No causal relationship between Yersinia enterocolitica infection and autoimmune thyroid disease: evidence from a prospective study.

The objective of this study was to evaluate prospectively the relationship between Yersinia enterocolitica (YE) infection and the development of overt autoimmune hypo- or hyperthyroidism (study A) and the de novo occurrence of thyroid antibodies (study B). This was a prospective cohort study of 790 euthyroid women who were first- or second-degree relatives of autoimmune thyroid disease (AITD) patients. Follow-up was 5 years, with annual assessments. Study A was a nested case-control study in which YE serological status was measured between cases {subjects who developed overt hypothyroidism [thyroid stimulating hormone (TSH) > 5·7 mU/l and free T4 (FT4) < 9·3 pmol/l] or overt hyperthyroidism (TSH < 0·4 mU/l and FT4 > 20·1 pmol/l)} and matched controls. For study B, 388 euthyroid women without thyroid antibodies at baseline were enrolled. The YE serological status was compared between subjects who developed thyroid peroxidase (TPO)-antibodies and/or thyroglobulin (Tg)-antibodies at 4-year follow-up and those who remained negative. For study A, the proportion of subjects positive for Yersinia enterocolitica outer membrane protein (YOP) immunoglobulin (Ig)G or YOP IgA did not differ between cases and controls at baseline. One year before the development of overt hypo- or hyperthyroidism, the proportion of subjects with YOP IgG was not different between cases and controls, but YOP IgA were less prevalent in cases. For study B, de novo occurrence of TPO (or TPO-antibodies and/or Tg-antibodies) did not differ between subjects in whom YOP IgG were positive or negative at baseline. Neither persistence nor emergence of YOP IgG at 4-year follow-up was associated with the occurrence of TPO-antibodies or Tg-antibodies. Similar results were observed with respect to YOP IgA. YE infection does not contribute to an increased risk of thyroid autoimmunity.