title: The existence of geographical clusters of cases of inflammatory polyarthritis in a primary care based register.
abstract: OBJECTIVE
  To determine whether there is any evidence that there are spatial clusters of rheumatoid arthritis in particular, and inflammatory arthritis in general.
  
  
  METHODS
  Setting was a population based incidence register of inflammatory arthritis: the Norfolk Arthritis Register (NOAR). All cases identified between 1990-1995 were mapped to place of residence. Statistical evidence of clustering was determined by calculating Poisson probabilities in putative areas.
  
  
  RESULTS
  Three clusters were identified including one small area (population 85) where five unrelated cases developed during this time period. There was no obvious greater disease homogeneity within clusters and no common environmental factors were identified.
  
  
  CONCLUSIONS
  Rare clusters of inflammatory polyarthritis do occur. Their significance and cause remain to be elucidated.
authors.affiliation: ARC Epidemiology Unit, University of Manchester, Stopford Building, Oxford Road, Manchester M13 9PT, UK.
authors.forename: A
authors.initials: A
authors.lastname: Silman
authors.forename: B
authors.initials: B
authors.lastname: Harrison
authors.forename: E
authors.initials: E
authors.lastname: Barrett
authors.forename: D
authors.initials: D
authors.lastname: Symmons
mesh_terms: D000328:Adult; D000368:Aged; D001168:Arthritis / Q000453:epidemiology*; D001172:Arthritis, Rheumatoid / Q000453:epidemiology; D016000:Cluster Analysis; D004739:England / Q000453:epidemiology; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D011320:Primary Health Care; D012042:Registries; D013029:Space-Time Clustering