On its website, it says the person was a non-resident care staff member.
The region says that no one else connected to the home has tested positive up until Monday.
The region says all residents and staff members who may have come in contact with the person or has shown symptoms have been isolated and tested.
Staff will not be allowed to return to the home unless they have the approval of Waterloo Public Health.
The home is maintaining staff levels through redeployment and all non-essential visits to Sunnyside Home have been suspended.
Waterloo Region runs the long-term care home which houses 263 people in the Stanley Park area of Kitchener.