It is resistant to common antibiotics, but can be treated with a second-line antibiotic, vancomycin.

United Christian Hospital chief executive Dr Tse Chun-yan said five clusters of infection - defined as four or more cases in a ward within two weeks - had been found between March and June.

Two were in surgical wards, two in geriatric wards and one was in an orthopaedic ward.

'When a case is identified, we isolate the patient to prevent it from spreading. The transmission is mainly through contact,' Dr Tse said.

'But if we have clustering, in addition we do a screening of all patients in the ward and all staff working there.' A small percentage of staff and patients had been 'colonised' by the bacteria, which infected them but caused no illness.

All has subsequently been treated.

A Hospital Authority spokesman said almost all of the Haven of Hope's 41 MRSA patients, diagnosed between April and July, were infected before they were transferred from other hospitals.

Only three acquired the infection in the hospital.

The authority kept no central record of such infections, but relied on individual hospitals to notify it if they had a serious outbreak.

'Numbers are irrelevant to the situation,' the spokesman said. 'They monitor the situation.' Tuen Mun Hospital consultant microbiologist Dr Que Tak-lun said the infections caused problems in hospitals worldwide, particularly in Hong Kong, Australia and Britain.

'Staphylococcus aurus is an organism - it means golden-yellow bacteria in the form of grapes,' Dr Que said.

'It was one of the most common pathogens in hospitals before we had antibiotics, half a century ago.

'The mortality is pretty low. I would think it is well below five per cent. Even if it causes infection, it usually responds to treatment.'