As CJD survives current sterilisation procedures, hospitals may have to consider implementing more expensive alternatives, reports Sally Dawson

an inquiry was ordered in late october after it emerged that 24 hospital patients had been exposed to the fatal pathogen CJD.

This was no ordinary hospital blunder - as medical guidelines were actually followed - and it could happen again at any time.

The incident came to light after a woman patient who underwent a brain-biopsy at Middlesborough General Hospital was later diagnosed with sporadic CJD, which was not suspected at the time.

Unlike viruses and bacteria, prions - the infective agent which causes the fatal neurodegenerative condition Creutzfeldt-Jakob Disease - can survive the sterilisation process. But under current policy, surgical instruments are only discarded after an operation if a patient is suspected to be suffering from the disease.

The sporadic form of CJD is not connected to new variant CJD - the disease linked to eating contaminated meat - and can take up to 30 years to incubate. However all types of CJD can survive current sterilisation procedures.

The chief executive of the hospital trust, Bill Murray, expressed his deep regret at the incident: "Every patient will be allocated a named person at the trust who will fully support them for as long as they feel they need it and we will be working with them to look at any theoretical risk - if any - they have."

Although the risk is small - and depends on the type of procedure they had - there are five documented cases of patients being infected in such a manner worldwide.

The risk of infection from contaminated instruments is believed to fall with every successive patient on which they are used. The most hazardous types of surgery are thought to be on the tonsils or brain, although the placenta, cerebrospinal fluid, lymph nodes, intestines, appendix, spleen and eye are also suspect.

Although current hospital sterilisation procedures are effective, in killing viruses and bacteria, prions can not only survive temperatures of 100 degrees Celsius, but also cannot be guaranteed to be removed by vigorous scrubbing.

In its report, Infection Control Guidelines for Transmissible Spongiform Encephalopathies, (published in 1999) the World Health Organisation recommends three alternative methods thought to be more effective in killing CJD. These methods involve different variations of soaking the instruments in solutions of 1N sodium hydroxide or NaOH, or sodium hypochlorite, for one hour, followed by heat treatment in a gravity displacement autoclave - a procedure whereby air is displaced by steam through a port in the bottom of a sterilisation chamber - at 121 degrees Celsius for 30 minutes to an hour followed by a "routine" sterilisation process.

It is essential that instruments be kept moist until decontamination and cleaned as soon as possible to "minimise drying of tissues, blood and body fluids onto the item".

However there is a limited range of materials that can be subject to this process as some - such as gold-plate, glass and aluminium - can be corroded by sodium hypochlorite. Heat-sensitive instruments and surfaces can be washed in 2N NaOH, or undiluted sodium hypochloride, for one hour and then washed in water.

The NHS is faced with two alternatives to its current sterilisation procedures: either it can implement the more costly processes of sterilisation outlined above or it can dispose of its instruments. These choices must be balanced by the statistical likelihood of a patient coming into contact with infective material. If the risk is low, the cost of implementing the new procedures may be disproportionate.

If, as some experts predict, many more people will develop nv-CJD as a result of their exposure to BSE infected beef during the late 80s and early 90s, then the cost of more stringent sterilisation procedures may be justifiable, saving both money and lives in the long term. As, ultimately, the WHO report states: "The safest and most unambiguous method for ensuring that there is no risk of residual infectivity on contaminated instruments and other materials is to discard and destroy them by incineration."