The bacterium releases spores
Experts say the bug Clostridium difficile is endemic throughout the health service.
Health Protection Agency figures show there were 55,681 cases of C. difficile infection in patients aged 65 years and above in England in 2006 - up 8% on the previous year.
What is Clostridium difficile?
It is a bacterium found in the gut of up to 3% of healthy adults and 66% of infants, where it rarely causes problems.
However, it can cause illness when its growth goes unchecked. For example, treatment with certain antibiotics can disturb the balance of "normal" bacteria in the gut, allowing C. difficile to thrive.
How does it make you sick?
It can cause no symptoms at all, mild or severe diarrhoea, or in some cases severe inflammation of the bowel which can be life threatening.
Who does it affect?
The elderly are most at risk, with over 80% of cases reported in the over 65-age group.
Patients with weakened immune systems or those who have had repeated enemas or gut surgery are also at increased risk.
Is it a "superbug"?
No. At present it can be treated relatively easily.
Unfortunately patients with diarrhoea, especially if severe or accompanied by incontinence, may unintentionally spread the infection to other patients, which may lead to outbreaks of C. difficile in hospitals.
There is also evidence that some strains have started to acquire resistance to several antibiotics in common use.
This suggests the bacterium is quickly evolving and could reach superbug status within the near future.
How can outbreaks be prevented?
The bug forms spores which means it can survive for long periods in the environment, such as on floors and around toilets, and spread in the air.
Rigorous cleaning with warm water and detergent is the most effective means of removing spores from the contaminated environment and the hands of staff, say experts.