We thank Rosenbaum et al 1 for their correspondence on our article.2 In their reply, they largely report updated results of COVID-19 occurrence and subjective patient-reported COVID-19 severity from their patient survey of adult patients with spondyloarthritis and specifically comment that in their analysis, sulfasalazine did not ‘increase the risk to develop COVID-19’, nor did it increase the severity of those who were infected. Unfortunately, no details of the statistical methods, including any additional statistical adjustments (eg, age, sex, comorbidities and disease activity) or details of missing data, were included, and only a point estimate of risk was provided for each therapy without CIs, only p values, which therefore limits interpretation. While it is important to share reports of outcomes of COVID-19 among our populations of patients with rheumatic and musculoskeletal diseases (RMDs), it must be pointed out that the survey presented, as well as the subsequent analysis, is fundamentally different from our report on COVID-19-related mortality set within the Global Rheumatology Alliance (GRA) provider database and therefore the two outputs should not be compared, either directly or indirectly.

First, the GRA database is based on physician reports of COVID-19 among patients with known rheumatic disease and therefore can only be used to look at the associations between demographic and clinical features and COVID-19 outcomes among those known to have COVID-19. The data cannot be used to look at factors associated with acquisition of SARS-CoV-2 infection or development of COVID-19 disease, which is the focus of the report presented in the correspondence. These factors should not be compared since restricting the analysis to patients with an existing COVID-19 diagnosis may cause relationships between any variables that relate to COVID-19 acquisition to be distorted compared with a more general population, due to collider bias.3 Indeed, factors associated with …