COVID-19 Associations With Thyroid Disease in Active-Duty Service Members: A Retrospective Cohort Study

There are bidirectional associations between COVID-19 and thyroid disease; little is known about these risks among active-duty service members (ADSM). This study seeks to understand the associations between COVID-19 and thyroid disease in this population and in non-active-duty adults within the military health system.

The researchers conducted a retrospective propensity score-matched cohort study using the Military Health System Database including individuals 18-64 years of age. International Classification of Diseases, 10th revision codes and laboratory results identified COVID-19 infections from July 2020 to June 2021. Patients with COVID-19 were matched 1:2 to controls based on age, sex, beneficiary type, month, and a propensity score. Thyroid disease was identified by ICD-10 codes and those with a thyroid diagnosis in the year prior were excluded. Hazard ratios (HR) and Bonferroni-adjusted 95% confidence intervals (95BoCI) were calculated.

There were 103,778 exposures and 207,556 controls among ADSM and 125,399 exposures and 250,798 controls among non-ADSM. Among ADSM there was a significant association with having any thyroid disease diagnoses (HR = 1.48, 95%CI [1.15-1.89]). However, no significant relationship was found between COVID-19 infection and hypothyroidism (HR = 1.11, 95BoCI [0.93-1.31]), Hashimoto's thyroiditis (HR = 1.07, 95BoCI [0.77-1.48]), Grave's disease (HR = 1.20, 95BoCI [0.85-1.70]), or other thyroiditis (HR = 1.11, 95BoCI [0.83-1.47]). Non-ADSM adults from ages 18-64 showed significantly increased rates of hypothyroidism (HR = 1.11, 95BoCI [1.03-1.19]), Hashimoto's thyroiditis (HR = 1.15, 95BoCI [1.01-1.31]), Grave's disease (HR = 1.26, 95BoCI [1.09-1.46]), and other thyroiditis (HR = 1.31, 95BoCI [1.18-1.45]).

ADSMs with COVID-19 infection demonstrate an increased risk for combined thyroid disease, although non-ADSM adults had significantly increased rates of Grave's disease, Hashimoto's disease, hypothyroidism, and other thyroiditis. These results highlight that even in young, healthy populations like the ADSMs, COVID-19 can lead to long-term thyroid dysfunction.