Do new cases of rheumatoid arthritis cluster in time or in space?

OBJECTIVES: To examine for evidence of clustering in time, in space and in space/time in the occurrence of rheumatoid arthritis (RA). SETTING: A population-based incidence register of RA in the East Anglian region of the UK: population size 413,000. SUBJECTS: In all 687 new cases of inflammatory joint disease registered between 1 January 1990 and 31 December 1994 were studied. Population data were obtained from postcode areas by age and sex. ANALYSIS: Time trend analysis was conducted over the first 36 months and observed and expected distributions compared. Spatial clustering was based on comparison of observed distribution using map grid references to random expectation based on simulation. A similar procedure was undertaken for time/space clustering. RESULTS: There was no evidence of a time trend. There was only modest evidence of spatial clustering with non-random distribution observed in one area but there was no evidence of time/space clustering. CONCLUSION: Although a viral aetiology is the strongest candidate for RA, no evidence of a localized event in time was associated with disease development in this population.