Risk of active tuberculosis in patients with inflammatory arthritis receiving TNF inhibitors: a look beyond the baseline tuberculosis screening protocol

Tuberculosis (TB) is a major concern in patients receiving TNF inhibitors (TNFi). This study aimed to assess the incidence of active TB and the efficacy of TB prevention measures used over the years, and to determine risk factors for developing TB, in a single-centre cohort of patients with rheumatoid arthritis (RA), psoriatic arthritis (PsA) and ankylosing spondylitis (AS) receiving TNFi. Data of all patients in whom treatment with TNFi was initiated in our rheumatology clinic until December 1st 2014 have been retrospectively analysed. The cohort was divided into 3 groups per the mandatory LTBI screening method at baseline: tuberculin skin test (TST) with a positive threshold of either 10 mm (group TST1), or 5 mm (group TST2), and QuantiFERON®-TB Gold test (group QFT). The incidence of active TB was analysed for each group and compared to TB incidence data in general population. Five hundred fifty patients were included (305 RA, 42 PsA, 203 AS); 97 patients belonged to the TST1, 229 to the TST2 and 224 to the QFT group. The number of active TB cases/time of exposure to TNFi (person-years, PY) was 8/593.5, 9/1044.0 and 3/555.3, respectively, accounting for an incidence of 1348.0, 862.1 and 540.2 cases per 10⁵ PY. Active TB cases occurring in the first year of TNFi treatment (early TB) per total TB cases were only 3/8, 1/9 and 1/3, respectively, too few to identify statistically significant differences between the 3 LTBI screening protocols. However, less TB cases per total observation time were registered in the QFT group, probably due to the reduced duration of exposure to TNFi. All cases of active TB were registered among patients receiving monoclonal antibodies TNFi agents. We have found no significant risk factors for developing active TB. In our cohort, TB occurring after 1 year of TNFi treatment exceeds ‘early TB’, suggesting the necessity of further TB prevention measures besides baseline screening for LTBI.