Conservative leader Michael Howard has claimed that the number of deaths from hospital infections is greater than the number of road deaths in Britain each year.
The Conservative health manifesto, Action on Health, says: "You are more likely to die from a disease picked up in an NHS hospital than to be killed on Britain's roads."
It adds: "Rates of the MRSA superbug have doubled since 1997."
HOSPITAL DEATHS: THE FACTS
The difficulty in assessing the validity of this claim is that there are no official figures for deaths from hospital infections.
The figure quoted by the Conservatives - 5,000 deaths from hospital-acquired infections - is an estimate originally made in 1995 and repeated by the National Audit Office in 2000 as part of its report into improving patient care.
This was said to be "still the best estimate available" when the report was updated in 2004.
This figure is substantially higher than the number of road deaths in England and Wales, which were 3,508 in 2003.
There are figures on hospital infection rates which show that in 2002, 9% of patients in England - or about 100,000 people - acquired an infection in hospital.
This is broadly similar to estimated hospital infection rates in other developed countries, with the US at 5-10%, France at 6-10%, and Australia at 6%.
MRSA: THE FACTS
Some confusion has arisen from the Tories' juxtaposition of MRSA infection rates with hospital death rates.
The increase in MRSA infections in hospitals is a real concern.
The number of cases of MRSA has been rising sharply - from 2,422 in 1997 in England and Wales to 7,684 in 2003/4 in England alone - although the number showed a big jump in 2001 when the government introduced a mandatory reporting scheme for the infection.
However, official figures show that only about 15% of reported cases result in death.
The total number of deaths reported in England and Wales in which MRSA was mentioned as a cause has risen in the same period from 389 to 955. But MRSA was cited as the underlying cause of death in only one-third - 321.
In March, a press release from Health Secretary John Reid said that "MRSA cases were the lowest ever recorded as NHS actions begin to take effect."
This referred to the fact that in the half-year from April-September 2004 the number of reported MRSA cases in England fell to 3,519, compared with 3,744 for the same period the previous year.
However, since mandatory recording only began in 2001, there are just three full years of comparable data.
WHAT THE THREE MAIN PARTIES SAY
Labour has set a target of cutting MRSA infection rates by half in the next three years.
The Conservatives are focusing on hospital cleanliness as one of their top five election priorities, and say they will give matrons new powers to close infected hospital wards and operating theatres.
The Liberal Democrats blame the Conservatives for the initial rise in MRSA because they made hospitals contract out their cleaning, causing a fall in standards.