COVID-19 pandemic and thyroid diseases

Background: The COVID-19 pandemic has been associated with various autoimmune manifestations. Several studies have suggested a potential association between COVID-19 and thyroid diseases (TDs); however, findings remain inconclusive and are primarily based on relatively small studies. Population-level data examining the differential impact of the pandemic on specific thyroid conditions are scarce. Objective: To examine the incidence patterns of Hashimoto's Thyroiditis (HT), Graves' Disease (GD), and Subacute Thyroiditis (SAT) during the COVID-19 pandemic compared to the pre-pandemic period. Methods: We conducted a population-based retrospective cohort study using interrupted time series analysis of adults (≥16 years) in the Clalit Health Services southern district of Israel from January 2018 to December 2022. New cases of TDs were identified using either ICD-9 codes, laboratory results, medication dispensing data or a combination of them. Monthly disease-specific incidence rates were compared between pre-pandemic (January 2018-February 2020) and pandemic (March 2020-December 2022) periods, with adjustment for seasonal variations. Results: Among 4,765 incident TD cases identified, 3,731 (78.3%) had HT, 698 (14.6%) had GD, and 336 (7.1%) had SAT. The mean age was similar across groups (43-45 years) with consistent female predominance (77%). Interrupted time series analysis revealed a significant 30% increase in HT incidence during the pandemic period (IRR 1.30, 95% CI 1.04-1.64, p=0.023), which began prior to the national vaccination campaign. GD showed a non-significant upward trend suggestive of a possible increased incidence (IRR 1.66, 95% CI 0.99-2.79, p=0.054). Conversely, SAT demonstrated a significant 54% reduction in incidence (IRR 0.46, 95% CI 0.21-0.99, p=0.049). Conclusions: The COVID-19 pandemic was associated with a significant increase in HT incidence and an unexpected decrease in SAT. These findings highlight the heterogeneous impact of the pandemic on different TDs.