Estimating the risk of vCJD transmission by blood and surgery

A problem presented at the Canadian MMSG Toronto 2009.

Presented by:
Dr. Mustafa Al-Zoughool (McLaughlin Center for Population Health Risk Assessment, University of Ottawa)
Dr. Tamer Oraby (McLaughlin Center for Population Health Risk Assessment, University of Ottawa)
M Al-Zoughool, V Anvari, M Atapour, L Bourouiba, L Caudillo Mata, S Collinson, V Duvvuri, H Guo, A Johnson, N Madras, P Miasnikof, T Oraby, L Ramírez Ramírez, I Sanchez-Bravo

Problem Description

The new variant Creutzfeldt Jackob Disease (vCJD) is the human form of the mad cow disease or the Bovine Spongiform Encephalopathy (BSE), caused by non-conventional infective proteins called prions. Prions have been shown to be resilient to traditional cleaning measures. Secondary transmission of vCJD is controlled through a number of measures.

Mitigation of surgical transmission has been mostly handled through the limitation of reuse of surgical instruments especially through high-risk procedures. Risk of vCJD in the blood system is basically controlled by means of donor deferral policies, treatment of blood products (leukodepletion, for example) and the use of a detailed tracking system in the case of suspected vCJD infection.

Our Proposed model would address the issue of the risk of secondary transmission of vCJD by blood transfusion and surgery. A total of 16 cases of mad cow disease have been detected in Canadian cattle and it is possible that some infected cattle have been slaughtered for human consumption. The model will include a number of parameters such as transmissions probabilities, re-use rates and population sizes.

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Study Group Report

We have presented two different simple models for vCJD transmission by blood transfusion. Both models indicate that transfusions alone are unlikely to cause more than a few infections, unless the number of primary cases increases.

To improve our models, future work should pursue data collection, empirical estimation of the model parameters, and examination of the underlying assumptions of our frameworks. Further improvements could also include examining susceptibility to vCJD infection by age group and iatrogenic infections introduced through surgical instruments. Regarding the latter, it may be worthwhile to conduct experiments to quantify the transmission of prions from an infected surgical instrument after repeated sterilization procedures.

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