Nearly 40 patients and six staff at Dumfries and Galloway Royal Infirmary (DGRI) have been struck by a vomiting bug thought to be the norovirus.
Three wards have been closed to new admissions and patient transfers after the first case was reported on Saturday.
To date 38 patients and six staff have been affected with 20 still showing symptoms.
NHS Dumfries and Galloway said its outbreak control team had been meeting daily to monitor the situation.
A spokesman said: "NHS Dumfries and Galloway has put in place robust infection control measures during the outbreak at DGRI and our outbreak control team is monitoring the situation closely.
"We apologise for the inconvenience these necessary precautions are causing towards visiting but with the cooperation of the public and their assistance in adhering to hand hygiene measures in place, we remain confident that we can restrict the spread of infection as far as possible.
"Any family member or visitor who may have concerns about whether it is appropriate to visit a loved one should contact the ward concerned in advance and discuss their particular circumstances with a senior member of the nursing team."
"The norovirus - which is yet to be formally confirmed - is very common in the community around this time and such outbreaks can reflect what has been happening in the community at large.
"We urge all the public to follow good hand washing and hygiene precautions in their own areas."
The norovirus has led to more than than 1,000 ward closures in Scottish hospitals over the past three years.
The total was highlighted by Liberal Democrat health spokeswoman Alison McInnes last month.
A ward at Ninewells Hospital in Dundee also recently closed to new admissions after several cases of the Norovirus but was reopened on Tuesday.
- Winter vomiting bug forces closure of two hospital wards to new patients
- More than 1000 wards closed by norovirus in three years