Assessing the risk of vCJD transmission via surgery: models for uncertainty and complexity

Variant Creutzfeldt-Jakob disease (vCJD) is a fatal degenerative brain disease, which probably passed into humans from cattle infected with bovine spongiform encephalopathy (BSE) or 'mad cow disease'. Whatever its origins, the question arises of whether vCJD could be spread from person to person. Any such risk is very difficult to quantify, not least because the number of people already infected is unknown. This paper reflects on a study assessing the risk of transmission via instruments used in hospital surgery. The study underpinned a number of policy initiatives, including a pound200 m programme to improve instrument decontamination. The methodology had to meet two major challenges. That of dealing with very large and multiple uncertainties was initially addressed using simple spreadsheet-based models to generate alternative scenarios. The complexity in the possible dynamics of vCJD within the population was then tackled. This paper outlines the models built and their use in eliciting expert judgement and informing risk management policy.