Risk of mycobacterial infections associated with rheumatoid arthritis in Ontario, Canada

Objectives — Patients with rheumatoid arthritis (RA) are at increased risk of tuberculosis (TB). Little is known regarding the risk of nontuberculous mycobacterial (NTM) disease in these patients. We sought to ascertain the rate of NTM infection and TB in all residents of Ontario, Canada, with and without RA.

Methods — In a cohort study, all Ontarians aged ≥15 years in January, 2001 were followed until December, 2010. Individuals with RA were identified using a validated algorithm to search hospitalization and physician billing claims. We linked Public Health Ontario Laboratory data to identify all cases of laboratory-confirmed TB and NTM disease. Analysis was performed using Cox proportional hazards regression.

Results — We identified 113,558 Ontarians with RA and 9,760,075 Ontarians without RA. Relative to the non-RA group, adjusted hazard ratios (95% CI) for TB (1.92 (1.50-2.47)) and NTM disease (2.07 (1.84-2.32)) demonstrated increased risks in the RA group. Among those with RA, per 100,000 person years, NTM disease (41.6 (37.1-46.5)) was more common than TB (8.5 (6.5-10.8)). After full adjustment, persons with RA who developed NTM disease were 1.81 times as likely to die as uninfected persons with RA.

Conclusions — Mycobacterial infections are more common in Ontarians with RA, with NTM disease more likely than TB. NTM disease is associated with an increased risk of death in RA patients. Given the rising rates of NTM disease worldwide, determining whether this risk is due to the use of immunosuppressive medications versus RA itself is an important objective for future research.