Four hospital wards have been affected by an outbreak of sickness and diarrhoea.
Nine patients are currently being treated for the highly infectious bug at Worthing Hospital.
Two wards have been temporarily closed to new admissions while bays in two other wards have also been restricted.
Hospital managers are assessing the situation daily and are hoping to reopen the wards as soon as they have been cleaned and all patients are symptom free.
Cathy Stone, director of nursing and patient safety, said: “Whenever there are illnesses circulating in the community, we would ask everyone to help us keep infections out of our hospitals and away from patients who may be particularly vulnerable.
“We do all that we can to stop a single case in our wards becoming more widespread, but the best way to keep people safe is to try to stop such illnesses being brought into hospital in the first place.
“It is crucial that people don’t come into hospital to visit friends or relatives if they have suffered from sickness or diarrhoea within the last 48 hours – I would ask that people please remember that, to help keep others safe and well.”
Visitors are also asked to use the hand cleansers when visiting.