A 52-year-old woman has been arrested over alleged ill-treatment of patients at Muckamore Abbey hospital.
The woman is the 16th person to be questioned by detectives working on the case.
She was detained on Tuesday morning by police in Antrim.
Earlier this month, the Public Prosecution Service decided to prosecute seven people over alleged ill-treatment of patients at the county Antrim Hospital.
The facility, which is at the centre of an ongoing major police operation, treats patients with severe learning difficulties and mental health problems.