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Escherichia coli 0157

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VOL: 96, ISSUE: 46, PAGE NO: 42

Sandra Stilling, RGN, is infection control/wound care nurse, West Cumbria Health Care NHS Trust

Many strains of the bacterium Escherichia coli live in the bowel of animals and humans causing no harm. However, some strains are pathogenic and cause gastrointestinal disease and complications (The Pennington Group, 1997). E.coli 0157, sometimes referred to as VTEC (Vero cytotoxin-producing E.coli) produces toxins that can cause human illness.The organism is extremely virulent requiring less than 50 organisms to cause illness in humans (Dundas and Todd, 1999).

Many strains of the bacterium Escherichia coli live in the bowel of animals and humans causing no harm. However, some strains are pathogenic and cause gastrointestinal disease and complications (The Pennington Group, 1997). E.coli 0157, sometimes referred to as VTEC (Vero cytotoxin-producing E.coli) produces toxins that can cause human illness.The organism is extremely virulent requiring less than 50 organisms to cause illness in humans (Dundas and Todd, 1999).

The incubation period for E.coli 0157 is usually three to four days (PHLS, 1997b).Abdominal cramps and non-bloody diarrhoea are classic initial symptoms. Vomiting can also be a clinical feature. In 70% of cases diarrhoea will subsequently become bloody (Mead and Griffin, 1998; Coia, 1998a)

The most severe systemic complications are haemolytic uraemic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP) (Dundas et al, 1999). In these conditions, toxins produced by the E.coli are absorbed and damage the lining of the capillaries in the kidney. This causes localised clots to form in the blood vessels, resulting in impaired kidney function. Other organs which can be affected, particularly in elderly people, are the heart, brain and pancreas.

The mortality rate from these complications is 5% in children and much higher in older people. Neurological symptoms of HUS and TTP can occur in 25% of cases. These usually present as drowsiness, cerebral vascular accidents, seizures or coma (Dundas and Todd, 1999).

Gastrointestinal complications include rectal prolapse, ischaemic colitis and large bowel perforation (Dundas and Todd, 1999).

Incidence
E. coli 0157 was first identified as a human pathogen in the USA in 1982, when two outbreaks were associated with the consumption of hamburgers from a fast-food chain (Dundas et al, 1999). Since then, outbreaks have occurred globally.

Between 1981 and 1997 the UK incidence of E.coli 0157 significantly increased, with over 80% of cases being sporadic (PHLS, 2000). Scotland has a higher incidence than elsewhere in the UK (Coia, 1998a; Dundas and Todd, 1999).

An outbreak occurred in central Scotland in November and December 1996, resulting in 496 cases. Eighteen people died and 127 people were admitted to hospital, of whom 13 required dialysis treatment (The Pennington Group, 1997).

In March 1999, West Cumbria had the largest outbreak in England so far. Sixty-one people were affected, of whom 12 adults and 16 children were admitted to hospital. Three children required dialysis. The source was milk from a local farm.

Transmission
Infection with E. coli 0157 is more common in the summer and autumn (Coia, 1998a). Healthy cattle are a major reservoir, with the organism existing in manure, water troughs and other farm areas (Dundas and Todd, 1999). The organism can survive for more than 150 days in soil and 90 days in cattle faeces (PHLS, 1997a).

A variety of foodstuffs have been associated with outbreaks, including ground beef, salami, unpasteurised milk, cooked meats, fruits and vegetables and unpasteurised apple juice (Mead and Griffin, 1998). Vegetarians and vegans are therefore not exempt from risk. Food-borne spread usually occurs owing to a lapse in food handling practices or contamination of ready-to-eat/drink products (PHLS, 2000).

There have been outbreaks among children who have visited open farms and, after handling or stroking animals or having contact with soil, have put their unwashed hands in their mouths (PHLS, 1997b).

Person-to-person transmission has occurred in day care and long-term care facilities (PHLS, 2000). This population is at particular risk because they are often elderly, require a high degree of hands-on care or may lack of awareness of the importance of personal hygiene. Occupationally-acquired exposure has also occurred among nurses and laboratory workers (Coia, 1998b). Secondary spread to household contacts can occur.

Certain groups of people do pose a significant risk of transmitting the infection (PHLS, 2000), (Box 1). Negative stool specimens, at least 48 hours apart, will be required before these people can return to work or school.

Prevention
The dictum that prevention is better than cure is particularly applicable to E.coli 0157, with good hygiene being the key preventive message (PHLS, 2000). This can be achieved by:

- Thorough handwashing with soap after any contact with animals, if hands become soiled with animal faeces, before handling or eating food and after using the toilet;

- Regular and frequent cleaning of toilet/changing areas with detergent and water and of shared toys;

- Not eating while attending to animals;

- Ensuring sufficient hand-washing facilities are available at open farms, along with the supervision of children;

- Educating staff in the importance of good hygienic practices. In some care facilities, hand-washing will need to be supervised to ensure compliance.

Management
Diagnosis is made usually by isolating the organism from a stool specimen. If the stool culture is negative and the diagnosis is strongly suspected (from a clinical assessment), a stool specimen may be sent to the laboratory for gene probing.

Prevention of spread is a key factor when managing E. coli 0157 in a health care setting and the following points must be addressed:

- Ideally patients should be nursed in a single room with its own toilet facility. This will be dependent on a risk-assessment as it may be inappropriate or impractical;

- Enteric precautions must be maintained (Box 2). Handwashing is essential at all times;

- Ensure all those with symptoms wash their hands after using the toilet and before eating;

- Offer explanations regarding the infection and its management to both patients and visitors to alleviate concerns or anxieties. Fact sheets may be used to consolidate verbal information (Table 1).

Treatment for E.coli 0157 infection will depend on symptoms (PHLS, 1997b; Mead, 1998) but may include intravenous fluid replacement and careful monitoring and observation for any complications, such as signs of HUS or TTP.

Antimotility drugs such as loperamide and codeine phosphate are contraindicated and antibiotics are not recommended (Dundas and Todd, 1999; PHLS, 2000). Patients must be closely monitored for signs of dehydration, pallor, sudden weight gain or oliguria. Children under five and elderly patients will require monitoring of blood smears, haematocrit levels and urinalysis results.

Conclusion
An understanding of the mode of spread of E.coli 0157, the importance of good hygiene and how and when to wash hands could significantly reduce the risk of spreading this dangerous pathogen.

RESOURCES
HUSH (UK E.coli support group)

Steve Nash

79 Hayes End Road

Hayes

Middlesex UB4 8EG

Tel: 0800 731 4679

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