A fourth ward at North Devon District Hospital has been closed to new admissions after patients have shown symptoms of vomiting and diarrhoea.
King George V ward has been temporarily shut, although the hospital has said no cases of Norovirus have been confirmed there since November 2012.
Staples ward is also not accepting new admissions after it was closed last week along with Glossop and part of Capener ward, although these are now open as usual.
Jim Bray, a spokesman at NDDH, said: "Every time a patient shows symptoms of diarrhoea and/or vomiting, extra infection control precautions are put in place in case they have Norovirus. These include temporarily closing a ward, or part of a ward, to new admissions.
"A few patients have shown symptoms of diarrhoea and/or vomiting recently. Staples Ward and King George V Ward are temporarily closed to admissions for this reason.
"A six-bedded bay on Capener Ward was temporarily closed to admissions for a spell last week. No Norovirus infection was identified and the ward is now open as usual."
The Trust asks hospital visitors to help the situation by staying away if they have experienced diarrhoea and/or vomiting in the previous 48 hours, or been in contact with anyone who has had similar symptoms.