Geographical distribution of variant CJD in the UK (excluding Northern Ireland)

Background The agent that causes variant Creutzfeldt-Jakob disease (variant CJD) is indistinguishable from the causative agent of bovine spongiform en cephalopathy (BSE). The transmission route by which human beings are infect ed has not been established. One hypothesis is that cases of variant CJD ha ve resulted from exposure to the BSE agent via rendering plants involved in the production of meat and bone meal, the main vehicle of the BSE epidemic . Methods We identified cases of variant CJD through the National CJD Surveil lance Unit, and obtained lifetime residential histories of cases by intervi ewing a relative. The addresses of all rendering plants in the UK (excludin g Northern Ireland) in production in 1988 were available from a survey done in that year. We calculated the distance between each case's place of resi dence on Jan 1, 1988, and the nearest rendering plant from postcode data, a nd used data from the 1991 UK census to estimate the population living with in various distances of rendering plants. We compared the observed number o f cases of variant CJD within a particular distance of a rendering plant wi th the number expected if there is no association between residential proxi mity to a rendering plant and the risk of developing variant CJD. Findings Up to Aug 31, 1998, 26 cases of variant CJD with onset in the UK ( Northern ireland not included) had been identified. The observed and expect ed numbers of variant CJD cases living within a specified distance of any r endering plant up to 50 km were almost the same. Two plants in the county o f Kent each had four cases within 50 km in 1988, significantly more cases t han expected (plant A, 1.04 expected; plant B, 0.74 expected). Multiple sig nificance tests were done, so some tests would be expected to appear signif icant by chance alone. Computer simulations suggested that the observation of four cases of variant CJD living in an area with a population of 1.5 mil lion (the size of Kent) is not unexpected. Interpretation There is no evidence that people with variant CJD tended to live closer than the population as a whole to rendering plants in the 1980s . The reported cluster of variant CJD cases in Kent is most probably a chan ce finding.