York Health Services trust has been forced to postpone 200 non-urgent operations following an outbreak of infection. More than 20 patients and a dozen staff were affected by the Norwalk virus, which closed six wards at York District Hospital to new admissions. Trust deputy chief executive George Wood said the virus had proved 'difficult to clear'. Visitors affected by vomiting and diarrhoea were asked not to come to the hospital until they had been symptom free for 48 hours.