Declining trend in the incidence of rheumatoid factor-positive rheumatoid arthritis in Finland 1980-2000.

OBJECTIVE

To investigate trends in the incidence of rheumatoid arthritis (RA) in Finland.

METHODS

We studied all the subjects entitled to receive drug reimbursement for chronic inflammatory joint diseases in 5/21 central hospital districts (population base about 1 million adults) in Finland during 2000. The incidence rates and the mean age at disease onset were compared with those from 1980, 1985, 1990, and 1995.

RESULTS

A total of 714 subjects were entitled to drug reimbursement for chronic inflammatory joint disease that had started at the age of 16 or over. Of them, 321 satisfied the American College of Rheumatology classification criteria for RA, 198 had spondyloarthropathy, and 195 had undifferentiated oligo- or polyarthritis. The incidence of RA was 29.1/100,000 (95% CI 26.0-32.5); the figures for rheumatoid factor (RF)-positive RA and RF-negative RA were 18.2 (95% CI 15.8-21.0) and 10.8 (95% CI 9.0-12.9)/100,000, respectively. The incidence of RA was 36.9 (95% CI 32.1-42.2)/100,000 among women and 20.8 (95% CI 17.2-25.1)/100,000 among men. The age- and sex-adjusted incidence rate ratio declined from 1.00 in the referent year 1980 to 0.55 (95% CI 0.46-0.66) in 2000. A declining trend was evident for the incidence of RF-positive RA (p < or = 0.001).

CONCLUSION

We verified the declining trend for the incidence of RF-positive RA in both sexes in Finland. Although the etiology of RA remains unknown, public health measures may reduce the risk of RA in the general population.