The Queniborough CJD cluster
The reported link between five cases of variant Creuzfeldt-Jakob disease and contaminated meat in a UK village is based on nothing - except bad science.
Five cases of variant Creuzfeldt-Jakob disease (CJD) in the North Leicestershire village of Queniborough have been attributed to local butchers relying on small abattoirs supplied by local farmers (1).
This would appear to be bad news for those who lay the blame for the problems of mad cow disease (and, for that matter, the foot-and-mouth epidemic) on large scale ‘industrial’ farming practices and the ‘cheap food’ policies of the big supermarket chains.
The newly fashionable methods of traditional farming, trading and butchering now stand accused of transmitting mad cow disease to the robust beef-eaters of rural England. Is this a cause for celebration for the supporters of corporate food production and retailing, or even for the critics of the urban middle classes’ sentimental affinity for organic farming and farmers’ markets? Not so fast.
The authors of the Queniborough report claim that ‘the people with CJD were 15 times more likely to have purchased and consumed beef from a butcher who removed brain from a beast compared with controls who purchased meat from outlets were cross contamination with brain material was not a risk’.
They claim that this result is statistically significant and is therefore very unlikely to be a chance finding. They also concede that ‘on a national basis’, their explanation for the Queniborough cluster ‘is unlikely to explain how all of the people who have developed this disease were exposed to the BSE agent’.
This is only too true. Indeed, their thesis fails even to account for all five of the Queniborough cases – it holds good only for four. Closer inspection of the report reveals an edifice of speculation built on a flimsy empirical foundation.
‘People may not be able to remember what they gave their families to eat 20 years ago’, the authors admit, indicating the problems arising from the fact that interviews with relatives of victims were a key source of information. Though they claim that they sought only to explore ‘the usual patterns of meat consumption’, the scope for error here is enormous and obvious.
The key question – both in Queniborough and nationally – is that, if BSE is transmitted to humans through the consumption of beef, then why have there been so few cases? The vast majority of the consumers of the contaminated beef of the Queniborough butchers have (so far) remained well.
Furthermore, the farming, slaughtering and butchering practices of Queniborough are common to many areas of Britain where no clusters – or even cases – of variant CJD have appeared. Again, cases of CJD have appeared deep in the inner cities far removed from traditional farmer or butchers.
The categorical claims arising from the study of the Queniborough cluster stand in marked contrast to the sober – and little reported – judgements arising from a major investigation by the government’s CJD surveillance unit of the first 51 known cases of variant CJD (2). This failed to produce any link between the disease and eating beef.
The authors concluded that ‘we have found no evidence of dietary, iatrogenic or occupational risk for vCJD’ (3). In response the Department of Health admitted that the evidence that eating beef was to blame for vCJD was ‘circumstantial’.
The speculations of the Leicestershire epidemiologists are an illustration of the fallacy of van Helmont’s tree, as propounded by that great Irish disciple of Wittgenstein, Maurice O’Connor Drury (4).
Jean Baptiste van Helmont (1577-1644) was a Belgian chemist famous for establishing the principle of the conservation of matter and for his precise quantitative methods. In an experiment, he weighed a small ash sapling, some earth and a large pot and then planted the sapling in the pot. He covered the soil and watered it every day with pure distilled water. After some months the tree had grown a hundred fold; van Helmont removed it from the pot, separated it from the soil and once again weighed everything.
Discovering that the soil and the pot had not lost weight, he concluded that all the materials of the tree – the bark, the leaves, the roots, etc – were composed of nothing but water. Van Helmont’s conclusions were understandable at a time when the concepts of photosynthesis (by which plants extract carbon from the carbon dioxide in the atmosphere) and nitrogen fixation (by which micro-organisms in the soil extract nitrogen from the air and transmit it to the plant) were unknown.
‘Now the motto of this’, wrote O’Connor Drury, ‘is that in the early stages of any science when there are still a host of unknown factors at work it can be most misleading to draw conclusions from experiments, however accurately performed’. He warns medical researchers who earnestly flaunt the precision of their statistical techniques – ‘Remember van Helmont’s tree’.
Scientists today have a much better understanding of BSE and CJD than their forebears did of the biology of plants in the seventeenth century. Yet considerable areas of mystery remain.
The lesson of van Helmont’s tree is that scientists need to focus their attention on the underlying biological processes, rather than engaging in wild speculations on the basis of precisely measured, but basically useless, data. This is further justification for a prophylactic (and humanely executed) cull of epidemiologists to curtail further eruptions of panics about mad cow and other diseases (5).
Dr Michael Fitzpatrick is the author of MMR and Autism, Routledge, 2004 (buy this book from Amazon (UK) or Amazon (USA)); and The Tyranny of Health: Doctors and the Regulation of Lifestyle, Routledge, 2000 (buy this book from Amazon UK or Amazon USA). He is also a contributor to Alternative Medicine: Should We Swallow It? Hodder Murray, 2002 (buy this book from Amazon (UK) or Amazon (USA)).
Mad cow panic issue
(1) See Press release, Leicestershire Health Authority, 21 March 2001
(2) CJD and eating beef ‘not linked’, BBC Online, 4 November 2000
(3) See CJD (new var), beef consumption link unproven, ProMED Mail, 4 November 2000
(4) The Danger of Words and Writings on Wittgenstein, 1976, p10-12. Buy this book from Amazon (UK) or Amazon (USA)
(5) Read Epidemiology uncovered by Dr Michael Fitzpatrick
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