The Norwalk virus is highly contagious

The norovirus, or Norwalk-like virus, affects up to one million people in the UK each year.

The first case was diagnosed last Thursday, and about 40 patients and 30 staff have been affected.

Dr Jim McFarland, Medical Director with the Ulster Community and Hospitals Trust, said they were hopeful of being able to contain the outbreak.

Victims suffer vomiting and diarrhoea for about 48 hours before the infection passes, with those affected remaining infectious for a further 48 hours.

Dr McFarland said measures have been taken to stop the virus spreading, with a number of infection controls being put in place.

He said that it was a virus that was present in the community and was being brought into hospitals.

"This is an increasingly common virus which probably emerged about two or three years ago it has been seen on cruise ships as well as in hospitals and this is something I'm rather afraid that hospitals are prone to today," he said.

He that he believed good hygiene was the key to beating the outbreak, and not just in hospitals but also the wider community.