Verotoxin-producing E. coli (VTEC)

Verotoxin-producing E. coli (VTEC) includes enterohaemorrhagic E. coli (EHEC) and shiga toxin–producing E. coli (STEC).

Notification requirement for verotoxin-producing E. coli

Haemolytic uraemic syndrome is an ‘urgent’ notifiable condition and must be notified by medical practitioners and pathology services immediately by telephone upon initial diagnosis (presumptive or confirmed). Pathology services must follow up with written notification within 5 days.

VTEC/STEC are ‘routine’ notifiable conditions and must be notified by medical practitioners and pathology services in writing within 5 days of diagnosis.

This is a Victorian statutory requirement.

Primary school and children’s services centres exclusion for verotoxin-producing E. coli

Exclude if required by the Secretary and only for the period specified by the Secretary. Contacts are not excluded.

Infectious agent of verotoxin-producing E. coli

Escherichia coli serotypes capable of producing toxins similar to those of Shigella dysenteriae type 1 (shiga toxin/verotoxin) are the causative agents. The most important are E. coli O157:H7, E. coli O111:H8 and E. coli O26:H11.

Identification of verotoxin-producing E. coli

Clinical features

Illness is characterised by severe abdominal pain, and cramping and watery diarrhoea that becomes grossly bloody and lasts for 5–10 days. Fever is usually mild or absent. Asymptomatic infection can occur.

In children aged less than 5 years, infection may lead to haemolytic uraemic syndrome (HUS). This is a disease characterised by microangiopathic haemolytic anaemia, renal failure and thrombocytopaenia, with a high mortality rate. Adults may develop thrombotic thrombocytopaenic purpura (TTP), a similar syndrome, which may be accompanied by neurological abnormalities. HUS and TTP are often complications of infection with serotype O157:H7.

Diagnosis

Diagnosis is confirmed by isolation of the organism from faeces. Other diagnostic methods may be required, including:

• demonstrating the presence of shiga toxin
• serotyping
• use of DNA probes that identify the toxin-producing genes (stx1 and stx2) or the presence of the VTEC virulence plasmid.

Because screening for VTEC is not routine in Victorian laboratories, the test should be specifically requested for people with bloody diarrhoea.

Since a negative stool culture is not exclusionary, HUS/TTP should be considered in the presence of the following:

• acute microangiopathic anaemia on peripheral blood smear
• acute renal impairment (haematuria, proteinuria or elevated creatinine level)
• thrombocytopaenia, particularly during the first 7 days of illness.

Incubation period of verotoxin-producing E. coli

The incubation period is 2–8 days, with an average of 3–4 days.

Public health significance and occurrence of verotoxin-producing E. coli

Recognition of VTEC as an important cause of foodborne illness is relatively recent. The first outbreaks of O157:H7 were reported in the United Kingdom and the United States in the early 1980s. Since then, several large outbreaks have been reported worldwide, and more than 70,000 cases are reported in the United States each year. A particular brand of fermented salami was implicated in a large outbreak in South Australia in 1995. A large 2011 German E. coli outbreak that had a high frequency of HUS was initially thought to be caused by an EHEC strain, but was later confirmed to be an enteroaggregative E. coli producing shiga toxins.

An average of 12 cases of VTEC and 3 cases of HUS are reported in Victoria each year. This is likely to be a significant underestimate of the true burden of disease related to VTEC because of the lack of routine screening of bloody diarrhoea.

Reservoir for verotoxin-producing E. coli

The gastrointestinal tracts of cattle and possibly other domesticated animals act as reservoirs. Humans serve as reservoirs for person-to-person transmission. Prolonged carriage is uncommon.

Mode of transmission of verotoxin-producing E. coli

Ingestion of contaminated food and water, and person-to-person and animal-to-person transmission by the faecal–oral route are responsible for VTEC infection. Undercooked meat, especially ground meat or mince, is a source of infection. Other known food sources have included lettuce, sprouts, salami, unpasteurised milk and fruit juices. The infectious dose necessary to cause disease is thought to be as low as 10 organisms.

Period of communicability of verotoxin-producing E. coli

VTEC is communicable for as long as the organism is present in faeces, which is approximately 1 week in adults and as long as 3 weeks in children.

Susceptibility and resistance to verotoxin-producing E. coli

Everyone is susceptible to infection. Children and the elderly are at higher risk for severe disease. Antibiotic resistance is of increasing concern, and extended spectrum β-lactamase (ESBL)-producing VTEC have now been identified in human isolates.

Control measures for verotoxin-producing E. coli

Preventive measures

Avoid ingestion of inadequately cooked meat and meat products, unpasteurised milk and fruit juices, unwashed salad ingredients, and untreated water. Handwashing after using the toilet, and before and after preparing or eating food is critical.

Control of case

Treatment is generally supportive, particularly maintenance of hydration. The use of antibiotics in the management of VTEC should be avoided as they may increase toxin release and precipitate the onset of HUS. Specialist medical advice should be sought for cases of HUS and TTP. Enteric precautions should be strictly observed in the management of hospitalised cases.

Food handlers, childcare workers and healthcare workers must not work until symptoms have stopped and two consecutive faecal specimens taken at least 24 hours apart are negative for VTEC.

Control of contacts

No exclusion is necessary for contacts, unless the contacts are symptomatic and work in a high-risk occupation, or are children in childcare, kindergarten or primary school. Asymptomatic children in childcare should be screened, and excluded if positive.

Control of environment

Environmental surfaces exposed to infectious material should be thoroughly cleaned. Implicated food should be sampled and destroyed, and contaminated water sources should be treated.

Particular attention to personal and environmental hygiene should be observed in food premises, institutions and childcare centres.

Outbreak measures for verotoxin-producing E. coli

A single case of VTEC or HUS is potentially indicative of an outbreak. Search for other cases and identify people at risk of infection. A source of infection should be sought for all cases of VTEC and HUS. Obtain detailed food and environmental exposure histories from cases, considering food, water or animal sources. Cases in healthcare or childcare facilities should additionally consider the possibility of person-to-person transmission, including from staff. Collect samples of potentially implicated food and send them to the Microbiological Diagnostic Unit at the Doherty Institute for analysis. Antibiotic prophylaxis has not been proven to be either efficacious or safe for the prevention of secondary cases during VTEC outbreaks.

Refer to 'Infection prevention and control - gastroenteritis prevention and outbreak management'for more details on the investigation and management of outbreaks.