Sterilisation 'may not kill CJD'

A survey has found that surgical instruments still have the potential to harbour CJD even after sterilisation.

Edinburgh University found every instrument they tested was contaminated with enough protein residue to pose a potential infection risk.

The researchers tested instruments taken at random from five NHS hospital trust sterile service departments.

The study, financed by the Department of Health, appears in the Journal of Hospital Infection.

CJD, a degenerative and fatal brain disease, is thought to be caused by mutated proteins called prions.

These twisted proteins are known to be able to cling to the surface of surgical instruments, and are remarkably difficult to remove by standard decontamination processes, which involve the use of detergents and super-heating.

There have been instances of patients contracting CJD from contaminated instruments during surgery.

The Edinburgh team found an average level of protein contamination of 0.2 microgrammes per square millimetre of instrument.

Unknown risk

If prions were found on so-called sterile instruments in the levels recorded in the study, that would be billions of times the dose needed to cause infection in humans.

The highest doses were found on instruments used to remove tonsils - one of the tissues known to harbour prions.

Lead researcher Professor Bob Baxter, from the University's chemistry department, said "You can never get something 100% clean, but we were surprised at how much protein there was."

Professor Baxter said measures to quarantine surgical instruments were taken if a patient was known to be at high risk of carrying CJD.

But he said that as a result of the use of contaminated blood supplies, an unknown number of people could be harbouring the disease.

"There are certainly people out there who are at risk, but we don't necessarily know who they are," he said.

The Edinburgh team has developed a more effective way to sterilise instruments, using a technique called gas plasma sterilisation.

This uses radio waves to excite the molecules of harmless gases, creating charged atoms called ions and radicals which effectively scour the surface of the instruments, breaking down traces of biological tissue and converting them to non-toxic gases.

Gas plasma sterilisation can remove prions to levels a thousand times lower than those achieved by existing methods.

Professor Baxter has recommended the widespread introduction of gas plasma cleaning to the Department of Health.

A Department of Health spokesperson said the study would be considered by an expert group.

"Although we consider the gas plasma decontamination technique interesting, it is not currently in a form that can be used in routine decontamination of surgical instruments."

RESOURCE/SOURCE: http://news.bbc.co.uk/2/hi/health/5281100.stm on Thursday, August 24, 2006.