More than 100,000 Britons have been downed by winter vomiting virus, its worst outbreak in the U.K. for five years. Health authorities anticipate a bigger number of victims in the coming days as the weather conditions worsen. The Health Protection Agency said the figure could double within the month.

The severe stomach bug, called norovirus, causes vomiting and diarrhea. To prevent the spread of the virus, victims have been advised to stay at home. The Royal College of General Practitioners said those affected by the norovirus must remain at home for two more days after they last experienced the bug's symptoms.

In 2002, two million Britons were infected with the virus. The fast spread of the virus is mainly caused by victims unknowingly catching the bug at school or the office and spreading it home. With schools scheduled to resume next week after the Christmas holidays, affected Britons were advised to remain home to prevent the bug from spreading faster among school children.

Norovirus is contagious, but not very dangerous. Frail seniors and very young children may be at risk of complications from dehydration and may require confinement in a medical facility. The symptoms usually appear within 12 to 48 hours after exposure and lasts for 12 to 60 hours. The virus is spread through contact with an infected person, contaminated food or water and contact with infected surfaces or objects.

Outbreaks of the norovirus are usually common in semi-closed places like schools, hospitals, nursing homes and cruise vessels.