Prevalence of antibodies against Chlamydia trachomatis and incidence of C. trachomatis-induced reactive arthritis in an early arthritis series in Finland in 2000.

OBJECTIVE: To study the prevalence of different serotypes of Chlamydia trachomatis antibodies and the incidence of C. trachomatis-induced reactive arthritis (ReA) among patients with early arthritis in a defined population.

METHODS: Serum samples were collected from a cohort of 122 adult patients in the age group 18-65 years included in the Kuopio 2000 Arthritis Survey. Antibodies against C. trachomatis serotypes C, E, and G were studied using enzyme immunoassay (EIA) tests among patients and in a control cohort of 78 adults without any joint symptoms. The incidence assessment for Chlamydia-induced ReA was based on a ligase chain reaction (LCR) test in urine and clinical symptoms and signs appropriate for ReA.

RESULTS: Of 122 patients, with the baseline diagnosis of rheumatoid arthritis (RA) in 11, spondyloarthropathy (SpA) in 28, and undifferentiated arthritis (UA) in 83 cases, 42 (34%) showed immunoglobulin (Ig)G or IgA antibodies against at least one serotype C, E, or G. Among the patients with UA the prevalence was significantly increased compared with the controls (p = 0.010). C. trachomatis-induced ReA arthritis was diagnosed in only three patients with the LCR test. On this basis the incidence of C. trachomatis-induced arthritis was 5.4/100 000 [95% confidence interval (CI) 1.1-15.7] in the age group 18-65 years.

CONCLUSION: Antibodies against C. trachomatis were most common in patients with UA reflecting the fact that cases with chlamydia-induced ReA are included in this subgroup.