Background: Asthma is a common, non-infectious respiratory disorder affecting roughly 235 million people worldwide. It is of public health importance as it is associated with declining lung function and, in severe cases, mortality. Studies examining the association between asthma and incident autoimmune diseases (IADs) have reported conflicting findings. This may be due to heterogenous definitions of asthma and IADs used in the various epidemiologic studies, the complexity of diagnosing asthma in real world settings, and the use of unvalidated autoimmune outcome algorithms. We examined similar associations between asthma and select IADs using validated algorithms.
Objectives: To evaluate the association between asthma and the incidence of new-onset IADs.
Methods: We used the Optum Clinformatics US health insurance claims database to perform a population-based cohort study examining the incidence rates (IRs) of 4 IADs in patients with and without asthma from January 1, 2016 to March 1, 2020. Asthma was defined as ≥2 International Classification of Diseases version 10 (ICD-10) asthma diagnoses (L20.0, L20.81, L20.82, L20.84, L20.89, L20.9) at least 30 days apart. The outcomes were autoimmune hepatitis (AIH), inflammatory bowel disease (IBD), rheumatoid arthritis (RA), and systemic lupus erythematosus (SLE), identified using validated algorithms based on ICD-10 codes with positive predictive values ≥ 0.83. We used asthma and non-asthma cohorts matched 1:1 on age, sex, race, and calendar year of cohort entry. Poisson regression models adjusted for age, sex, time of cohort entry, diabetes, and oral/topical steroid use to estimate IRs and incident rate ratios (IRRs) with 95% confidence intervals (95% CI).
Results: There were 1,194,942 patients included in the analyses. The adjusted IRs per 100,000 person-years among patients with and without asthma were 18.84 (95% CI 16.3,21.77) and 12.79 (95% CI 10.39,15.75) respectively for AIH, 43.84 (95% CI 39.85,48.23) and 23.25 (95% CI 19.91,27.14) for IBD, 342.1(95% CI 330.61,354) and 175.13 (95% CI 165.53,185.29) for RA, and 20.43 (95% CI 17.6,23.73) and 9.88 (95% CI 7.65,12.75) for SLE.
Conclusions: Our study found that patients with asthma, compared to patients without asthma had a higher incidence of AIH, IBD, RA, and SLE even after adjustments for age, sex, time of cohort entry, diabetes, and steroid use. Further investigations should be conducted to determine if this association differs by asthma severity.