Infection by Cag A Positive Strains of Helicobacter pylori is Associated with Autoimmune Thyroid Disease in Iranian Patients

Background: Infectious agents have been suspected as a triggering factor for development of autoimmune thyroid disease (ATD). Some reports from Western countries have suggested association between Helicobacter pylori (HP) infection and ATD. Objective: To investigate the association of ATD with Cag A seropositivity in a population with high rate and early age of onset of HP infection. Methods: IgG anti HP and anti Cag A antibodies were measured in 88 patients with ATD and compared with results of 112 healthy individuals. Results: The rate of infection with HP was not significantly different in patient and control groups, but there was significant association between ATD and infection with Cag A strains (p<0.005). This association was significant for both hypothyroidism (p<0.005) and Graves' disease (p<0.02). Cag A antibody level correlated with titers of thyroid auto antibodies (p<0.001). Conclusion: In a population with high rate and early age of onset of HP infection, only infection with Cag A positive strains is associated with ATD, and this may be due to immune cross reactivity.