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• Objectives: to estimate the seroprevalence of SARS-CoV-2 infection in patients with rheumatic diseases and to specify the proportion of asymptomatic and symptomatic forms of COVID-19. • Methods: we screened for SARS-CoV-2 infection among spondyloarthritis (SpA, n=143) or rheumatoid arthritis (RA, n=140) patients in our outpatient clinic at Cochin Hospital in Paris between June and August 2020. We performed a qualitative SARS-CoV-2 serological test which detects IgG directed against the N nucleocapsid protein (anti-N) and, for some patients, against the Spike protein (anti-S). Descriptive analyses were managed. • Results: during June–August 2020, the SARS-CoV-2 seroprevalence rate in our population was 2.83% (8/283 patients) without significant difference between RA and SpA patients (2.14% and 3.5% respectively). We report 11 out of 283 patients (3.8%) with a diagnosis of SARS-CoV-2 infection. Among these 11 patients, 1 patient was asymptomatic (9%) with a confirmed diagnosis of COVID-19 by anti-S serology. Of the 283 patients, 85% were under bDMARDs, mainly on rituximab (RTX) (n=44) and infliximab (IFX) (n= 136). • Conclusions: the seroprevalence of SARS-CoV-2 in patients with rheumatic diseases, mainly under bDMARDs treatments, was 2.83%. Among infected patients, 9% were asymptomatic. Detecting SARS-CoV-2 infections could be based on the strategy using patients’ interview and anti-N serology.