Risk of autoimmune diseases in patients with COVID-19: A retrospective cohort study, 2022, Chang et al

Risk of autoimmune diseases in patients with COVID-19: A retrospective cohort study
Renin Chang, Thomas Yen-Ting Chen, Shiow-Ing Wang, Yao-Min Hung, Hui-Yuan Chen, Cheng-Chung James Weic

Background
There are a growing number of case reports of various autoimmune diseases occurring after COVID-19, yet there is no large-scale population-based evidence to support this potential association. This study provides a closer insight into the association between COVID-19 and autoimmune diseases and reveals discrepancies across sex, age, and race of participants.

Methods
This is a retrospective cohort study based on the TriNetX U.S. Collaborative Network. In the test-negative design, cases were participants with positive polymerase chain reaction (PCR) test results for SARS-CoV-2, while controls were participants who tested negative and were not diagnosed with COVID-19 throughout the follow-up period. Patients with COVID-19 and controls were propensity score-matched (1: 1) for age, sex, race, adverse socioeconomic status, lifestyle-related variables, and comorbidities. The primary endpoint is the incidence of newly recorded autoimmune diseases. Adjusted hazard ratios (aHRs) and 95% confident intervals (CIs) of autoimmune diseases were calculated between propensity score-matched groups with the use of Cox proportional-hazards regression models.

Findings
Between January 1st, 2020 and December 31st, 2021, 3,814,479 participants were included in the study (888,463 cases and 2,926,016 controls). After matching, the COVID-19 cohort exhibited significantly higher risks of rheumatoid arthritis (aHR:2.98, 95% CI:2.78–3.20), ankylosing spondylitis (aHR:3.21, 95% CI:2.50–4.13), systemic lupus erythematosus (aHR:2.99, 95% CI:2.68–3.34), dermatopolymyositis (aHR:1.96, 95% CI:1.47–2.61), systemic sclerosis (aHR:2.58, 95% CI:2.02–3.28), Sjögren's syndrome (aHR:2.62, 95% CI:2.29–3.00), mixed connective tissue disease (aHR:3.14, 95% CI:2.26–4.36), Behçet's disease (aHR:2.32, 95% CI:1.38–3.89), polymyalgia rheumatica (aHR:2.90, 95% CI:2.36–3.57), vasculitis (aHR:1.96, 95% CI:1.74–2.20), psoriasis (aHR:2.91, 95% CI:2.67–3.17), inflammatory bowel disease (aHR:1.78, 95%CI:1.72–1.84), celiac disease (aHR:2.68, 95% CI:2.51–2.85), type 1 diabetes mellitus (aHR:2.68, 95%CI:2.51–2.85) and mortality (aHR:1.20, 95% CI:1.16–1.24).

Interpretation
COVID-19 is associated with a different degree of risk for various autoimmune diseases. Given the large sample size and relatively modest effects these findings should be replicated in an independent dataset. Further research is needed to better understand the underlying mechanisms.

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That result looks very odd.

There seems to be about a threefold increase in risk for a whole range of unrelated disorders. Ankylosing spondylitis is not an autoimmune disease and is largely genetically determined, for instance.

I strongly suspect that they picking up on some systematic bias factor to do with who has a positive test and who has a negative test. The retrospective nature of the study is not encouraging.