A Blackpool Victoria Hospital nurse has been arrested on suspicion of poisoning patients.
She was arrested on suspicion of administering poison or noxious fluids with the intent to injure, as well as ill treatment and wilful neglect.
She has been bailed until December 6 and has been suspended by the hospital.
Police began investigating allegations of mistreatment and neglect by a medic at the hospital after they were contacted by Blackpool Teaching Hospitals NHS Foundation Trust on November 8.
The hospital trust said it became concerned for the welfare of patients after allegations relating to the alleged mistreatment and neglect of patients on the stroke unit earlier this month.
Det Chief Insp Jill Johnston, of Lancashire Police said: “This arrest is part of an on-going investigation into allegations of mistreatment of patients by a healthcare professional at Blackpool Victoria Hospital.
“The inquiry is complicated and we have a team of specialist detectives working on this case who are also offering support to those families who have had loved ones identified as potentially being involved.
“Our priority and the priority of Blackpool Teaching Hospitals NHS Foundation Trust is to ensure the safety of patients. We are working closely with the Trust as part of the investigation.
Enquiries are on-going."
A team of detectives are at the early stages of their investigation and are working closely with Blackpool Teaching Hospitals NHS Foundation Trust.
Wendy Swift, Chief Executive of Blackpool Teaching Hospitals NHS Foundation Trust, said: “We can confirm a healthcare professional has been suspended in line with Trust policy following allegations of mistreatment against patients on the Stroke Unit
“We take all allegations of this type extremely seriously and when the concerns were raised we immediately contacted the police.
“The Trust is working with the police and co-operating fully with their investigation.
“We would like to reassure all our patients that all necessary actions are being taken. The hospital remains a safe and caring environment for patients and the provision of services will continue as usual.’’
Blackpool Victoria Hospital, in Whinney Heys Road, is the main hospital for Blackpool and the Fylde Coast and the leading hospital for heart surgery in the region.
If you wish to report any concerns or raise any issues to hospital staff, please contact 01253 952270 between 8.30am and 5pm.
Anyone with information can contact police on 101 quoting log reference 0553 of November 14.
Alternatively, if you have any information which could assist the police investigation, please go to: https://mipp.police.uk