Incidence of inflammatory joint diseases in Finland: results from a population-based epidemiological study

The objective of the study was to assess the incidence of inflammatory joint diseases and possible environmental factors contributing to their occurrence in a defined population in Finland. All rheumatologists practising in the Northern Savo rheumatological outpatient departments collected data on their newly diagnosed patients with an inflammatory joint disease in 2010. Antibodies to Aggregatibacter actinomycetemcomitans (Aa) and Porphyromonas gingivalis (Pg) were determined from patients with various arthritides. The incidence of all arthritis cases was 141.8/100,000 (95% CI 126.1-159.1). Eighty-six patients, 43 men and 43 women, satisfied the ACR/Eular 2010 classification criteria for rheumatoid arthritis (RA) yielding an annual incidence of 41.6/100,000 (33.3-51.4), 42.5 (30.8-57.3) for men and 40.8 (29.9-56.1) for women. The incidence of chronic spondyloarthritides was 36.3 (28.6-45.5), reactive arthritis 7.8 (4.4-12.6), undifferentiated arthritis 38.7 (30.7-48.2), and crystalline arthritis 15.0 (10.2-21.3). Immunoglobulin A (IgA) antibody levels to Pg were higher among men, patients with anti-cyclic citrullinated peptide antibodies (ACPA) or missing teeth and AaIgA antibody levels in patients with missing teeth. In RA, 67 % of men and 35% of women had a smoking history, p = 0.012. There was no difference between the genders in the incidence of RA, which might be explained by a higher carriage of periodontal bacteria and a higher smoking rate among men. In other disease categories, the incidences were comparable to those earlier reported. By influencing behavioral and environmental factors, it might be possible to reduce the burden of ACPA-positive RA.