Incidence if autoimmune inflammatory rheumatic diseases after COVID‐19 in South Korea: A nationwide cohort study based on health insurance data

Abstract

Many medical issues have arisen in the wake of the coronavirus disease 2019 (COVID-19) pandemic, which was caused by SARS-CoV-2.The risk of thromboembolism increased after SARS-CoV-2 infection, as did the mortality rate. [1][2][3] Moreover, SARS-CoV-2 infection has many sequelae, including immune, nervous, cardiac, respiratory, renal, musculoskeletal, and gastrointestinal abnormalities. 4 A recent study from Hong Kong reported that COVID-19 increased the risk of developing autoimmune inflammatory rheumatic diseases (AIRDs) such as rheumatoid arthritis (RA), spondyloarthritis (SpA), and vasculitis 5 ; however, the hazard ratio (HR) for AIRDs such as systemic lupus erythematosus (SLE), primary Sjogren's syndrome (pSS), and systemic sclerosis (SSc) did not increase significantly in those with COVID-19. 5 Viral infection, a known environmental trigger, can cause AIRDs through several mechanisms, including molecular mimicry, epitope spreading, and bystander activation 6 ; however, additional clinical data are required to clarify the association between infection by SARS-CoV-2 and the occurrence of AIRDs.Here, we used Korean National Health Insurance Service (NHIS) data to compare the incidence of AIRDs between those with a diagnosis of COVID-19 and those without. | MATERIAL S AND ME THODS | Data source and the study populationReimbursement claims data were obtained from the Korean NHIS database; the NHIS covers 97.2% of the Korean population. The National Health Information Database collects NHIS data, including all healthcare-related information such as health screening, socioeconomic and demographic variables, mortality data, diagnoses, and associated procedures and prescriptions, all of which are identified using the International Classification of Diseases, Tenth Revision (ICD-10) codes, as well as Korean Drug and Anatomical Therapeutic Chemical Codes for the entire population. 7 Data from patients who were tested for COVID-19 by RT-PCR (nasal or pharyngeal swabs) from January 2020 to December 2021 were extracted from the NHIS database (approval no. NHIS-2023-1-479) and then divided into COVID-19 PCR (+) and (−) groups. Participants who had ICD-10 codes for AIRDs prior to the COVID-19 PCR assay, or lacked demographic data, were excluded. The index date was the day on which the COVID-19 PCR test was performed, and the end of the follow-up was dated as follows: (1) March 31, 2022, (2) the date on which the first ICD-10 code for AIRDs was issued, or (3) the expired date. In the case of multiple AIRDs codes, the first AIRD code date was taken as the end of follow-up. When individual subjects had undergone multiple COVID-19 PCR assays, the first COVID-19 PCR assay date was used as the index date for the COVID-19 PCR (−) group, and the date of the positive COVID-19 PCR test was used for the COVID-19 PCR (+) group. When the participant was negative for COVID-19 PCR initially and then converted to positive in the latter COVID-19 PCR test, this participant was included in the COVID-19 PCR (+) group, and the index date was ...