Police confirm they are investigating two further deaths at Stepping Hill Hospital, where three other people have died as a result of suspected saline contamination.
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Assistant Chief Constable Ian Hopkins said that the deaths of two pensioners - 83-year-old Alfred Derek Weaver and an 84-year-old woman - are now being investigated.
Both patients had at some time been on hospital wards A1 and A3 which are at the centre of enquiries, where it is believed saline drips were "deliberately" tampered with.
The woman died on the 14 July but an initial post mortem failed to confirm the cause of her death. As a result the coroner passed the case to the police on Wednesday. A Home Office post mortem will now take place.
Greater Manchester Police also confirmed the death of Mr Weaver on Thursday morning after he suffered a "hypoglycaemic episode" on the 11 July.
Asst Chief Constable Hopkins said this death was of particular interest because the illness occurred "during a timeframe" they were studying.
"We have family liaison officers with both families and my thoughts are with them, as they are with the relatives of all affected by this incident," he said.
The police chief also stressed that as a result of working with a coroner, it was also very likely they will be asked to look into further deaths to see if they are related.
"In the main these are likely to be deaths of people who are elderly and/or ill, and we fully support the coroner's 'belt and braces' approach to ensuring future deaths that require further investigation are appropriately investigated and scrutinised.
"I cannot emphasise enough how complex an investigation this is, requiring detailed forensic and medical analysis, and want to take the opportunity to thank the hospital and staff for their ongoing help and support."
Hopkins reiterated that the police at this time could not confirm the cause of the five deaths until Home Office post mortem results are completed.
Asked by Channel 4 News if the police were concerned by any deaths before 7 July,Hopkins stated that the focus of the police investigation was "on the here and now".
But once they have brought to justice the person behind these "deliberate" acts, he said they would look at the deaths in the recent history of the hospital.
Police also confirmed they have 60 senior investigators on the case and that a 41-year-old male remains in a critical condition.
The announcement of the death comes after a nurse at the hospital, 27-year-old Rebecca Leighton, was arrested yesterday on suspicion of murder by police investigating three other deaths at the hospital.
Leighton was arrested at her home yesterday but has yet to be charged. It is expected police will extend the amount of time they have to question her. They say this does not mean there will not necessarily be further arrests.
Tracey Arden, 44, George Keep, 84, and Arnold Lancaster, 71, are thought to have died following the deliberate contamination of saline solution with insulin.
Another 14 patients were affected by the contamination, and one remains seriously ill.
Police believe that insulin was injected into saline containers, which were then used in intravenous drips in at least two wards in the hospital.
Dr Chris Burke, Chief Executive Stockport NHS Foundation Trust said on Wednesday: "We are aware that Greater Manchester Police have made an arrest this morning of a 27-year-old female.
"As the police are continuing with their inquiries, we are unable to provide any further details but it is important to stress that no charge has been made at this stage."
Security remains tight at the hospital, with ambulance admissions to accident and emergency being diverted to other hospitals and visiting has been restricted on one of the affected acute wards.