Vancomycin-resistant staphylococcus aureus (VRSA) is particularly dangerous if caught by those who are already weak or ill.

Most antibiotic-resistant infections can be treated using vancomycin, a well-established, powerful drug used only as a last resort by doctors.

However, VRSA appears to have developed some level of immunity to even this final line of defence.

The first victim, in February this year, was a middle-aged woman suffering from cancer who died after two weeks of antibiotic treatment failed to halt the virulent bacteria.

But Hong Kong's microbiologists have now confirmed that three more people have died from the bug.

They are worried by the fact that the Hong Kong strain of VRSA appears even more resistant to antibiotics than those strains which have emerged elsewhere.

Only a handful of countries have found VRSA strains in patients - the first was Japan in 1997.

Cases in Scotland

The UK had two confirmed cases in a hospital in Glasgow. One woman died, although it was not made public whether VRSA, or her original condition, was the prime cause.

Many hospitals have hand-washing regimes to control infection

The other patient carried the VRSA bug without ever becoming ill as a result - it was detected by routine checks at Glasgow Royal Infirmary.

Ho Pak-leung, from the University of Hong Kong, said: "There should be more cautious use of antibiotics to delay the emergence of more and more superbugs."

He said the overuse of antibiotics in Hong Kong had been contributory to the particularly resistant strain that had developed.

World-wide, scientists blame the inappropriate prescribing of the drugs, for viral illnesses such as flu, and in agriculture to encourage the growth of livestock.

The standard 'superbug'

Antibiotic-resistant strains of bacteria, referred to as MRSA, or Methycillin Resistant Staphylococcus Aureus, are relatively common in UK hospitals.

Infections can lead to patient deaths, even though antibiotics such as vancomycin can prove effective.

Many people carry the bacteria without ever displaying symptoms - these generally only arise in certain patients whose health is vulnerable during serious illness or following surgery.