Page content: Victorian statutory requirement | Infectious agent | Identification | Incubation period | Public health significance & occurrence | Reservoir | Mode of transmission | Period of communicability | Susceptibility & resistance | Control measures | Outbreak measures | Additional sources of information

Victorian statutory requirement

Haemolytic uraemic syndrome (Group A disease) must be notified immediately by telephone followed by written notification within five days.

VTEC and STEC (Group B disease) must be notified in writing within five days of diagnosis.
School exclusion: exclude if required by the Secretary and only for the period specified by the Secretary. Contacts are not excluded.

Infectious agent

Escherichia coli serotypes capable of producing toxins (Shiga-like or Vero-toxins) similar to those of Shigella dysenteriae type 1 are the causative agents. The most important are E. coli O157:H7, E. coli O111:H8 and E. coli O26:H11.

Identification

Clinical features
Illness is characterised by severe abdominal pain and cramping and watery diarrhoea which becomes grossly bloody and lasts five to ten days. Fever is usually mild or absent. Asymptomatic infection can occur.

In children aged less than five years and the elderly, infection may lead to haemolytic uraemic syndrome (HUS). This is a disease characterised by renal failure, a high mortality rate and thrombotic thrombocytopaenic purpura (TTP). HUS and TTP are complications of infection with serotype O157:H7.

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

• demonstrating the presence of Shiga-like toxins
• serotyping
• DNA probes that identify the toxin producing genes or the presence of the VTEC virulence plasmid.

As screening for VTEC is not routine in Victorian laboratories the test should be specifically requested for persons with bloody diarrhoea.

As a negative stool culture is not exclusionary, HUS 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 seven days of illness.

Incubation period

The incubation period is two to eight days, with an average of three to four days.

Public health significance & occurrence

Recognition of VTEC as an important cause of food-borne illness is relatively recent. The first outbreaks of O157:H7 were reported in the United Kingdom and United States in the early 1980s.

Since then several large outbreaks have been reported worldwide and over 70,000 cases are reported in the US each year. A particular brand of fermented salami was implicated in a large outbreak in South Australia in 1995.

An average of five cases of VTEC and three 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 due to the lack of routine screening of bloody diarrhoea.

Reservoir

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

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 ten organisms.

Period of communicability

VTEC is communicable for as long as the organism is present in faeces which is approximately one week for adults but may be as long as three weeks in children.

Susceptibility & resistance

Everyone is susceptible to infection. Children and the elderly are at higher risk for severe disease. Antibiotic resistance is of increasing concern. A study recently conducted in Melbourne found that 28% of VTEC strains isolated from healthy babies, who had neither contact with antibiotics nor had gastrointestinal symptoms for at least two weeks prior to the specimen being taken, were resistant to one or more of the antibiotics tested.

Control measures

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

Control of case
Treatment is generally supportive, particularly maintenance of hydration. The role of antibiotics in the management of VTEC is unclear and there is some concern that they may 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, child care workers and health care workers must not work until symptoms have stopped and two consecutive faecal specimens taken at least 24 hours apart are negative for VTEC.

Children must not attend school or child care until diarrhoea has ceased. Any ongoing exclusion is at the discretion of the Secretary of the Department of Human Services.

Control of contacts
The diagnosis should be considered in symptomatic contacts. As for cases, work and school exclusion apply to contacts with diarrhoea.

Control of environment
Environmental surfaces exposed to infectious material should be thoroughly cleaned. Implicated food should be destroyed and contaminated water sources treated.

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

Outbreak measures

A single case of EHEC or HUS is potentially indicative of an outbreak. Search for other cases and identify persons at risk of infection. A source of infection should be sought for all cases of EHEC and HUS. Obtain detailed food and environmental exposure histories from cases. Collect samples of potentially implicated food and send to the Microbiological Diagnostic Unit for analysis. Antibiotic prophylaxis has neither been proven to be efficacious nor safe for the prevention of secondary cases during VTEC outbreaks.

Refer to the Department’s Guidelines for the investigation of gastrointestinal illness for more detailed on the investigation and management of outbreaks.

Additional sources of information

• Bettelheim, KA, Hornitzky, MA, Djordjevic, SP, Kuzevski, A 2003, ‘Antibiotic resistance among verocytotoxigenic Escherichia coli (VTEC) and non-VTEC isolated from domestic animals and humans’, J Med Microbiol, vol. 52, pt 2, pp. 155–62.
• Karmali, MA 1989, ‘Infection by verocytotoxin-producing Escherichia coli’, Clinical Microbiological Review, vol. 2, no. 1, pp. 15–38.
• Subcommittee of the PHLS Advisory Committee on Gastrointestinal Infections 2000, ‘Guidelines for the control of infection with Vero cytotoxin producing Escherichia coli (VTEC)’, Commun Dis Public Health, vol. 3, no. 1, pp. 14–23.