Norovirus bug affects Sheffield's Northern General Hospital
Sheffield's Northern General Hospital has closed three wards to new admissions after an outbreak of the norovirus winter vomiting bug.
NHS Sheffield Teaching Hospitals has asked people who might be infected not to visit patients for 72 hours.
The contagious virus causes vomiting, diarrhoea and fevers.
Deputy Chief Nurse Chris Morley said he expected it to take "two or three days" for the affected wards to be cleared of the virus.
Mr Morley added: "Unfortunately in the period shortly before symptoms become apparent, people are infectious, so you can actually be spreading the infection without even realising that you are affected.
"It's important that anyone who's been in contact with someone with these symptoms keeps away from hospitals and older people."