Hospital infections caused by MRSA 'superbugs' have leapt by 50 per cent in just one year, unpublished Public Health Laboratory Service figures show.

Only four years ago, MRSA incidence in inpatient blood samples was well below 10 per cent. But new PHLS data shows that certain types - the so- called 'epidemic' strains eMRSA-15 and eMRSA-16 - are spreading rapidly.

More than 30 per cent of Staph. aureus infections in hospitals are now likely to be resistant to the standard first-line antibiotics such as flucloxacillin.

In two years' time, the data indicates, these antibiotics may be useless, sending the costs of treatment soaring and putting hospitals at risk of general MRSA outbreaks and ward closures.

Staph. infections will have to be treated with vancomycin - which is expensive to administer and can have unpleasant side-effects.

The finding lends urgency to a National Audit Office study launched this month to find the most cost-effective ways of fighting hospital-acquired infections. The Department of Health is believed to have asked for the NAO investigation after seeing the results of a comprehensive PHLS study of the costs such infections.

The laboratory's report was completed at the end of last year but is still confidential. The NAO's findings will not be released until mid- 1999.

About one in ten inpatients gets HAI. Up to a fifth of these are caused by Staph. aureus.

Each case can cost more than pounds3,000 to treat - and considerably more if the infection is antibiotic-resistant.

According to Rosalind Plowman of the London School of Hygiene and Tropical Medicine, who collaborated on the PHLS study, the highest cost of an outbreak is in closing and disinfecting wards and setting up isolation areas.

One five-week outbreak cost an estimated pounds30,000, she said. Another cost more than pounds400,000 over two years.

It is the resulting pounds170m total annual health service cost that has prompted the NAO investigation.