An assisted living facility in Mississippi must face trial on a nurse’s claim that it failed to take action when a mentally ill patient repeatedly sexually harassed her and other staff.

The June 29 ruling addresses the challenging issue of when an employer may be held liable to a worker for harassment by a nonemployee whose mental capacities are diminished. While the “unique nature” of health care and certain other workplaces is an important factor in deciding whether unlawful harassment has occurred, employers aren’t immune from potential liability in all such situations, the U.S. Court of Appeals for the Fifth...