Effects of COVID-19 on Autoimmune Disease Incidence and DMARD Utilization: Evidence from Japanese Insurance Claims Data

Background This matched cohort study utilized a nationwide insurance claims database from Japan, covering approximately 16% of the population across five prefectures. Methods Propensity score matching was employed to create 3,098,948 matched pairs based on age, sex, the Charlson Comorbidity Index, and individual comorbidities. The primary outcome was a composite endpoint of disease-modifying antirheumatic drug (DMARD) prescriptions, including biological, conventional synthetic, targeted synthetic, and COVID-specific drugs. The secondary outcomes included the incidence of various autoimmune and inflammatory conditions. Participants were required to have continuous healthcare access from January 2020 to December 2022, with a 1-year look-back period. The follow-up period was extended from the COVID-19 index month to December 31, 2022. Incidence rate ratios were calculated to assess the association between COVID-19 and subsequent autoimmune conditions or DMARD use. Results COVID-19 patients had a 33% higher incidence rate of DMARD prescriptions than controls (IRR: 1.33, 95% CI: 1.28–1.38). Subgroup analyses revealed stronger associations among males, younger age groups, and those with multiple comorbidities. COVID-19 infection is also associated with an increased risk of arthritis (IRR: 1.15, 95% CI: 1.13–1.18), glomerulonephritis (IRR: 1.08, 95% CI: 1.05–1.12), respiratory disorders (IRR: 1.49, 95% CI: 1.45–1.53), and other autoimmune conditions. These findings suggest a significant long-term impact of COVID-19 on healthcare utilization for managing autoimmune and inflammatory diseases. Conclusions This study highlights the need for the early identification and management of individuals at risk for post-COVID inflammatory sequelae and ensuring equitable access to DMARD therapies. Further research is warranted to elucidate the underlying mechanisms and develop targeted interventions to mitigate the long-term burden of COVID-19 on the healthcare system.