Failures of epidemiology must be remedied

Britain's Creutzfeldt-Jakob Disease Surveillance Unit was set up in 1990 to alert the Department of Health and the government's Spongiform Encephalopathy Advisory Committee (SEAC) to any changes that might suggest that humans were affected by exposure to the agent responsible for bovine spongiform encephalopathy (BSE). These would include changes in age specific incidence, occupational distribution, or dietary correlates of cases of Creutzfeldt-Jakob disease. Presentation, if it happened at all, was considered more likely to be atypical, but this could not be described in advance. The surveillance unit has fulfilled its remit spectacularly and speedily: a previously unrecognised and consistent disease pattern in young adults has been found, the most likely explanation for which is exposure to the bovine spongiform encephalopathy agent, most probably (but not necessarily) before specified bovine offals were banned in 1989.

Since 1 May 1990, 10 cases of Creutzfeldt-Jakob disease have been reported in people under the age of 42. It is important to put these 10 cases in a broad epidemiological context. We have three estimates of the incidence of sporadic Creutzfeldt-Jakob disease for people aged 15-39: 0.05 per million person years,1 (the same as for people aged 40-44 years2), giving an expected number of 6.3 cases in the six years since 1 May 1990; 0.0286 per million person years, based on three sporadic cases of Creutzfeldt-Jakob disease in this age group reported from 1985 to 1989 (RG Will, personal communication), giving an expected number of 3.6 cases; or a previous guesstimate of 0.01 per million person years,2 (one fifth the incidence at age 40-44), giving an expected number of 1.26 cases. Against each of these expectations, the probability of 10 or more sporadic cases of Creutzfeldt-Jakob disease occurring in people aged 15-39 in the six years from 1 May 1990 is 11 …