clean and disinfect surfaces and articles soiled with stool. For further details, refer to Appendix 1: Disinfection.

Health education

Minimise person to person transmission by educating on the importance of hand-cleaning before handling food.  Hand-cleaning facilities should be available and used after contact with animals. Young children should be supervised during contact with animals and during hand cleaning. Keep farm animals (likely reservoirs) away from food preparation areas. Domestic animals with diarrhoea should be taken to a veterinarian for assessment and treatment.

Implement food safety measures, including checking that water supplies are safe, that produce is not fertilised with animal or human manure, that raw minced meats are cooked properly, that kitchen-handling is hygienic (eg, cooked meats are not returned to the same plate as the raw meat), that fermentation is adequate as per MPI guidelines, and whether or not raw drinking milk is being consumed.

Educate high risk groups about avoiding eating sprouts and consuming raw drinking milk.

If a water supply is involved, liaise with the local territorial authority to inform the public. Advise on the need to boil water.

In early childhood services or other institutional situations, ensure satisfactory facilities and practices regarding hand cleaning; nappy changing; toilet use and toilet training; preparation and handling of food; and cleaning of sleeping areas, toys and other surfaces.

Reporting

Ensure complete case information is entered into EpiSurv.

Where food/food businesses are thought to be involved, inform the Food Compliance group from the Ministry for Primary Industries.

If a cluster of cases occurs, contact the Ministry of Health Communicable Diseases Team and outbreak liaison staff at ESR, and complete the Outbreak Report Form.

References and further information

  • Ministry of Health. 2008. Drinking-water Standards for New Zealand 2005 (Revised 2008). Wellington: Ministry of Health.
  • New Zealand Food Safety. 2019. Manuals and guidelines for food and beverage manufacture. Wellington: Ministry for Primary Industries. URL: https://www.mpi.govt.nz/processing/food-and-beverages/manuals-and-guidelines

  • Collins A, Fallon U, Cosgrove M, Meagher G, & Ni Shuileabhan C. 2017. A 10-year analysis of VTEC microbiological clearance times, in the under-six population of the Midlands, Ireland. Epidemiology and Infection, 145(8), 1577-1583. doi:10.1017/S0950268817000425

  • Dabke G, Le Menach A, Black A, Gamblin J, Palmer M, Boxall N, & Booth L. 2014. Duration of shedding of Verocytotoxin-producing Escherichia coli in children and risk of transmission in childcare facilities in England. Epidemiology and Infection, 142(2), 327-334. doi:10.1017/S095026881300109X

  • Freedman SB, Xie J, Neufeld MS, et al. 2016. Shiga Toxin-Producing Escherichia coli Infection, Antibiotics, and Risk of Developing Hemolytic Uremic Syndrome: A Meta-analysis. Clin Infect Dis. 62(10):1251–1258. doi:10.1093/cid/ciw099

  • Eriksson KJ, Boyd SG, Tasker RC. 2001. Acute neurology and neurophysiology of haemolytic-uraemic syndrome. Arch Dis Child. 84(5):434–435. doi:10.1136/adc.84.5.434


 

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