The number of swine flu cases in Scotland has risen six-fold in less than a week, making it the worst-hit part of the UK per head of population.

Thirty-one cases were confirmed north of the border yesterday. In the past four days, 100 people have fallen victim to the illness in Scotland, bringing the number of Scottish cases to 119. At the weekend, there were just 19.

A 44-year-old woman with the virus was admitted to the high-dependency unit at Royal Alexandra Hospital, Paisley, yesterday. She is said to have had an underlying health condition. A 23-month-old toddler in Lothian was also diagnosed and is being treated at home.

Three patients remain in intensive care at the Royal Alexandra Hospital. A 38-year-old woman at the hospital was said to be in a "critical" condition. A 45-year-old man and 23-year-old woman were described as "critical but stable" and "stable" respectively.

Scotland now accounts for a quarter of all cases of the virus in the UK, which has recorded 428 sufferers, including 23 new cases confirmed in England yesterday and one in Wales.

A bacterial expert said he didn't think there were "any reasons" why Scotland had been the hardest hit by H1N1.

"It is just the way you expect a virus to behave," said Hugh Pennington, from Aberdeen University. "It's not evenly distributed and it's more common in some parts of the country than others."

In England, Eton College will decide today whether to reopen on Sunday. It closed when six of its pupils were diagnosed with the virus.