Thyrotoxicosis outbreak linked to consumption of minced beef and chorizo: Minas, Uruguay, 2003-2004

Thyrotoxicosis is produced by excessive quantities of thyroid hormone. Its most common causes involve inflammation of the thyroid gland. Much more rarely, thyrotoxicosis is due to exogenous intake of thyroid hormones or iodide compounds. Few outbreaks are documented. In 2003 to early 2004, doctors in Minas, Uruguay noted a sharp increase in the incidence of thyrotoxicosis in a neighbourhood, with multiple cases within families. The objective of this study was to identify the source of the outbreak.

A case-control study was conducted following surveillance and environmental inspection.

Case patients were symptomatic residents of Minas with documented thyroid-stimulating hormone concentrations <0.1 microUI/ml or <0.49 microUI/ml and elevated free triiodothyronine or free thyroxine. Control subjects were frequency matched with case patients by barrio of residence and age. Case patients, control subjects and persons who prepared and purchased household food were interviewed using a standard questionnaire. Odds ratios adjusted (AOR) for age and gender were calculated by logistic regression in SUDAAN to account for neighbourhood and family clustering.

Fifty-nine case patients aged 9-74 years (median 39 years) were identified. Of the 56 interviewed, 52% were women and 71% resided in one barrio. Case patients were more likely than control subjects to eat minced beef at least weekly and purchase it from Butcher A [AOR 6.1; 95% confidence interval (CI) 2.61-14.46], and were more likely to eat chorizo at least weekly and purchase it from Butcher B (AOR 11.6; 95% CI 1.30-102.27). One beef supplier selling meat cuts containing thyroid gland was identified.

The most likely cause of this outbreak of thyrotoxicosis was consumption of minced beef and chorizo contaminated with thyroid gland. Tight regulation and oversight of slaughter, processing, and sales of meat and meat products are imperative for prevention of future outbreaks.