A potent strain of superbug that is rife in America is emerging at an increasing rate in Britain, doctors say.

A growing number of patients are being treated for infections with Panton-Valentine leukocidin-positive (PVL) MRSA, which can attack the immune system of healthy adults and children.

The highly infectious bacteria spread through the community and are not confined to hospitals, but have previously been found only in isolated cases in Britain.

The Health Protection Agency said that only seven deaths in England and Wales had been associated with PVL-positive MRSA in the past two years. But Marina Morgan, from the Royal Devon & Exeter Foundation NHS Trust, said that if community strains spread as they had in the US, many more with unsuspected MRSA infections would be admitted to hospitals.

“The new community-associated MRSA strains appear to be more virulent and more easily spread between people,” she said. “When doctors finally realise the infection is MRSA, by the time patients get the correct treatment it may be too late.”

MRSA, or methicillin-resistant Staphylococcus aureus, is a common bug, carried by millions of people, that has mutated to become immune to many antibiotics. Symptoms range from minor infections in the skin and soft tissues to a form of pneumonia that can kill in 24 hours. Dr Morgan said that this type of pneumonia would kill more than 60 per cent of otherwise healthy young, fit people. Community-acquired MRSA (CA-MRSA) is now well established in America, where it triggers about one in ten MRSA cases and is a common cause of childhood infection.

One in five infected patients requires hospital treatment, and doctors are worried about the same pattern being repeated in Britain.

The new strains appear to attach themselves to damaged skin and air-ways more easily than hospital MRSA, and they multiply at a faster rate. The PVL toxin they produce kills white blood cells, an essential part of the body’s immune system, although researchers believe that there are other reasons for the virulence of CA-MRSA.

Dr Morgan said: “These community-associated versions have been found in people with few, if any, reasons to have MRSA. They haven’t recently been in hospital, or are not looking after or living with people with MRSA.”

A spokesman for the HPA said that PVL-MRSA was “more toxic than other strains of MRSA”, but it could be treated with antibiotics.

Dr Morgan is due to spell out the scale of the problem today at the Federation of Infection Societies Conference, at the University of Cardiff.

The meeting will also hear of a threat from bacteria that can destroy common antibiotics, including penicil-lin. The bugs, which include a strain of Escherichia coli (E. coli), are spreading out of hospitals into nursing homes and communities throughout Europe. They produce enzymes called extended spectrum beta-lactamases. Between 2003 and 2004 a severe outbreak of bladder infections was caused by E. coli that made one of the enzymes.

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