The excess of childhood leukaemia near Sellafield: a commentary on the fourth COMARE report

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Abstract
Problems in investigating disease clusters are illustrated by the latest (fourth) report of the Committee on Medical Aspects of Radiation in the Environment (COMARE) on the excess of leukaemia and non-Hodgkin lymphoma among young people living near the Sellafield nuclear installation in West Cumbria, England. COMARE found no evidence that exposure to radiation could account for this excess and examined alternative explanations. The Report discusses inter alia the hypothesis that these diseases have an infective aetiology promoted by population mixing and considers the relevance of such mixing to the Sellafield area. It concludes that infection cannot be the sole explanation for the excess of cases, implying that some other causative factor (possibly radiation) must also be operating. This conclusion is, however, largely the result of arbitrarily concentrating attention on the village of Seascale (where the excess had initially been observed) rather than the entire vicinity of Sellafield, the putative cause of the excess. This well known pitfall exaggerates the significance of the Seascale excess. The Report then contrasts the magnitude of this excess in Seascale with those in much larger study areas away from Sellafield that were chosen (independently of leukaemia data) because of their relevance to population mixing; but this is not a comparison of like with like. When the Report does consider an area that includes Sellafield, the area chosen is so large (over 700 sq miles) as to `dilute out' localised excesses. COMARE underestimates the special factors that would account, under the infection hypothesis, for the unusually large excess in Seascale, and pays insufficient attention to other communities near Sellafield which may have been affected by population mixing.