Four COVID-19 cases are now reported in staff at a prison in Kingston, Ont., where 80 inmates tested positive.
Correctional Service Canada says the employees work at Joyceville Institution, where a major outbreak was declared Thursday.
The outbreak has been linked to eight cases at two other prisons in Ontario.
The federal agency has suspended all in-person visits at its facilities in the province.
Prison authorities say all employees are actively screened for COVID-19 before entering the institutions.
They say all staff and inmates have been offered testing.
This story was produced with the financial assistance of the Facebook and Canadian Press News Fellowship.
Sign up for the Coronavirus Update newsletter to read the day’s essential coronavirus news, features and explainers written by Globe reporters and editors.