Thousands of people in Britain have been sickened by the biggest outbreak of a winter vomiting virus in five years. Doctors estimate that hundreds of thousands of people may be affected by norovirus in the coming days. Dozens of hospital wards across the country have already been closed to try to stop the virus' spread. "General practitioners are seeing a huge number of cases of patients with the norovirus," said Steve Field, chairman of the Royal College of General Practitioners. Norovirus is the most common stomach bug in the United Kingdom, and its incidence typically spikes during the winter.