Q&A: E. coli O157
What is E. coli?
E. coli or Escherichia coli to give it its full name is a common bug which is present in the environment.
Mostly it helps people to stay healthy, but it can also cause illness as well.
O157 is the most serious type. Symptoms can range from mild diarrhoea to haemorrhagic colitis - a combination of severe abdominal cramps and blood in the stools.
Most people will shake it off within a few days, but children and older people can be particularly hard hit.
A small proportion may eventually develop serious kidney damage which requires dialysis treatment or a transplant.
How are people infected?
There are three basic methods of infection - through contaminated food, touching animals or from the environment.
Animals - and cattle in particular - carry this strain of E. coli in their gut. It does not seem to adversely affect them, but can be passed on to humans by eating undercooked meat.
It can also be present in their faeces and, as a result, passed on to humans who come in direct contact with them.
The bacterium is also quite robust which means it can live in the environment - that is to say on things such as railings and gates - for weeks and perhaps months.
People then touch these surfaces and when they eat food it gets into their body orally.
Undercooked meat used to be the primary source of most O157 infections.
But food production is generally considered to have improved its safety standards over the past 10 years and this is now becoming a less important - albeit still significant - source of infection.
How common are E. coli infections?
There are more than 20,000 reports of E. coli infections each year.
Many of these are in hospital and are among elderly patients.
But cases of O157 are much rarer. In England and Wales, there are only about 800 cases a year.
There tend to be about three to four outbreaks a year and these tend to affect only about 10 people.
In the worst recorded outbreak, 20 people died in Scotland in 1996-97 after attending a church lunch in Wishaw, Strathclyde.
Following the Scottish outbreak, the British government set up a commission to look into the issue of food safety.
What can be done to prevent such infections?
The two best - and most simple - steps are good hand hygiene and cooking and preparing meat properly.
Raw and cooked meat should always be kept apart during food preparation and people should always clean their hands after handling raw meat.
For direct animal-to-human transmission or indirect infection via the environment, good old soap and water is the best defence.
While the bacterium is pretty good at surviving in the environment, it can be relatively easily killed by washing hands, and cleaning surfaces with disinfectant.