Visitors to the Norfolk and Norwich University Hospital (NNUH) are being as to avoid wards affected by Norovirus.
The hospital said it was not accepting new admissions onto one ward due to patients being infected with the stomach bug.
And while it has not introduced a blanket ban on visiting, it has asked people not to visit unless absolutely necessary.
Dr Ngozi Elumogo, director of infection prevention and control at NNUH, said: 'It is that time of year where we see Norovirus circulating in the community and our advice is to wash your hands as a matter of routine with hot, soapy water.
'Hand sanitisers and alcohol gel will work against some bacteria and flu viruses but they will not protect you against Norovirus.
A hospital spokesman said it was important for people not to visit if they have a stomach bug, or have been in contact with someone who has over the past three days.
People should also avoid bringing in children under 12 years.
Dr Elumogo added: 'During Norovirus outbreaks we ask people to wash their hands instead of using hand sanitiser.
'To keep Norovirus out of hospitals, it is important that people do not visit patients if they have been ill with a stomach bug in the previous 3 days or in close contact with someone who has had sickness or diarrhoea.'
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