The objective of this study is to assess the occurrence of and risk factors for serious infections in rheumatoid arthritis (RA)-associated interstitial lung disease (ILD). All patients with RA-ILD (ACR 1987 criteria for RA) seen at a single center from 1998 to 2014 were identified and manually screened for study inclusion. Follow-up data were abstracted until death or December 31, 2015. Serious infection was defined as requiring antimicrobial therapy and hospitalization. Risk of infection was analyzed by person-year (py) methods using time-dependent covariates started when the medication was first used and stopped 30 days after the medication was discontinued. Of the 181 included patients, 87 (48 %) were female. The mean age at ILD diagnosis was 67.4 (±9.9) years, and median follow-up time was 3.1 (range: 0.01 to 14.8) years. Higher infection rates were observed during the first year after ILD diagnosis (14.1 per 100 py) than subsequently (5.7 per 100 py; p = 0.001). Pneumonia was the most common (3.9 per 100 py). Overall infection risk was higher in organizing pneumonia (OP) (27.1 per 100 py) than usual interstitial pneumonia (7.7 per 100 py) or non-specific interstitial pneumonia (5.5 per 100 py) (p < 0.001). The highest infection rate observed was with a daily prednisone use >10 mg per day (15.4 per 100 py). Patients with RA-ILD are at risk of serious infection. Prednisone use >10 mg per day was associated with higher rates of infection. Immunosuppressive drug use governed by concern for risk of infection in patients with ILD resulting in channeling bias cannot be excluded.
Keywords: Hospitalization; Immunosuppression; Infection; Interstitial lung disease; Rheumatoid arthritis.