Resident were evacuated from a wing at St. Mary's Villa Boxing Day because of a carbon monoxide leak. Three seniors later died. (City of Humboldt)

A third person from the Humboldt, Sask., nursing home where residents were exposed to carbon monoxide due to a faulty furnace has died.

The woman, a 98-year-old, had been in "declining health" since Dec. 26 when a wing of the St. Mary's Villa was evacuated, the Saskatoon Health Region announced Thursday.

A total of 31 people, including 24 residents, five staff and two visiting relatives of residents were taken to hospital for treatment.

The woman died Wednesday and officials said carbon monoxide "may be one contributing factor." Her name was not released.

Officials said the case had been referred to the provincial coroner's office.

Two other residents of the home died following the gas leak, an 89-year-old man and a 94-year-old woman.