The situation is being managed by NHS Borders Infection Prevention and Control Team with support from frontline colleagues.
Visitors to Ward 4 are strongly discouraged, and the general advice to members of the public is to stay away from any hospital ward if you or anyone in your family has experienced symptoms of diarrhoea and/or vomiting in the past 48 hours.
Dr Ed James, consultant microbiologist, said: “Norovirus is one of the most common causes of diarrhoea and vomiting illness.
“It is very infectious and spreads quickly between people. This is why outbreaks happen in hospitals where a number of people are sharing facilities. However it doesn’t just occur in hospitals, and can start abruptly and spread quickly through communities.
“It is vital to protect yourselves and your loved ones from catching this unpleasant virus. Patients, visitors and staff can help minimise the spread by complying with instructions given by staff and paying attention to the signs at the entrances to the hospital and wards.”