title: Decreasing incidence and prevalence of rheumatoid arthritis in Pima Indians over a twenty-five-year period.
abstract: OBJECTIVE
  To evaluate temporal trends in the incidence of rheumatoid arthritis (RA).
  
  
  METHODS
  Incident cases of RA were identified among a population-based cohort of Pima Indians in Arizona over the period 1965-1990.
  
  
  RESULTS
  Among 2,894 subjects, 78 incident cases of RA were identified. The age-adjusted incidence declined by 55% in men (Ptrend = 0.225), and by 57% in women (Ptrend = 0.017) after controlling for oral contraceptive or estrogen use and for pregnancy experience. During the same period, age-adjusted prevalence rates of active RA decreased by 29% in men (Ptrend = 0.63) and by 40% in women (Ptrend = 0.02). Fewer than 17% of subjects with known RA were taking slow-acting antirheumatic drugs (SAARDs) in 1990.
  
  
  CONCLUSIONS
  The decrease in incidence and prevalence of RA in this population over such a short period implicates the involvement of an environmental factor(s), other than exogenous estrogens, in the pathogenesis of the disease. However, the possibility that the observed decrease might be explained by an increased use of SAARDs in subjects with RA cannot be excluded.
authors.affiliation: National Institute of Arthritis and Musculoskeletal and Skin Diseases, Phoenix, Arizona.
authors.forename: L T
authors.initials: LT
authors.lastname: Jacobsson
authors.forename: R L
authors.initials: RL
authors.lastname: Hanson
authors.forename: W C
authors.initials: WC
authors.lastname: Knowler
authors.forename: S
authors.initials: S
authors.lastname: Pillemer
authors.forename: D J
authors.initials: DJ
authors.lastname: Pettitt
authors.forename: D R
authors.initials: DR
authors.lastname: McCance
authors.forename: P H
authors.initials: PH
authors.lastname: Bennett
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001130:Arizona / Q000453:epidemiology; D001172:Arthritis, Rheumatoid / Q000453:epidemiology*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D015994:Incidence; D007198:Indians, North American / Q000706:statistics & numerical data; D008297:Male; D008875:Middle Aged; D015995:Prevalence