Chronic osteomyelitis as a risk factor for development of rheumatoid arthritis: a nationwide, population-based, cohort study.

An association between occult infection and the development of rheumatoid arthritis (RA) has been suggested. This study aimed to determine if patients with chronic osteomyelitis (COM) are at increased risk of developing RA. A national insurance claim dataset of 22 million enrollees in Taiwan was used to identify 21,105 hospital inpatients with COM and 84,420 reference subjects matched by sex, age, and index date of diagnosis with a mean of 5.12 years of follow-up from 2000 to 2011. The risk of RA development was analyzed using Cox proportional hazards modeling. The mean age of hospital inpatients with COM was 55.8 ± 19.4 years. The incidence of RA was 5.43 per 10(4) person-years in the case cohort, which was more than twofold higher than that of 2.20 per 10(4) person-years in the reference cohort. After adjustment, the hazard ratio (HR) was 2.21 (95 % confidence interval, 1.51-3.24). The HR was greatest in the youngest age group (<45 years, HR [95 % confidence interval] = 9.08 [3.22-25.6]; 45-64 years, 1.76 [1.01-3.06]; ≥65 years, 1.68 [0.88-3.24]). In addition, HR was greatest in inpatients with more severe COM (HR [95 % confidence interval] = 0.72 [0.40-1.30] and 11.2 [6.63-18.9] for patients with ≤1 or >2 hospitalization due to recurrent osteomyelitis every two follow-up years, respectively). This is the first report linking COM to risk of incident RA. Patients of a younger age and with frequently recurrent COM had a greater increase in RA risk.