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Friday, 30 June, 2000, 01:07 GMT 02:07 UK
Blood link to CJD 'not ruled out'
Blood donation
Studies suggest there is low risk of contracting CJD by blood transfusion
It is still too early to rule out a link between the human form of "mad cow disease" and blood transfusions, say doctors.

Researchers at the University of Ottawa have suggested that while there is no evidence to support such a link, it is still impossible to dismiss it.

The researchers examined five studies into Creutzfeldt-Jakob disease (CJD), a degenerative brain disease that generally affects elderly people.

Incidence of the disease is quite low, affecting one in every million people.

Low risk

Each of the studies reported varying but low levels of risk of contracting the disease as a result of a blood transfusion.

And they all suggested that transfusions may, in fact, protect against developing CJD.

However, the Canadian researchers have suggested that the methodology of some of the studies may have resulted in "flawed" results.

The studies compared the proportion of CJD victims who had received transfusions with those from control groups.

However, three of the studies used medical patients in their control groups. The Canadian researchers said: "Presumably, these individuals would be at higher risk than the average population of having received a blood transfusion."

They suggested that because they used medical patients, the conclusions of these studies would be "biased" towards indicating a low risk of contracting CJD from a transfusion.

They added that such "limitations" meant that a link between the two could not be ruled out.

Dr Kumanan Wilson, assistant professor in the division of general medicine at the University of Ottawa and one of the authors of the study, said future studies could overcome these limitations.

He told BBC News Online: "They can be overcome by using general population controls instead of hospital patients."



It is very difficult to have conclusive evidence, because it can take 20 years for classical CJD to develop

Dr Kumanan Wilson, University of Ottawa

He added that the fact that it can take up to 20 years before CJD develops, research in this area will always be difficult.

"This study in culmination with other evidence has not demonstrated any link. However, we cannot absolutely rule it out.

"It is very difficult to have conclusive evidence, because it can take 20 years for classical CJD to develop."

Lessons

The researchers concluded that their findings had lessons for any research examining the link between variant CJD and transfusions.

Variant CJD (vCJD) is contracted by eating BSE-infected material, such as meat from cows.

"Despite the methodological advantages of case control studies in studying rare disease with long latency periods, potential exists for significant levels of bias that can produce apparently spurious results.

"It is important to recognise these limitations when attempting to address the question of infectivity of variant Creutzfeldt-Jakob disease in blood transfusion."

The study is published in the latest issue of the British Medical Journal.

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See also:

21 Dec 99 | Health
CJD: What is the risk?
24 Feb 00 | Health
Drugs 'slow mad cow disease'
19 Jan 00 | Health
CJD 'will not be an epidemic'
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