Objective: To describe trends in the epidemiology of rheumatoid arthritis (RA) over a period of 30 years in a population-based cohort.
Methods: An inception cohort of Rochester, Minnesota residents who were > or =35 years of age and had RA (as defined by the 1987 American College of Rheumatology criteria for RA) first diagnosed between January 1, 1955 and January 1, 1985 was assembled and followed up until January 1, 1995. Incidence rates were age- and sex-adjusted to the 1970 US white population. Prevalence of RA in this cohort was estimated on January 1, 1985. A birth-cohort analysis was performed by calculating and comparing incidence rates in each of 16 birth cohorts.
Results: Of the 425 Rochester residents who fulfilled the inclusion criteria, there were 113 men (26.6%) and 312 women (73.4%), with a mean age at diagnosis of 60.2 years. The mean followup time was 15.1 years. The overall age- and sex-adjusted annual incidence of RA among Rochester, Minnesota residents > or =35 years of age (1955-1985) was 75.3 per 100,000 population (95% confidence interval 68.0-82.5). This incidence was approximately double in women compared with that in men and increased steadily with age, until age 85, after which the incidence of RA decreased. Secular trends in the incidence of RA over the entire study period were demonstrated. The overall prevalence of RA on January 1, 1985 was approximately 1%. The birth-cohort analysis showed peak incidence rates in the 1880-1895 birth cohorts.
Conclusion: The epidemiology of RA is dynamic. The findings in this study lend further support to the hypothesis of a host-environment interaction in the pathogenesis of RA.