Day patients, family and friends are being asked to stay away from the Knowle Hill care home on High Street in Beighton.
Councillor Chris Peace, cabinet member for Health and Social Care at Sheffield Council, today confirmed there was currently one person from the home known to be unwell.
She said: 'The staff are working hard to ensure that all guidelines from Health Protection England and the CCG continue to be followed to ensure the virus does not spread further.
'Family and friends wanting to visit the home will be supported to do so as soon as is practical.'
Knowle Hill opened at its current site last year after moving from Halfway and specialises in care for older people with dementia.
At its last inspection in September, it was given a '˜requires improvement' rating by the Quality Care Commission.