TORONTO -- Staff at a Mississauga, Ont., nursing home made a series of errors that led to an 87-year-old resident being trapped in an elevator for more than 29 hours, an investigation has concluded.

Janette Smith, commissioner of health services for Peel Region, said staff failed to follow a number of protocols that lead to Rosalie Rowsell becoming trapped in the elevator at Malton Village Long Term Care Residence on Dec. 24.

"The investigation revealed that existing protocols were not followed by staff and that there were gaps in some policies and procedures," Smith wrote in the report, submitted to Peel Region council Thursday. "There was no wrongdoing on the part of the resident's family."

Rowsell was trapped in the out-of-service elevator shortly after she returned from a family outing on Dec. 23. She was last seen by a security guard around 8:30 p.m. after being signed in by her son.

She was discovered by Peel Regional Police as they swept through the nursing home looking for her in the wee hours on Christmas Day.

"We consider this occurrence as an extremely serious failure to maintain the level of care expected in a Region of Peel long-term care home," Smith wrote.

As a result of the investigation, staff is being re-trained and policies are being "enhanced."

Smith also said disciplinary action will be taken.

An external firm will be hired to review resident safety and security measures in all five long-term care homes the region operates, the report said.