A Stillwater prison inmate who tested positive for COVID-19 died Sunday, becoming the third Minnesota inmate to die after contracting the virus.

The 61-year-old man, whose name was not released by the Minnesota Department of Corrections, died Sunday morning at the prison. His death came a day after he'd been taken to a hospital, examined and discharged, according to a new release from the department. The man had "an extensive medical history" and his official cause of death will be determined after an autopsy by the Ramsey County Medical Examiner.

In a statement, Department of Corrections Commissioner Paul Schnell expressed his sympathies to the man's family.

"Since the beginning of this pandemic we've worked to take all reasonable steps to minimize the introduction and spread of COVID-19 in the state's correctional facilities for the well-being of those we serve and our staff," he said.

The Stillwater prison did not report a COVID-19 case until late September, but since then it has been the site of an ongoing outbreak. Of the 1,278 inmates there, more than 750 have tested positive for the virus, along with more than 150 staff members. State officials said most of the inmates and staff who have tested positive have shown no symptoms.

The Department of Corrections said it is investigating why the virus has spread more quickly at Stillwater than at other facilities: "We continue to investigate whether facility age, design, and infrastructure may influence the spread of COVID-19 and other viral infections, such as the flu."