Ward G4 at West Suffolk Hospital has closed to new admissions after some patients showed symptoms of norovirus.
Around eight patients have shown symptoms of the highly contagious diarrhoea and vomiting virus.
Anyone visiting has been urged to take extra care to wash their hands with soap and water both on arrival and when leaving the ward, while anyone who has shown symptoms of the virus has been asked to stay away.
Rowan Procter, chief nurse at West Suffolk NHS Foundation Trust, said: “Norovirus is very infectious and every year there are cases in the community which transfer to the hospital. Because the virus has an incubation period of a few days, people are often unaware that they are carrying it until after they have passed it on.
“We would advise anyone who has had diarrhoea or vomiting to stay away from the hospital for at least 48 hours after they have recovered, even if they feel better.
“Otherwise they run the risk of unknowingly passing the highly contagious illness on to someone who is already sick.
“Anyone who visits the hospital should be vigilant and take care to clean their hands.
“If they are visiting the affected ward, they should use soap and water when they arrive and before they leave as the alcohol gel is not effective against this virus.”