It is four times more deadly than MRSA and showing signs of resistance to one of only two drugs able to combat it.
Now research has revealed that hospital superbug Clostridium difficile (C.diff) is responsible for 6,500 deaths in British hospitals each year - the equivalent of one person dying every hour.
These are the shocking findings of a Panorama investigation, which found that in the UK in the past year the bug had claimed the lives of ten times the number of hospital patients over the age of 65 than anywhere else in the world.
Sally Magnusson, who made the programme, said: 'Thousands of families are in exactly the same position - angrily grieving for relatives who went into hospital with one thing, only to be struck down by a superbug in the wards.
'It is a frightening picture. And hospitals which may already be struggling with overcrowded wards, and the effort to implement Government targets, are finding themselves under pressure.'
Professor Richard James, who runs a Nottingham University centre investigating hospital infections, described the findings as evidence of an 'extraordinarily bad situation'.
He said: 'More than 50 per cent of hospital trusts have a rate of infection that's more than ten times that of any other country.'
His remarks are based on a draft report to the Department of Health from the influential steering group on healthcare-associated infection.
However, last week the Department of Health said that the battle against such superbugs was being won, claiming that C.diff infections in England had fallen by eight per cent between October and December 2007.
But according to the Panorama investigation, the way cases are counted has changed, and experts calculate that the real figure is actually between 16 and 35 per cent higher than the official rate.
Among the most serious concerns of scientists is that these figures reflect a mutation and strengthening of the superbug. Only two antibiotics can treat C.diff, and research has revealed that it has developed partial resistance to one of them.
Ironically, measures brought in to combat MRSA in hospitals are actually contributing to the spread of C.diff.
According to Professor Brendan Wren, of the London School of Hygiene and Tropical Medicine, alcohol handwashes, which are now used in 94 per cent of hospitals, encourage the growth of C.diff spores.
He said: 'In the laboratory, if we want the organism to form spores, we treat it with alcohol. So the use of alcohol wipes in hospitals should be stopped for C.diff.'
Sally Magnusson added: 'The Government has contributed £16.5million to research over five years. When I suggested to Health Minister Ann Keen that, in view of the scale of the problem, this wasn't much, she mentioned a further £2.5million from NICE [the National Institute for Clinical Excellence] and said the Government would "take noteî of scientists' concerns.'
Mrs Keen said: 'NHS staff have worked hard to drive down the number of infections and I'm pleased to see significant reductions.
'To ensure that all NHS organisations take appropriate precautions to protect patients, the Healthcare Commission is now inspecting each and every trust.'
Panorama Special: How Safe Is Your Hospital? BBC1 tonight, 10.20pm