A gastroscope was used to examine patients

Over 1,300 who had undergone treatment at the Royal Victoria Hospital, Belfast, and Whiteabbey Hospital, are being advised to have blood tests.

Patients, who had undergone the procedure in Lagan Valley Hospital, Lisburn and Antrim Area Hospital, are being told they are at low risk and do not need the test.

The alert surrounds concerns that endoscopes at the hospitals were not being cleaned or disinfected properly.

Northern Ireland's Chief Medical Officer Dr Etta Campbell made the announcement on Monday.

Last week, the department said that 17 gastroscopes out of more than 1,000 used in Northern Ireland had "queries over their decontamination process".

The equipment is used to detect problems in the throat and stomach, and has to be sterilised after each use.

GASTROSCOPES Small flexible tube with a light and camera at the end Passed down patients' throats Used to check for conditions like ulcers, and to take tissue samples Must be sterilised after every use Cleaning must be done carefully with chemicals, as microscopic infections could be present

A health scare earlier this month at the Lagan Valley Hospital, prompted an audit of all such equipment.

In the first incident, more than 400 patients were offered blood tests after it emerged they had been treated at Lagan Valley hospital with a gastroscope which had not been properly sterilised.

Those patients were offered a meeting to discuss if they wished to have blood tests to establish if they had a blood borne infection like HIV or hepatitis.

Dr Campbell stressed that the risk to any one patient of a virus being transmitted because of having treatment with an endoscope was remote.

"It is important to recognise that what we are saying is that the risk to any patient through the use of any of these endoscopes is very, very small indeed," she said.

"That is an important public health message.

"What we have found has shown that there may be some minimal risk to health for some patients through the use of these and all our action has been to minimise that risk."

Jane Graham of the Eastern health and social services council said people should not cancel appointments.

"It has caused a lot of distress and people who are going forward for this procedure at the moment must be feeling anxious," she said.

"But we would certainly say to them: 'Don't cancel but go and discuss your concerns with the individual hospitals.'"