The objective of this study was to examine temporal and regional variations of sporadic Creutzfeldt–Jakob disease (sCJD) in a retrospective study using Japanese national surveillance data from 2001 to 2010. We calculated the incidence of sCJD by age and sex, derived the standardized incidence in each of the 47 prefectures, and performed spatial disease clustering analysis. The average annual incidence of sCJD was 1·026 per million in men (637 patients) and 1·132 per million in women (733 patients), a significant sex difference after adjustment for age (P = 0·001). The ratios of familial CJD to sCJD apparently increased between 2001–2005 and 2006–2010, possibly as a result of the nationwide introduction of genetic testing after 2006. Based on the data of 2006–2010, certain geographical clusters of sCJD were identified. The incidence of sCJD was higher in several specific prefectures compared to the national average. Thus, sCJD appears to have regional variations, suggesting the existence of genetic or region-specific factors affecting the incidence of the disease.

Medico-legal death investigation systems have the potential to play an important role in disease surveillance. While these systems are in place to serve a public function, the degree to which they are independent of central government can vary depending on jurisdiction. How these systems use this independence may present problems for public health initiatives, as it allows death investigators to decline to participate in government-led surveillance regardless of how critical the studies may be to public health and safety. A recent illustration of this problem in the UK is examined, as well as general lessons for removing impediments to death investigation systems participating in public health research.