High seroprevalence of anti-HTLV-I antibody in rheumatoid arthritis

Objective. To investigate the association between human T lymphotropic virus type I(HTLV-I) infection and rheumatoid arthritis (RA) in Nagasaki, an area highly endemic for HTLV-I infection. Methods. Sera from 113 female patients with RA and 19,796 female blood donors were screened for anti-HTLV-I antibodies with a gelatin particle agglutination kit and confirmed using an immunoblotting kits. Results. The age-adjusted summary odds ratio of HTLV-I infection among RA patients, as compared with blood donors, was 2.8 (95% confidence interval [95% CI] 1.8-4.6). The etiologic fraction, i.e., the proportion of RA in the study population that is attributable to HTLV-I infection, was estimated to be 13.2% (95% CI 5.1-21.2). There was no significant difference in the clinical and laboratory findings between HTLV-I-infected and HTLV-I-uninfected RA patients. Conclusion. These epidemiologic findings support the idea that HTLV-I infection is a risk factor for RA, and suggest that similar to 13% of the cases of RA in females living in Nagasaki are associated with HTLV-I infection.