Patients are often moved around

They warn that pressure on beds must be reduced if the bug is to be tackled successfully.

Professor Barry Cookson, from the Health Protection Agency, said UK hospitals were more crowded than anywhere else in Europe.

As a result patients were being shunted between wards - and sometimes hospitals - increasing risk of exposure.

MRSA MRSA (methicillin resistant staphylococcus aureus) first appeared in the 1960s Some strains are resistant to almost all known antibiotics Cases have increased by 600% in the past decade Cases are expected to double again in the next six years Efforts to combat it cost the NHS �1bn a year Holland's zero tolerance approach

Professor Cookson said a reduction to a bed occupancy rate of 85% would help stop the disease spreading.

The lack of single-bed units also made it more difficult to isolate patients with dangerous infections, he said.

Speaking at a briefing in London, Professor Cookson said he understood the political pressures to treat as many patients as possible as quickly as possible.

But he said while efforts to combat MRSA had focused on hand washing, overcrowding was a key issue.

In Sweden, a problem with MRSA had begun to emerge when bed occupancy rates rose to 100%.

He said: "I think we should be entering a national debate. Patients should realise that there's a certain safety level, and above that we start having problems."

He also warned that increased patient choice over which hospital to attend was likely to increase the risk of spreading MRSA.

Complex care

Professor Cookson said MRSA often infects surgical wounds, and has been encouraged by the increasing complexity and invasiveness of hospital treatment.

Modern techniques meant patients could be discharged after a shorter stay, giving them less time to pick up infections.

Very determined efforts are being made to focus action on MRSA and reduce its impact throughout the NHS. Sir Liam Donaldson

However, this meant there was also a higher risk that an infection acquired in hospital would go undetected, and develop at home, posing a risk to other patients when the host returned for a check-up.

Dr Alison Holmes, from the Department of Infectious Diseases at Imperial College, London, and Hammersmith Hospital, agreed that overcrowding was a problem.

She said it made it difficult to keep high risk patients, such as those undergoing orthopaedic or heart surgery, away from other groups.

"We're trying to stick as many patients in hospital as possible. This involves a lot of juggling and leads to an increased risk of infection."

The government's NHS Improvement Plan, which sets targets for the next five years, has pledged "significant reductions" in MRSA infection rates between now and 2010.

Sir Liam Donaldson, the Chief Medical Officer for England, said: "The NHS does run at high occupancy because it is treating many more patients and cutting waiting lists.

"In these circumstances, extra efforts have to be made to reduce the risk of infection and this is what the NHS is doing. As the infrastructure of the NHS is built up (more beds, more staff) it will be easier to control problems like MRSA.

"Very determined efforts are being made to focus action on MRSA and reduce its impact throughout the NHS."

Detailed guidance on infection control was issued to health chiefs by Sir Liam last year, pointing out the need to incorporate safety measures in bed management.