title: A systematic review of sporadic Creutzfeldt-Jakob disease clusters: do clinical, epidemiologic, and genetic features reflect infectious clustering mechanisms?
abstract: BACKGROUND
  While the cause of sporadic Creutzfeldt-Jakob disease (sCJD) is unknown, case clustering could suggest infectious transmission in some instances.
  
  
  METHODS
  Publications of sCJD clusters were systematically identified and pooled to determine if their clinical, epidemiologic, and genetic features reflected potential infectious clustering mechanisms.
  
  
  RESULTS
  The search yielded five clusters involving 23 cases. Most notably, among 12 cases with reported residential histories, patients lived for a median of 30.0 years (25th percentile: 26.5 years; 75th percentile: 51.0 years) in their respective cluster regions. Of 19 cases that underwent genotyping for polymorphic codon 129, seventeen were methionine homozygotes (89.5%; 95% CI 67.4-98.3%); none were heterozygous.
  
  
  CONCLUSIONS
  Prolonged residency duration and Prnp codon 129 methionine homozygosity may be consistent with underlying disease-clustering mechanisms, although larger, controlled investigations might help to exclude the possibility that these findings reflect the normal distribution of these features among relevant comparison populations.
authors.affiliation: Department of Medicine, Hospital of St. Raphael, New Haven, USA. jedbarash@hotmail.com
authors.forename: Jed A
authors.initials: JA
authors.lastname: Barash
authors.forename: James
authors.initials: J
authors.lastname: Dziura
mesh_terms: D016000:Cluster Analysis; D007562:Creutzfeldt-Jakob Syndrome / Q000453:epidemiology* / Q000235:genetics / Q000635:transmission; D005838:Genotype; D006801:Humans; D012111:Residence Characteristics; D012307:Risk Factors; D013997:Time Factors