Response to: 'Correspondence on 'Onset of rheumatoid arthritis after COVID-19: coincidence or connected?'' by Roongta et al .

We thank Roongta et al 1 for the interest taken in our work and for bringing this interesting case of seropositive rheumatoid arthritis (RA) after COVID-19 to the attention. They describe a patient who developed polyarthritis after proven SARS-CoV-2 infection, with seroconversion for both rheumatoid factor (RF) and anti-citrullinated protein antibodies (ACPA) between 2 weeks and 6 months after infection. This raises the question whether seroconversion (becoming seropositive for ACPA and RF) might occur more often after COVID-19. In our study, three out of five patients presenting with polyarthritis post-COVID were already autoantibody positive at first presentation to the rheumatologist, on average 8.3 weeks after COVID-19.2 Unfortunately, there was no serum available from the time before COVID-19 or from timepoints between SARS-CoV-2 infection and presentation to the rheumatologist, precluding any investigation into seroconversion after COVID-19 in these patients. However, detailed investigations into the characteristics of their ACPA response revealed the presence of multiple ACPA isotypes …