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OBJECTIVE: To determine time trends in the epidemiology of rheumatoid arthritis (RA) in a population-based cohort. METHODS: An inception cohort of residents of Rochester, Minnesota > or = 18 years of age who first fulfilled the American College of Rheumatology 1987 criteria between January 1, 1955 and December 31, 1994 (applied retrospectively, as appropriate) was assembled and followed up until January 1, 2000. Incidence rates were estimated and were age- and sex-adjusted to the 1990 white population of the US. A birth cohort analysis was performed, and survival rates over time were examined. RESULTS: The incidence cohort comprised 609 patients, 445 (73.1%) of whom were female and 164 (26.9%) were male, with a mean age at incidence of 58.0 years. The overall age- and sex-adjusted annual incidence of RA among Rochester, Minnesota, residents > or = 18 years of age was 44.6/100,000 population (95% confidence interval 41.0-48.2). While the incidence rate fell progressively over the 4 decades of study, from 61.2/100,000 in 1955-1964, to 32.7/100,000 in 1985-1994, there were indications of cyclical trends over time. Birth cohort analysis showed diminishing incidence rates through successive cohorts following a peak in the 1880-1890 cohorts. Incidence rates increased with age until age 85, but peaked earlier in women than in men. The survival rate in RA patients was significantly lower than the expected rate in the general population (P < 0.001), and no improvement was noted over time. CONCLUSION: The secular trends demonstrated in this study population, including the progressive decline in the incidence of RA over the last 40 years, suggest that an environmental factor may play a role in the etiology of RA.
Doran et al. (Fri,) studied this question.