Low positivity rate in antibody SARS-CoV2 tests in patients with rheumatic diseases treated with rituximab. a case control study of a high impact SARS-CoV2 infection area

García Fernández, A.; Morán Álvarez, P.; Bachiller-Corral, J.; Vázquez Díaz, M.

Background: Diagnosis of previous SARS-COV2 infection may be challenging in immunocompromised patients. Objectives: To analyze positivity rate to SARS-COV2 antibody tests (SC2AT) in patients diagnosed of rheumatic diseases (RMD) treated with Rituximab. Methods: We conducted a case-control study of patients diagnosed of RMD followed in a referral hospital in Madrid, Spain. Positivity rate to IgG-SC2AT were analyzed in Rituximab-treated patients (RTX) compared with patients treated with TNF inhibitors (TNFi) and/or conventional DMARDs (cDMARDs) (N-RTX). We included patients that received Rituximab in the previous year to a confirmed SARS-COV2 infection (defined as a positive polymerase chain reaction test (PCR) and/or compatible chest Xray), to a suspected SARS-COV2 infection (2 or more symptoms) or to SC2AT determination. Patients with RMD treated with other biological DMARDs (bDMARDs) rather than Rituximab or TNFi were excluded. Results: We included 152 patients with RMD who underwent a SC2AT. Main characteristics are reported in Table 1. Among RTX and N-RTX, 4/48 (8.3%) and 35/104 (33.7%) showed a positive IgG-SC2AT, respectively. Four out of 104 (38.5%) N-RTX tested positive without previous symptoms. No asymptomatic infection was diagnosed among RTX. Univariable analysis showed a lower rate of positivity to SC2AT in confirmed and suspected infection among RTX [Positive IgG-SC2AT in confirmed infection: RTX 4/10 (40%), N-RTX 16/20 (80%);p=0.045. Positive IgG-SC2AT in suspected infection: RTX 0/3 (0%), N-RTX 15/18 (83.3%);p=0.015]. A logistic binary regression identified previous symptoms [OR 61.2, 95CI(13.3-280.6) p=0.0001], male sex [OR 4.8, 95CI(1.3-17.8) p=0.02], non-rituximab treatment [OR 19.7, 95CI(3.6-106.3) p=0.001] as independent factors associated with a higher probability of positive IgG-SC2AT. Age, previous PCR status, corticosteroid and cDMARD use showed no statistical significance. This model accounted for 47.6% of positive cases. Conclusion: RTX had a lower rate of positivity to IgG-SC2AT compared to N-RTX. Previous symptoms, male sex and non-RTX treatment were independently associated with higher probability of positive IgG-SC2AT.