The MRSA superbug has evolved into 'fitter' strains which could prove even more resistant to treatment, a leading scientist warned on Tuesday.
Professor Hajo Grundmann, a world expert in infectious diseases, said MRSA in hospitals is already 'out of control' in many countries.
But the emergence of stronger and more virulent strains could prove potentially 'explosive'.
MRSA - or methicillin resistant staphylococcus aureus - has already become resistant to most common antibiotics, making it difficult to treat with drugs. Once it gets into the body, through wounds or medical tubes, it can cause an infection that could kill someone already weakened by illness.
In Britain, it is estimated that MRSA and other infections such as clostridium difficile kill up to 5,000 patients every year, despite a Government drive to clean up hospitals.
Other estimates claim the real figure may be twice as high. In England alone, 300,000 patients pick up an infection in hospital every year.
According to Professor Grundmann, between two million and 52million people worldwide could be carrying the superbug.
MRSA is now so widespread that in many parts of the world it is the most commonly identified bacterium which is resistant to antibiotics.
Writing in The Lancet, scientists from the National Institute for Public Health and the Environment, in Holland, said that MRSA is regularly found in Europe, North and South America, North Africa, the Middle East, and East Asia.
The MRSA situation in hospitals could become 'explosive'
Professor Grundmann, who is scientific co-ordinator of the European Antimicrobial Resistance Surveillance System, said rates of MRSA are beginning to rise in Scandinavia and the Netherlands, where levels had been low in the past.
This indicates that new strains are spreading which are resistant to traditional treatment.
He added: 'If the new community-acquired MRSA clones are sufficiently fit to sustain endemic levels by transmission into the community, the MRSA situation in hospitals, which still remains out of control in many countries, could potentially become explosive.
'The onus is on healthcare authorities to develop not only surveillance systems that are able to monitor the clonal dynamics of MRSA over wide geographical areas, but also to provide the resources for early recognition of MRSA carriers through rapid screening.'
This year, a survey revealed that three times as many British patients were worried about catching MRSA as about delays in treatment.
The Office for National Statistics said that between 2003 and 2004, the number of deaths in which MRSA was mentioned on the death certificate rose by 22 per cent.
The MRSA infection was also six times more likely to be mentioned on the death certificates of patients in NHS hospitals and care homes than those who died elsewhere.
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