Twelve employees from a Walmart in South Edmonton have tested positive for COVID-19 as part of an outbreak, and Alberta’s top doctor said she doesn’t yet know how it started.

A Walmart spokesperson confirmed other staff at the South Park Walmart Supercentre on Calgary Trail who were in close contact with the dozen who are sick are also self-isolating.

“We are keeping the associates in our thoughts and wish them a speedy recovery,” the company said.

“The store is currently closed and will reopen in the coming days when we can offer the very best experience for our customers. We will be conducting a deep cleaning.”

Chief medical officer of health Dr. Deena Hinshaw said the origin of the outbreak has not been identified yet.

“It’s not clear if they were exposed at work or a common exposure outside of the workplace.”

Walmart said it was working to ensure the wellbeing of staff and customers with increased cleaning protocols, temperature checks for employees and store limits.

The province reported more than 400 positive cases over the weekend, including another new outbreak at an Ethiopian Orthodox church in Calgary. Fifty-seven cases are linked to that outbreak.

As of Monday, there were still 1,370 Albertans sick with the disease. The Edmonton medical zone accounts for 551 of active cases, but was removed from Alberta’s watch list last week.

A southwest 7-Eleven and Tim Hortons location also closed Monday after an employee was confirmed to have COVID-19.