NR AIVG
AU Neilson,S.
TI Creutzfeldt-Jakob disease and bovine spongiform encephalopathy. Risk to human population is remote.
QU British Medical Journal 1996 Apr 20; 312(7037): 1038-9
KZ BMJ. 1996 Mar 30;312(7034):791-3. PMID: 8608274
PT comment; letter
VT
EDITOR - Many commentaries on bovine spongiform encephalopathy have focused concern on recent unusual cases of Creutzfeldt-Jakob disease, an apparently important increase in the incidence of the disease, and statistical accretions in particular age and occupational groups. A link between the two diseases raises the possibility (even if not the probability) of risk to large numbers of people.[i] Indeed, the standardised mortality ratios for deaths due to Creutzfeldt-Jakob disease reported to the Office of Population Censuses and Surveys during the 15 years 1919-93 show a significant excess in 1992 (chi-squared=11.67, P less than 0.01) and the interval 1987-93 (chi-squared = 4.29, P less than 0.05). The age adjusted mortality rose by 30%, from 0.6 to 0.8 deaths per million.
Deaths from Creutzfeldt-Jakob disease in the two intervals 1979-85 and 1987-93 can also, however, be viewed as two samples taken from a common distribution, with the earlier sample being less complete than the later. The difference between the two distributions of cumulative mortality was minimal (chi-squared=0.151, df=16, P greater than 0.999), and a two by two analysis of the proportion of deaths below age 45 during the two intervals (8.8% and 11%respectively) did not show a significant difference (chi-squared=0.261, df=1, P=0.61). The rise in overall mortality to date is therefore more likely to be attributable to increased awareness of Creutzfeldt-Jakob disease than to an increased risk of death.
Standard survival modelling techniques[ii] indicate that there is a small subpopulation susceptible to death due to Creutzfeldt-Jakob disease, whose relatively high mean age at death could potentially be reduced by exposure to a triggering agent derived from cattle. In particular, the mortality is well fit by a multistage (Weibull) mortality distribution[iii] in which mortality rises as the seventh power of age (for all ages) and the risk of death is restricted to about 70 per million of the general population, or about 3500 people.
[Image]Figure 1 compares the distributions of theoretical and observed mortality in 1979-85 (chi-squared =1.42, df=19, P greater than 0.999) and 1987-93 (chi-squared=0.329 df= 19, P greater than 0.999) and also shows the projected effect of a 50% increase in exposure to risk. Declining mortality after age 67 can be explained by the reduction in the number of susceptible people
The earlier age at onset noted in cases with identified polymorphisms [iv] may merely reflect the difficulties of genetic analysis and detection of familial associations in late onset cases. while bovine spongiform encephalopathy may represent a risk to these select people, there is no evidence that it has done so.
References
ii. Gore S. Bovine Creutzfeldt-Jakob disease? BMJ 1996 312,790-1 (30 March.)
ii. Neilson S, Robinson I. Reinterpreting mortality statistics: some uses of Gompertzian analysis in epidemiological research, J Clin EpidemioI 1993;41:1063-9.
iii. Doll R, The age distribution of cancer: implications for models of carcinogenesis. Journal of the Royal Statistical Society 1971; 134:133-66
iv. Brown P. Transmissible human spongiform encephalopathy (infections cerebral amyloidosis): Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Scheinker syndrome and kuru. In CaIne D B, ed, Neurodegenerative disease. Philadelphia: WB Saunders, 1994:839-76.
ZR 4
MH Adolescent; Adult; Aged; Aged, 80 and over; Child; Creutzfeldt-Jakob Syndrome/*mortality; Encephalopathy, Bovine Spongiform/*transmission; England/epidemiology; Human; Middle Age; Risk Factors; Wales/epidemiology
AD STUART NEILSON Director of medical information systems Centre for the Study of Health, Sickness, and Disablement, Brunel University, Uxbridge, Middlesex UB8 3PH
SP englisch
PO England
OR Prion-Krankheiten 6