Twenty-four patients who are at theoretical risk of contracting an incurable brain disease are being contacted by South Tees Hospitals NHS Trust today.

The patients were operated on with the same surgical instruments used on a woman patient who was diagnosed as having Creutzfeld Jacob Disease.

But officials at the Teesside trust have stressed that all official guidelines were followed and they did not know that the woman had CJD until after a brain biopsy was analysed - several weeks after the operation.

In a statement the South Tees trust said the confirmation of a single case of sporadic CJD - which is different from variant CJD, the human form of mad cow disease - was made 20 days after a biopsy was carried out to confirm what was thought to be a different disease.

The operation took place on July 19 and as soon as the diagnosis of CJD was confirmed on August 8 the surgical instruments used on the patient were placed in quarantine and taken out of service.

Dr Paul Lawler, medical director at South Tees Hospitals NHS Trust, denied reports in The Guardian newspaper that the hospital did not follow advice that equipment used on confirmed or suspected cases of any type of CJD should not be used again.

"Once sporadic CJD was diagnosed we followed the procedure set down by the CJD incidents panel. CJD was not suspected in this patient at the time of the operation. It was due to the diligence of one of our pathologists that a sample of tissue was sent to the CJD surveillance unit - to rule CJD out rather than confirm it," said Dr Lawler. While 29 patients were operated on with the suspect instruments, scientists say only 24 are at risk.

The helpline issued by the trust is: (01642) 854944. .