vCJD epidemiology
Figure 2 is a plot of number of deaths per year by birth cohort (i.e. those victims born before 1970, those born in the 1970s and those born in the 1980s).
Table 1 gives the median age at death of UK victims of definite or probable vCJD for those years for which a median could sensibly be calculated. The overall median age at death is 28 years, with a range from 14 to 75 years. The median number of days from onset of the disease to diagnosis is 326 days, with a further 87 days to death.
(The median is a type of average that is more appropriate than the mean when data is skewed in one direction or the other. If the number of data points is odd, the median is the value of the middle one. If it is even, then it is the mean of the middle two.)
(i)
Compare the shapes of the plots of number of deaths annually for the three age cohorts (Figure 2) with one another and with the distribution for the total number of deaths annually (Figure 1).
(ii)
On the basis of this data, what can be said about the course of vCJD from time of infection to death? Bearing in mind that vCJD is widely believed to affect younger people particularly, what does the data on the youngest age cohort suggest about the vulnerability of the very young to vCJD? In each case, explain the reason(s) for your answer.
