A mentally diminished teenage patient at the Minnesota Security Hospital grabbed a staff member by the hair and bashed her head against a brick wall, then kicked her in the head repeatedly, a labor union official said Tuesday.

The assault occurred Monday night in the courtyard of the security hospital, located in St. Peter and run by the state Department of Human Services (DHS).

The staff member was hospitalized overnight and released after suffering what the DHS described as “serious” injuries.

The patient, a 16-year-old with “low cognitive abilities,” is now isolated from other patients and under constant supervision by two staffers, said Jennifer Munt, an official with the American Federation of State, County and Municipal Employees (AFSCME), the union representing the mental hospital’s staff members.

Carol Olson, the DHS’s forensic treatment services executive director, released a statement about the incident:

“A patient at the Minnesota Security Hospital assaulted a staff member, resulting in serious injury to the staff member. Last night, we called local law enforcement and are working with them on appropriate action. We remain committed to a safe and secure treatment environment for employees as well as patients and will carefully review this incident to determine how situations like this can be prevented in the future.”

Last year, the security hospital hired nearly 60 more staff to improve security and treatment following repeated incidents of patient maltreatment and abuse, as well as the slaying of a patient in January 2014.

The DHS also had to retrain much of the staff to engage with patients more directly and rely less on restraints and seclusion.

“If they could have used restraints and seclusion, this could have been prevented,” said another AFSCME official, Matt Stenger, vice president with Local 404 and a staffer with St. Peter’s sex offender program. “These things are occurring more and more frequently.”

Munt said Monday night’s incident began when the teenager “started getting aggressive with other patients” over a period of about two hours. Three security counselors took the teen into the courtyard “in hopes of calming him down so he wouldn’t hurt other patients.”

The patient grabbed one of the counselors “by her hair and bashed her head repeatedly into a brick wall,” Munt said. “She started convulsing and fell to the ground.”

He continued the assault, Munt added, kicking the counselor in the head many times. The other two counselors pulled the patient off their colleague.

“It all happened very quickly,” Munt said.

Hospital personnel called local law enforcement, but it could not accept the teen because the Nicollet County jail lacks a lockup for juveniles, Munt said.

The Sheriff’s Office in Carver County was contacted, but officials there said they could not take the patient because of his low cognitive abilities, Munt added.

“The patient is still at St. Peter, with two staff assigned to him” at all times, she said.

Stenger said the teenager “is not restrained. … He’s out watching TV with [other patients]. He could act out again at any time.”

The security hospital is only licensed to treat adults. However, according to a statement Tuesday from the DHS, “there are, at times, circumstances” in which variances can be requested and granted.