A medical ward at Belford Hospital has been closed to new admissions due to an outbreak of diarrhoea and vomiting, believed to be caused by the winter vomiting bug.
Visitors are also being asked to stay away from Ward 1 at the Fort William hospital, where four patients have developed symptoms.
And NHS Highland has confirmed that one of the patients has tested positive for norovirus – also known as the winter vomiting bug.
A small number of staff on the ward have also been affected.
The virus, which causes diarrhoea, nausea and vomiting, spreads in the air where someone has had diarrhoea or vomited and is extremely infectious.
Consultant microbiologist for NHS Highland, Dr Jonty Mills, said: “Restricting visiting to the affected area helps hospital staff protect the health, privacy and dignity of our patients.
“We would also ask that people do not come to the hospital to visit if they have, or live with someone who has, had any vomiting or diarrhoea in the previous 48 hours.
“By doing this, we will be able to limit the spread as much as possible.
“Hospital staff will of course be very happy to talk to visitors on the phone so they can get updates on how their relatives are.”
Anyone who feels that visiting is essential must contact the ward by phone before coming to the hospital.
There is no specific treatment for a norovirus infection and it is not usually necessary to visit a doctor.
The best course of action is to stay at home, take paracetamol to relieve symptoms of any fever and to drink plenty of water to prevent dehydration.
Strict hand washing techniques should also be employed to reduce the spread of the virus.