An elderly patient has died after an outbreak of Clostridium Difficile at Perth Royal Infirmary.
Three other elderly patients in the hospital's Tay ward have now also contracted C Diff - two still have mild symptoms of the bug and the other is recovering.
NHS Tayside said C Diff was a factor in the death but was not the main cause.
The patient tested positive for the infection on February 12 and was immediately placed in isolation.
An infection-control team is dealing with the outbreak and the affected ward is closed to new admissions.
Consultant microbiologist Dr Gillian Orange said the ward was closed to new patients as a precaution and that "all appropriate procedures" have been put in place to deal with the infection.
The hospital is contacting every patient who was discharged from Tay ward since Friday March 26.
Labour health spokeswoman Jackie Baillie said the outbreak should be investigated to find out how it happened.
She said hospital-acquired infections such as C Diff are a "real threat to patients", and added: "Our thoughts are with the families affected by this outbreak."
Ms Baillie said: "There needs to be an investigation of how this outbreak occurred, when the first case was identified and whether all appropriate steps were taken to prevent the spread of C Diff to other patients in Perth Royal Infirmary."
In October last year seven elderly patients in a ward at Ninewells Hospital in Dundee caught C Diff - two people died as a result and the bug contributed to the deaths of three others.Thompsons Personal Injury Solicitors is representing the families at the C Diff public inquiry which is hearing evidence into the deaths of 18 patients at the Vale of Leven hospital and the Ninewell deaths.