Estimation of epidemic size and incubation time based on age characteristics of vCJD in the United Kingdom

The size of the variant Creutzfeldt-Jakob Disease (vCJD) epidemic in the Un ited Kingdom is a major public health concern and a subject of speculation. The cases are young (mean age = 28). Assuming that the risk of developing the disease in susceptible exposed subjects decreases exponentially with ag e after age 15, that all infections occurred between 1980 and 1989, and tha t the distribution of the incubation period is lognormal, we estimate that the mean duration of the incubation period is 16.7 years [95% confidence in terval (CI): 12.4 to 23.2] and that the total number of cases will be 205 ( upper limit of the 95% CI: 403).