Government inspectors are to probe patient safety at Stepping Hill Hospital following the deliberate contamination of medicine.
The Care Quality Commission will investigate how staff handle and store medication.
Detectives believe a rogue worker injected saline with insulin, poisoning 21 patients – six have died after their saline drips were contaminated.
If the CQC raises concerns, the hospital could get a compliance notice – and ultimately a fine or have wards closed if any recommendations aren’t then met.
Hospital bosses say they have since been through safety procedures ‘with a fine tooth comb’ and insist they now exceed requirements.
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A CQC spokesman said: "The CQC has been liaising directly with NHS North West and continues to work closely with both the NHS North West and Stockport NHS Foundation Trust to monitor actions being taken to ensure patient safety in this area.
"The CQC will be returning to Stepping Hill in the near future to conduct a further unannounced inspection."
Hospital bosses say the incident could have happened anywhere and was not the result of poor safety standards.
Director of nursing Judith Morris said a raft of strict new safeguards – including keeping saline under lock and key – will probably be permanent and become standard practice nationwide. She added: "It has led us to question all the things we have done not only as a result of the incident but before."
A hospital spokesman said: "We have introduced a number of new security measures since the incident which are above and beyond standard NHS practice. We have liaised closely with our NHS partners about the new security measures and will continue to work with them."
The deaths of Tracey Arden, 44, Arnold Lancaster, 71, Derek Weaver, 83, former M.E.N. news editor Bill Dickson, 82, Linda McDonagh, 60, and John ‘Jack’ Beeley, 73, are under investigation.
Mr Dickson, Mrs McDonagh and Mr Beeley all died between New Year’s Eve and January 20 – several months after it is believed they were poisoned.
They were among a number of patients who suffered a ‘hypoglycaemic episode’ after saline solution, kept in a storeroom between wards A1 and A3, was contaminated. They were all being treated on acute wards for seriously ill patients. Tests are continuing to find the precise cause of death, and whether the poisoning contributed to their deaths.