Deadly hospital bugs have hogged the headlines in recent years.
Hospital bugs are subject to monitoring
There are many different types of infections patients can pick up in hospital, but the two that have received the most coverage are MRSA and Clostridium difficile.
Catching the infections
C. difficile is a bacterium found in the gut of up to 3% of healthy adults and 66% of infants, although it rarely causes problems.
However, certain antibiotics can disturb the normal balance, allowing the bug to thrive and causing severe diarrhoea and in some cases severe inflammation of the bowel which can be life threatening. Over 65s are most at risk.
MRSA infections occur where there is opportunity for MRSA to get into the body, such as at surgical wounds or where a catheter or needle is inserted.
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The bug can exist harmlessly on people's skins without them even knowing it, but if it infects someone who is already ill or weak, it can kill.
It is no more dangerous than many other infections, but because it has developed resistance to methicillin and other antibiotics, it is much more difficult to treat.
Combating MRSA and C. difficile
There has been a big push on ward cleaning and personal hygiene to combat MRSA.
Tactics include providing disinfectant hand-rubs and encouraging more vigilance among patients and visitors.
For C. difficile, the tactics are slightly different. Rigorous cleaning has an effect on the bug, but unlike MRSA, it is not resistant to antibiotics and can be treated relatively easily if identified quickly and the patient is not too weak.
Growth of the infections
MRSA rates hit a high in 2003-4 when there were 7,684. Since then they have been steadily falling, but not quickly enough to meet the target of halving the rate by 2008 to bring it under 4,000.
C. difficile has only come to national attention more recently. The rate of infection is still rising according to annual figures - up 8% in the last year to over 50,000.
But the latest quarterly figures suggest that the rise may have been halted.
From April to June 2007, there were 13,660 cases in patients aged 65 years or over, a fall of 7% on the same period last year.
It is the first time this has happened, but experts are waiting to see if the trend continues for the rest of the year before reaching definitive conclusions.
The National Audit Office estimates that hospital-acquired infections are costing the NHS about £1bn a year.
C. difficile is mentioned on more death certificates than MRSA.
According to the Office for National Statistics, C. difficile was linked to 6,480 deaths in 2006 and MRSA, was linked to 1,652 deaths.
But that has to be seen in the context that C. difficile is nearly 10 times more common than MRSA.