AN outbreak of the winter vomiting bug could have affected thousands of people in Bolton.

But so far this winter, the Royal Bolton Hospital has not been badly affected.

Norovirus, which is a highly infectious disease and is very difficult to monitor, spreads rapidly in hospitals, schools and other environments where there are a large number of people in close proximity.

Across the UK, there has been a 72 per cent increase in cases compared to last year — with 100,000 people thought to be struck down by the bug over Christmas.

The rise was partially attributed to an early outbreak of the disease, which closed dozens of hospital wards across the country.

It is difficult to calculate accurate figures for norovirus, as only a handful of those who have the bug will be tested for it.

The Health Protection Agency (HPA) has said for every reported case, an estimated 288 were not flagged up, meaning about 1.12 million people could have contracted the illness this season in the UK.

Using the HPA’s calculations, this means 6,048 people had the bug in Bolton between March 2011 and November 2012, and 1,152 people were infected between March 2012 and November 2012.

Graham Munslow, health protection specialist for NHS Bolton, said the calculations could be “misleading” and the majority of people with norovirus will not be tested. A number of Bolton schools were affected by the vomiting bug and the infection spread widely into the community.

Although the Royal Bolton Hospital was affected by norovirus, with a number of wards and bays closed to new admissions over the Christmas period, and strict restrictions including children banned from visiting and adults limited to two per bed, there was not a major outbreak.

Accurate figures of norovirus infections at the hospital are not available as if one patient on a ward where patients are affected by vomiting and diarrhoea tests positive, the rest are not tested for the bug, but are included in the quarantine.

Heather Edwards, head of communications at Bolton NHS Foundation Trust, said: “Although there has been a lot of diarrhoea and vomiting in the community, the hospital up until now, has not been as badly affected as in previous years.

“This has been helped by raising public awareness and strict adherence to infection control.

“It is usually later in the season that we see most cases of diarrhoea and vomiting-type symptoms.”

Norovirus symptoms include sudden vomiting, diarrhoea, or both, a temperature, headache and stomach cramps.

People are advised to stay away from schools, hospitals and nursing homes until 48 hours after symptoms have passed.