When did bovine spongiform encephalopathy (BSE) start?
CH Cohen and AJ Valleron INSERM-Unite 444 Epidemiologie et Sciences de l’Information, Institut federatif Saint-Antoine de Recherches sur la Sante, faculte de Medecine Saint-Antoine, Paris, France. BACKGROUND: Knowing the starting date of the BSE epidemic and its size at the very beginning is crucial to interpret the timing of the nvCJD cases and to forecast the nvCJD epidemic. The first cases occurred in 1985. The models devised by Anderson (back-calculation) and Dealler (age-period-cohort) led to an estimate of less than 50 cases in 1983, and none earlier. Here, we applied age-cohort models to the BSE data in order to estimate the earliest possible date of the first unrecognized BSE cases. METHODS: The numbers of confirmed BSE cases in the UK, by age group and by calendar year from 1988 to 1996, were analysed by Poisson regression. The cases’ age distribution was considered as constant between the different birth cohorts. The herd’s age structure was taken into account. RESULTS: Accor
