The E.coli bacterium can cause serious infection
Fourteen people have been affected by the latest outbreak of the E.coli bug, in Leeds. How harmful is the bug?
The E.coli 0157 bacterium, normally found in the intestines of people or cattle, is particularly harmful to young children and pensioners.
In the worst recorded outbreak, 21 people died in Scotland after attending a church lunch in Wishaw, Lanarkshire, in 1996.
The strain of the bug - which can be passed on by eating infected food and liquid - first appeared in Britain in the 1980s.
It is found naturally in the gut of animals including cattle, sheep, deer and goats.
Simply carrying the bacterium will not normally cause an animal any harm or illness.
However, if humans come into contact with it, the toxins produced can cause illness such as diarrhoea or abdominal cramps.
Some patients suffer from a complication, hemolytic uremic syndrome (HUS), which kills red blood cells and can cause kidney failure.
In some cases the illness can be fatal.
People can become infected from contaminated foods, direct contact with animals or contact with animal faeces.
The full name of the strain is Verocytotoxin-producing E. coli, or VTEC. Fewer than 100 of the tiny E.coli organisms can cause illness.
Before the 1996 Scottish outbreak, the worst recorded outbreak was in Canada in 1982 when 19 pensioners from a nursing home died.
According to the Health Protection Agency, the incidence of the 0157 strain is variable throughout the UK, with the highest rate in Scotland.
In England and Wales between 1995 to 2000, there were 106 general outbreaks. Provisional figures say that there were 15 general outbreaks in 2001.
Recent incidences in the UK include one at a Scottish nursery school in Dunfermline, Fife, in May.
The nursery was shut for nearly five weeks and five toddlers were treated in hospital although they have been since released.
Professor Hugh Pennington is investigating the 2005 outbreak
Another outbreak occurred in May in Law, Lanarkshire, when at least four people were diagnosed with the infection. The outbreak was linked to a local butcher.
A 2005 outbreak in south Wales killed five-year-old Mason Jones, and affected more than 150 others, mainly school children.
The man leading a public inquiry into the outbreak, Professor Hugh Pennington, has pledged to leave "no stone unturned".
Following the deaths in Lanarkshire in 1996 the British government set up a commission to look into the issue of food safety.
Experts at Britain's Communicable Disease Surveillance Centre recommend keeping raw and cooked meat separate and ensuring all meat is properly cooked.
Health experts also advise that people should always wash their hands after handling raw meat and other food, and should not touch manure.