2011 Stepping Hill Hospital poisoning incident
The investigation was sparked by a nurse on a ward at the hospital, who noticed that several patients on the ward had unexpected low blood sugar levels. An investigation suggested that a number of saline ampoules and saline drips had been contaminated with insulin, and this was believed to have lowered the blood sugar levels in the patients. Three patients' deaths – two elderly males, George Keep, 84 and Arnold Lancaster, 71, and a female – Tracey Arden, 44 – were attributed to the alleged contamination,. However it was also reported that each of the patients also had underlying medical conditions that made them weaker. On 21 July 2011, it was confirmed that two more patients deaths were being linked to the investigation, bringing the death count to five. Greater Manchester Police (GMP) announced that the inquiry into how saline solutions had been contaminated with insulin would form the basis of a murder inquiry. During the investigation, 60 detectives were involved in determining how and when the saline solutions were contaminated. Meanwhile, a number of armed police guards were stationed at the hospital, and staff were made to work in pairs when administering medication to patients.
On 20 July 2011, GMP confirmed that they had arrested a 27 year old female nurse (originally mis-reported as being 26 years old) – Rebecca Jane Leighton, who worked at the hospital on ward A1 and A3 – in connection with the murder inquiry. The Nursing and Midwifery Council opened a fitness to practice investigation after the arrest of Leighton. It was revealed in the early hours of 22 July 2011, that detectives believed that a further 14 patients' saline may have been tampered with and that there may have been dozens more murders. On 22 July, Leighton appeared at Manchester City Magistrates' court. She was charged with three counts of criminal damage with intent to endanger life, three counts of criminal damage being reckless as to whether life was being endangered, and one charge of theft. She was remanded in custody to next appear at Manchester Crown Court on 1 August. Charges against Leighton were dropped on 2 September 2011. The Crown Prosecution Service said it was "no longer appropriate" to continue the case against her. Evidence that was expected to appear in support of the charges had not become available. Nazir Afzal, Chief Crown Prosecutor for the North West, said Miss Leighton had been charged on the basis there was “reasonable suspicion she had committed the offences and there were reasonable grounds for believing the continuing investigation would provide further evidence within a reasonable amount of time”.  She has since hired celebrity publicist Max Clifford (who has recently represented Shrien Dewani and Nicola Fisher) to help clear her name.
Insulin is often used as a treatment for diabetes, but for people without an insulin deficiency, an increase in insulin can be poisonous to the body. It was suspected that, due to the increased levels of insulin in the patients bloodstreams, they became ill and the three confirmed fatalities occurred. A number of other patients are also believed by police to have been poisoned in this way, though most did not suffer fatal consequences. Two further deaths in the A1 and A3 wards were added to the investigation on 21 July.
Insulin is also used on non-diabetic patients for the control of blood sugars in critical care settings. Stress hyperglycaemia is common in acute illness and treatment with insulin can reduse the risk of organ damage. Hypoglycaemia can occur in non-diabetics as a result of serious and critical illness, including heart, renal and liver failure as well as sepsis.
On 2 December 2011, it was reported that Rebecca Leighton had been dismissed from her job as a nurse at Stepping Hill Hospital. She had been suspended ever since the allegations were first made nearly five months earlier.
An appeal hearing, presided over by Stockport NHS Foundation Trust, against her sacking was held on Thursday 2 February 2012 but the appeal was dismissed. The Trust said it was unable to comment because of confidentiality issues and there was no response from Leighton's lawyers.
It was also revealed on that day that police were now investigating a total of 19 deaths at the hospital as possible victims of saline poisoning. By July 2012, the Greater Manchester Police stated that they were making good progress in the investigation, that twenty-two people were poisoned and that seven deaths occurred 
On 5 January 2012 it was revealed that a death that had taken place on 31 December 2011 was now being linked to the investigation. 46-year-old Victorino Chua, a nurse at the hospital, had been arrested amid claims that forms had been altered and a patient given extra medication. He was later also questioned on the earlier deaths. He was not been charged with any offence and was placed on police bail until an unconfirmed date in April, later extended to 10 September  On 10th. September 2012 Victorino Chua answered bail and was once again rebailed. Bail was extended to January 31. 2013. Bail was later extended two further times, to July 9 and November 29. 
On 29 March 2014 Victorino Chua was charged with the murders of Tracey Arden, Arnold Lancaster & Alfred Derek Weaver and 31 other offences including GBH and attempted poisoning. He was remanded in custody to appear at Manchester Magistrates' Court later.
- "BBC News – Police investigate three deaths at Stepping Hill Hospital". BBC. 15 July 2011. Archived from the original on 22 July 2011. Retrieved 23 July 2011.
- "Stepping Hill Hospital deaths: Suspect 'may be on site'". BBC News. 19 July 2011. Archived from the original on 22 July 2011. Retrieved 23 July 2011.
- "Stepping Hill Hospital: Nurse Rebecca Leighton Held For More Time After Five People Have Now Died | UK News | Sky". News.sky.com. Retrieved 23 July 2011.
- "Tributes to 5th patient to die in Stepping Hill saline sabotage probe as police ar e given more time to question nurse | Manchester Evening News". menmedia.co.uk. 11 July 2011. Retrieved 23 July 2011.
- "Rebecca Leighton quizzed by police as 5th patient dies of saline poisoning | Mail Online". Daily Mail (London). 19 July 2011. Archived from the original on 22 July 2011. Retrieved 23 July 2011.
- "BBC News – Stepping Hill Hospital: Nurse arrested in murder probe". BBC. 20 July 2011. Archived from the original on 21 July 2011. Retrieved 23 July 2011.
- "Nursing regulator opens fitness to practise proceedings in Stepping Hill case". Nursing and Midwifery Council. Retrieved 20 July 2011.
- Ford, Steve (20 July 2011). "Registered nurse arrested over Stepping Hill deaths named". Health Service Journal. Retrieved 20 July 2011.
- Tozer, James; Eccles, Louise (19 July 2011). "Rebecca Leighton held as police probe more Stepping Hill saline poison victims | Mail Online". Daily Mail (London). Archived from the original on 22 July 2011. Retrieved 23 July 2011.
- "Stepping Hill Hospital: Rebecca Leighton remanded in custody". BBC News. 23 July 2011. Archived from the original on 23 July 2011. Retrieved 23 July 2011.
- "Stepping Hill saline deaths: Nurse Rebecca Leighton charges dropped". BBC News. 2 September 2011. Retrieved 2 September 2011.
- "Rebecca Leighton: Nurse seeks help from Max Clifford". BBC News. 7 September 2011.
- "Nurse Rebecca Leighton dismissed from Stepping Hill". BBC News. 2 December 2011.
- "Stepping Hill nurse Rebecca Leighton loses sack appeal". BBC News. 3 February 2012.
- "Stepping Hill probe making good progress". Greater Manchester Police. July 2012. Retrieved 30 September 2012.
- "Stepping Hill Hospital saline inquiry: Nurse arrested". BBC News. 5 January 2012.
- Carter, Helen (8 January 2012). "Stepping Hill hospital nurse bailed". The Guardian (London).
- "Stepping Hill deaths: Nurse Victorino Chua charged with murder". BBC News. 29 March 2014.