The Children’s Hospital of Eastern Ontario is watching who visits its pediatric intensive care unit after a viral outbreak.

Hospital spokesperson Ann Fuller said three children contracted respiratory syncytial virus, or RSV, between Jan. 5 and 8.

The common disease can cause severe illness such as pneumonia in very young children, according to the Canadian Lung Association.

Fuller said CHEO is working to make sure the virus doesn’t spread.

“We did a really thorough cleaning of all the rooms, the equipment and all the common areas that are used on that one unit,” she said.

“We reduced the movement of staff on that unit and volunteers are not permitted on that unit, and we're also restricting visitors on that unit — again just as a precaution — only the parents or guardians can visit the kids on that unit.”

The Canadian Lung Association said most children under the age of three will contract RSV and it’s usually a mild illness that will go away on its own.