A gastroscope was used to examine patients

Letters have gone out to 449 patients who were treated at Lagan Valley hospital, Lisburn, County Antrim, using a gastroscope which had not been properly sterilised.

It is a small, flexible tube with a light and a camera lens at the end which is used to examine the inside of the stomach. It can also be used to take tissue samples for testing.

A special telephone help line has been set up and patients have been offered a meeting to discuss whether they want a blood test to establish whether they have a blood borne infection like HIV or hepatitis.

The helpline received 241 calls on Wednesday from those concerned and 107 patients were given blood tests.

The remaining patients will be tested on Thursday and Friday.

The problem came to light six weeks ago in relation to one of the hospital's five gastroscopes, after a member of staff noticed part of it was dirty.

The gastroscope, which came into use in April 2001, went through a disinfection process after each use, but one small part may not have been completely disinfected, according to management.

I understand only too well the distress this will cause to those patients John Compton Down Lisburn Trust

John Compton, chief executive of the Down Lisburn Health Trust, which runs Lagan Valley hospital, said the risk to patients was small.

Mr Compton said: "It's possible that there could be some transmission of blood borne viruses. That's the real issue for us.

"But I would reassure people, first of all, to say that the incidence of blood borne viruses in Northern Ireland is extremely low. It is at 0.2% of the population, so that's two people per thousand in a big population."

He said the trust knew on 20 April that there was a problem with a piece of equipment.

"We were not aware of the nature of the problem until some time after that.

"It took us a week until we were clear as to the nature of the problem."

He said in the ensuing period, the hospital had to trace the patients who may have been affected, and put in place a patient support system.

The trust said even if some patients had the infection, there was no guarantee that the gastroscope was responsible.

"I want to reassure people that they can have full confidence if they are to turn up to the hospital. I want to communicate a sense of deep regret that this has happened to anyone," he said.

"I understand only too well the distress this will cause to those patients."

The trust as well as the Eastern Health and Social Service Board's public health team and the Department of Health, Social Services and Public Safety have already started a full investigation.