H Ashraf. Lancet March (2001) Vol. 357 #9620 p. 937.
Five cases of confirmed new-variant CJD have occurred in a geographically small area in Leicestershire. The cases were included in a case control study which established a relative risk of 15 if you purchased and consumed beef from at least one of two butchers who, as standard practice, removed cow brains. Statistical significance was not recorded.
Clustering of cases will occur by chance, but the existence of a plausible link between cases reduces the credibility of this alternative explanation.
The plausible link is founded on the memory of food purchasing and consumption habits over 20-year period. Victims and controls in the study were not equivalent.
9% of butchers (UK) practiced brain removal during the 80’s (no information available for the early nineties when exposure probably peaked). Slaughtering practices were not precisely regulated or enforced until after the BSE epidemic among cattle had peaked.
Some commentators suggest that this study indicates a latency period of 10 years. Though this encourages the view that the total number of human victims will be relatively small, it is still far from certain.
Clusters of cases will provide some encouragement for those who wish to identify a probable source of contamination. Under normal circumstances such identification is usually very difficult.