Fears that a new superbug is taking hold in Britain emerged yesterday after a Royal Marines recruit was found to have died suddenly from an infection with no known cure.
Richard Campbell-Smith, 18, died three days after the lethal toxin, which is linked to MRSA, entered his body through a scratch in his leg.
Panton-Valentine Leukocidin (PVL) is so virulent that only a quarter of people in whom the infection spreads to the chest survive.
The coroner investigating Mr Campbell-Smith's death was so worried about an outbreak that she is writing to the chief medical officer.
An expert told the Exeter inquest that she had seen two examples in nine weeks and wanted to alert the public and doctors to the dangers of the disease, which has been recorded in America, France and Australia.
Dr Marina Morgan, a microbiologist, said: "It is the worst bug I have seen and people really need to know about it.
Mr Campbell-Smith was 28 weeks into his 32-week induction at the Commando Training Centre, at Lympstone, Devon, when he died.
He and other recruits had spent the week in rigorous exercise and he scratched his legs while running on Oct 31 last year.
Dr Morgan said it was thought the disease had been eradicated in the 1950s but it could be coming back as antibiotics lost their effectiveness because of overuse.
She said it usually attacked people under 40 and often occurred alongside MRSA.
"It multiplies very quickly: one bug will multiply into 17 million within 24 hours.
"Signs include pneumonia, coughing up blood and very high temperatures but not everyone will look for it.
The Department of Health said it was aware of cases of PVL and the Health Protection Agency was monitoring the situation.