Other hospitals are being affected by the viral outbreak

The trust also says that four patients at the Western Infirmary are showing symptoms of the virus and have been isolated.

And one ward at the Royal Alexandra Hospital in Paisley has also been affected by an outbreak of sickness and diarrhoea.

Tests are being carried out to determine the cause of the outbreak which was discovered on Monday.

The Victoria Infirmary in Glasgow, where more than 250 patients and staff have fallen ill, was the first to close its doors.

Health chiefs had hoped to resume operations and admit new patients on Tuesday, but that plan has now been delayed for at least another few days.

Patients affected

Glasgow's Southern General has been taking additional patients because of the viral outbreak at the Victoria.

The bug has also struck a total of 56 people in the Forth Valley area, with two wards shut at Stirling Royal Infirmary and one closed at Falkirk Royal Infirmary.

It has also hit Borders General Hospital in Melrose, where more than a dozen patients and staff have been affected.

Patients were hit at Borders General Hospital

"The outbreak has been contained to two wards and the rest of the hospital is functioning fine," said a hospital spokesman.

Nine patients and four members of staff are recovering after being affected at Ashludie Hospital in Monifieth, Tayside.

Medical experts have stressed that the viral outbreak is not related to hygiene and is an airborne illness which is highly contagious.

The "winter vomiting" bug is very common and affects more than 50,000 people in Scotland each year.

I think it is time to take a tougher approach to hospital cleanliness

Nichola Sturgeon, SNP

However, the outbreak at the Victoria Infirmary is said to be unusually large.

The bug has also struck down pupils at Forthill Primary School in Dundee, where 70 children were still off school on Tuesday.

Health economist, Dr Andrew Walker, said the cost of tackling hospital acquired infections (HAIs) was growing.

"I think it is probably about �135m a year to treat the infections that are acquired in hospital," he said.

"That will roughly be on a par with treating strokes."

The Scottish National Party said it wanted the Health and Safety Executive to enforce hygiene standards in Scottish hospitals.

Nichola Sturgeon, SNP health spokeswoman said: "I think it is time to take a tougher approach to hospital cleanliness and hospital acquired infections.

"More people die every year from infections that they pick up in hospital than they do in road accidents.

"That is a stark statistic."