CALGARY -- Five more patients and seven more health-care workers have tested positive for COVID-19 in connection with an outbreak at the Foothills Medical Centre in Calgary, officials reported Sunday.

Alberta Health Services also said two more units, a transitional medical unit and a short stay unit, have been added to the outbreak. It's not believed that the short stay unit is connected to the original outbreak. Three other units -- cardiac unit 82 and general medicine units 36 and 62 -- are under watch status.

There are 136 staff in isolation, with 25 health-care staff and 25 patients having tested positive for the disease so far.

There have been no new deaths since Saturday. Four people have died since the outbreak was first discovered earlier this month.

"I wouldn’t say staff are constantly on edge, I would say that people are definitely more vigilant now," said Dr. Rachel Grimminck with the hospital’s medical staff association.

"(There is) certainly worry about contracting the infection ourselves, but also bringing that home to our families."

Dr. Deena Hinshaw, Alberta's chief medical officer of health, says the province is investigating the cause of the outbreak, including reports of a visitor not wearing a mask inside the hospital and staff members working while possibly being symptomatic.

"We don’t want to be in a place where we need to look at restricting visitation again," said Grimminck.

If a unit has an outbreak watch, health officials monitor that area for any potential COVID-19 cases.

AHS says it is working to determine where the infection started.

"Multiple teams are working daily to determine where the infection may have started, how it was transmitted and who needs to be contacted and tested to limit exposure. This is standard procedure in our contact tracing that we implement with any outbreak."