As 24 patients are being contacted on Teesside amid fears that surgical instruments used on a patient with CJD may have spread the incurable brain disease, Health Correspondent Barry Nelson presents a question and answer guide to the current crisis.

Q: What was the patient in hospital for and is he/she aware they have Creutzfeldt-Jakob Disease (CJD)?

A: The hospital has contacted the patient and relatives. No more details can be given because of confidentiality rules.

Q: Will the patient's family have to be tested?

A: No. There is no standard blood test which can be carried out to detect CJD.

Q: How do you test for CJD and what is the incubation period?

A: Doctors usually test for this disease by taking a small biopsy - tissue sample - from the brain. The incubation period for sporadic CJD is 20 years plus.

Q: What is the difference between this type of CJD and variant CJD (sometimes known as the human version of BSE)?

A: Sporadic CJD tends to occur spontaneously, although how people get it remains uncertain. It accounts for 85 per cent of all cases and should not be confused with variant CJD, which is often linked to contaminated meat.

Variant CJD patients tend to be younger, whereas classic or sporadic CJD is more common in late middle-aged people. Variant CJD also has a distinctive sponge-like appearance in the brain tissue which differs from the classic type.

Q: How rare is it?

A: Sporadic CJD is extremely rare and affects about one person in a million.

Q: What causes sporadic CJD?

A: The cause of most cases of sporadic CJD is not known. In the past, a small proportion of cases have been linked to medical procedures, when it is thought that the disease has been spread by shared instruments.

The majority of cases internationally are linked to the now banned use of human growth hormone extracted from patients who had CJD.

Q: How do you make a positive diagnosis of CJD?

A: Consultants will suspect CJD if the patient's behaviour and medical history point to such a diagnosis. However it is only possible to be completely sure by carrying out a brain biopsy (taking a sample of brain tissue and analysing it) or by carrying out a postmortem.

Q: Why is it thought that instruments used on a patient with CJD may spread the disease to other patients?

A: Prion proteins, which are believed to spread CJD, are resistant to conventional methods of decontamination, cleaning and sterilisation of surgical instruments, creating a theoretical risk that the disease could be spread if the instruments are re-used.

Q: What has been done to prevent the spread of CJD through shared instruments?

A: Guidance aimed at reducing the rare risk of cross-infection was first introduced in the NHS in the 1980s. Further guidance was issued in 1999. Among the measures introduced, any surgical instruments used on patients suspected of having CJD of any type should be quarantined pending confirmation of a diagnosis. High-grade washing and steam cleaning of instruments is being introduced at all NHS hospitals. In 2000, an investment of £310m was allocated to upgrade cleaning of surgical instruments. Plans were drawn up for each hospital. South Tees trust was classified as "amber" (ie standards are acceptable) last year.

Q: The Department of Health has given trusts millions of pounds to review their decontamination and tracing systems. Why has the Trust not initiated this and wouldn't this have prevented this from happening?

A: The trust has plans to transfer all decontamination procedures from Middlesbrough General Hospital to The James Cook University Hospital, where state-of-the-art sterilisation equipment has been installed. The trust is also introducing tracing, where each piece of kit will have unique identifiers engraved on them.

Q: Why are disposable instruments not used in brain operations as a matter of course?

A: Disposable instruments for neuro-surgery are currently not available. Hospitals always have spare sets if they are needed.

Q: Why did the South Tees trust send a sample to the CJD surveillance unit if CJD was not suspected?

A: A trust spokesman says one of the pathologists wanted to rule CJD out, rather than confirm it.

Q: Why did it take so long for the hospital to contact patients affected by the alert? The diagnosis was made in August.

A: Trust officials say as soon as a positive diagnosis was made the hospital followed the CJD surveillance unit guidance, which included the withdrawal of suspect instruments. It was not until Tuesday afternoon that they were informed by the CJD unit that they should contact the patients.

Q: How can the hospital be sure there are 24 patients affected, and not more?

A: All of these patients had their operations with the equipment used on the original patient before hospital bosses were notified of the diagnosis of CJD and quarantined the equipment.

Q:What equipment has been quarantined?

A: The hospital withdrew several drills, craniotomy sets and general medical sets used in the theatre as a precaution as soon as the diagnosis was confirmed. The total cost of this equipment is £90,000.

Q: Have any operations been cancelled as a result?

A: No operations have had to be postponed as a result because replacement equipment recently delivered to the Trust is now being used.

Q: What procedures do hospitals follow if there are suspicions that a patient has CJD?

A: Hospitals follow strict guidelines when a patient is suspected to have CJD. All medical instruments would be quarantined immediately after use and the surgeon would wear goggles.

Q: Have there been other cases of CJD at the South Tees trust?

A: Trust bosses say they have had one other case of sporadic CJD at the hospital around 20 years ago.

Q: Have there been problems with disposable instruments in other specialties apart from neurosurgury?

A: Last year a young woman patient died after an operation at Middlesbrough General Hospital to remove her tonsils went wrong. This led to all tonsil operations using disposable instruments being put on hold and a return to using non-disposable instruments. Department of Health officials decided that the risk to patients from disposable instruments was greater than the theoretical risk of transmitting CJD through shared instruments.

Q: Is anything being done to detect CJD proteins on surgical instruments?

A: A new method to detect CJD proteins has been developed by scientists at Southampton University. It works by using fluorescent and white light to detect minute amounts of the protein on the surface of surgical instruments. Combined with stricter sterilisation methods being introduced in UK hospitals, the new system should help to minimise the risk of cross-contamination during surgery.