Ann Rheum Dis. 2019 Mar;78(3):320-327. DOI: 10.1136/annrheumdis-2018-214326Differences in baseline characteristics and numerical differences in IR of SI between ABA, RRTX and TOZ were observed. The relative risk (RR) of SIs seemed to vary modestly with drug.TNFi treated RA patients in large observational studies have suggested an initial twofold increased risk of SIs compared with biologic-naïve patients. Long-term observational studies on the risk of SIs in patients treated with non-TNFi bDMARDs are sparse.This study aimed to estimate crude as well as age and gender-adjusted IRs of SIs and RR of SIs during 0–12 and 0–24 months since treatment start with ABA, RTX or TCZ.This observational cohort study is conducted in parallel within RA populations in Denmark (DANBIO) and Sweden (ARTIS), who started ABA/RTX/TCZ between 2010-2015. Incidents of SI and potential cofounders were identified through linkage to national registries. Age and gender-adjusted IRs of SI and additional adjusted-RRs of SI during 0–12 and 0–24 months since start of treatment were assessed using Poisson regression.RTX-treated patients were older, had longer disease duration and more previous malignancies, whereas TCZ was associated with higher baseline c reactive protein. The highest IR of infection in the first 12 months was observed in RTX treated patients, followed by ABA and TCZ, but with overlapping confidence intervals. IRs of SIs for patients on RTX was highest during the first 6 months (Denmark: 11.0/100 PY; Sweden: 7.5/100 PY) and TCZ (Denmark: 7.1 /100 PY; Sweden: 5.5/100 PY) and patients treated with ABA in Denmark (9.7/100 PY). ABA-treated Swedish patients had similar IRs from 0–6 and 6–12 months. Differences in RR across the three treatment drugs were observed. Adjustments for age, gender, treatment history, disease duration and co-morbidities had minor effect on RR estimates.Numerical differences in IRs of SIs between ABA, RTX and TCZ were observed. RR of SIs varied with drug (TCZ < ABA < RTX) but should be interpreted with caution due to the few events and the risk of residual cofounding.