An inquiry is being sought into an outbreak of the deadly bug Clostridium difficile which has been linked to seven patient deaths in one hospital.
Prince Charles Hospital in Merthyr Tydfil, South Wales, had 33 cases of the bug on their wards in April alone.
The Welsh Assembly shadow health minister Jonathan Morgan AM has now called upon the Auditor General to intervene in the matter. In a letter to Jeremy Colman, Mr Morgan asked him to conduct an independent review into cases of C diff at the hospital.
In the letter, Mr Morgan said: "I understand that in April this year 33 patients at the hospital were found with C diff, seven of whom died with it being mentioned on the death certificate. Apparently the figure has risen considerably from 15 last year.
"Whilst I appreciate that your office has already done a considerable amount of work on the challenges faced by our hospitals in combating the spread of infection (and the Audit Committee report) I was wondering if you could examine the specific issues at Merthyr.
"There may be problems that are more acute at Prince Charles Hospital which could explain why there has been this increase.
"As you are aware there is a significant public interest in this matter and I firmly believe that in order for confidence to be rebuilt we need an independent view of the problem. As Auditor General for Wales you are in a unique position to undertake this work and advise us of the appropriate action required."
Mr Morgan later commented: "I am extremely concerned at recent reports into hygiene standards in Welsh hospitals. While I welcome efforts to improve cleanliness levels it is clear much work still needs to be done.
"Patients deserve to be treated in clean hospitals and in an environment where their health is not threatened by illnesses contracted when they are being cared for. The Assembly Government says it is committed to tackling the spread of hospital acquired infections such as MRSA and C diff. We will hold them to that.
"Ministers must agree to publish infection rates per hospital for all those who contract conditions such as MRSA and C diff, not just for specific age groups. The Assembly Government must also back this up with appropriate investment to ensure hospitals and wards are kept clean."