KITCHENER -- Grand River Hospital has declared a retroactive COVID-19 outbreak on 5 Centre, a part of its medicine program.

The hospital said on Monday it identified cases related to the outbreak through contact tracing after four staff and two patients tested positive.

The staff cases were first found on Nov. 25, but the hospital couldn't find an obvious link in the hospital until some patients were tested, a spokesperson for the hospital said.

Infection prevention control staff are working around the clock in an effort to stop any further spread.

"We are focusing on implementing additional precautions to contain the spread and protect the health and wellness of both our patients and staff," said Bonnie Camm, the executive vice president of clinical services at the hospital, in a news release.

The hospital has decided to close admissions to the unit temporarily while increasing cleaning of high-touch surfaces. Officials have also temporarily suspended in-person care partner visits, working instead to improve virtual and phone visits with family.

It'll be the second active COVID-19 outbreak at Grand River Hospital. The other was declared in the Medicine Unit 5S, the region's online dashboard shows.

Over the weekend, St. Mary's General Hospital also declared a COVID-19 outbreak in its chest unit, while an outbreak was declared at Cambridge Memorial Hospital's Level 4 Medicine B Unit on Nov. 13.

"With the outbreaks now at three hospitals, this will reduce our capacity to provide our services more generally," said Lee Fairclough, president of St. Mary's General Hospital.

Fairclough said the outbreak is putting a strain on staff and services in the health care system.

"We will do everything that we can to ensure the safety of the patients on that unit and the safety of our staff," she said.

A total of six staff members have now tested positive for COVID-19 in an outbreak at Stratford General Hospital. The outbreak was declared on Dec. 3 after two staff members tested positive for the disease. Officials with Huron Perth Healthcare Alliance said no patients have acquired the disease while in the hospital.

There were a total of 23 active outbreaks in Waterloo Region as of Monday morning, the region's dashboard showed.

Public health officials have reported nearly 4,000 cases of COVID-19 in the region since the pandemic began.