A third patient has died from the C-diff infection at Edinburgh Royal Infirmary.
The infected patient was said to be very unwell from another illness for which they were receiving treatment.
There have been 14 cases of the Clostridium difficile infection which has prompted infection control experts to start an investigation.
Melanie Johnson, Executive Nurse Director, NHS Lothian, said: “I would like to express my sincere condolences to the family of the patient who died.
“Investigations are ongoing to establish if there is a link between the cases, but we don’t expect to have the results of forensic samples until January, which is a normal timescale for this infection.
“In the meantime, infection control measures have been enhanced and will remain in place. No new cases have been identified.
“If a cluster emerges, we always act as if cases are linked and implement action to prevent cross transmission.
“Our robust surveillance procedures meant that we were able to identify these cases quickly and take the appropriate action.”
Since the cluster was identified four patients have recovered and been discharged home.
The seven patients, who remain in hospital, are being cared for in isolation.
Infection prevention and control procedures have been reinforced to help protect them, other patients, staff and visitors. The five affected wards remain open.
Samples are currently being tested to establish if any of the identified cases are linked, although results are not expected until January.