A researcher from Oxford claims to have uncovered an underlying cause of the hospital superbug clostridium difficile.

Orde Levinson has written a paper concluding that contaminated urine samples could lead to the indiscriminate prescription of broad-spectrum antibiotics - one of the primary causes of C difficile.

Mr Levinson, whose firm JBOL is based at Folly Bridge, focused much of his research on Oxford's John Radcliffe Hospital, which he claimed was putting patients at risk by using non-sterile containers to collect urine.

He was also concerned the hospital's microbiology department was not fully accredited by Clinical Pathology Accreditation.

However, the hospital insisted patients had not been put at risk.

Oliver Francis, a spokesman for the Oxford Radcliffe Hospitals NHS Trust, confirmed the hospital stopped using sterile containers in March last year, because non-sterile devices were more cost-effective. He said the microbiology department was only "conditionally accredited".

But he dismissed the suggestion contaminated urine samples were a cause of C difficile. He said the 10 per cent rise in the number of the trust's patients contracting C difficile in 2006-7 should be seen in context of an overall 28 per cent drop between 2005 and 2007.

Mr Levinson said: "With a contaminated sample, the clinician is faced with a choice of whether to issue a broad-spectrum antibiotic or order a retest. The former is easier, because he doesn't have to recall the patient.

"He also wouldn't want to run the risk with pregnant women if the contamination is an early urinary tract infection, which has major implications for the unborn child and the mother, including kidney failure.

"First, the pathology department isn't accredited. Second, they use unsterile products in urine collection, which has been proven to cause contaminated samples.

"Why are they trying to save money by using unsterile products and put so much at risk?"

The trust said Mr Levinson was not drawing credible conclusions and urine samples were collected safely at the hospital.

Mr Francis added: "The treatment of patients is based on full clinical assessment and, if there is any uncertainty about the validity of a test, patients will be appropriately retested. Only those patients who need antibiotics receive them.

"The microbiology department was inspected against new, more stringent standards, which had recently been introduced."