In 1984, an outbreak of thyrotoxicosis was observed among residents of southwestern Minnesota and the surrounding areas of South Dakota and Iowa. The source of the affliction, dubbed “hamburger thyrotoxicosis,” was traced back to the consumption of ground beef prepared from gullet trimmings processed by a single slaughtering plant. This was later confirmed by findings of bovine thyroid tissue in the trimmings as well as the observation of sudden increases in serum thyroid hormone concentrations in volunteers who ate the ground beef from this plant. The thyroid gland tissue of cattle produces T3 and T4, known as thyroxine and triiodothyronine respectively, which are also relatively heat-stable so that after being ground into hamburger by gullet trimming, these hormones also survived cooking. After consumption, these thyroid hormones are absorbed through the small intestine, enter the circulation and are biologically active. The hormone excess in the body’s bloodstream leads to clinical signs of hyperthyroidism such as nervousness, sleeplessness, weight loss, and fatigue. The USDA later banned the practice of gullet trimming for human food consumption in 1986. Interestingly, gullet trimming is not banned for pet food and the same condition, caused by consuming thyroid tissue, can arise in animals. This outbreak highlighted how butchering practices can have major health consequences, leading to stricter food safety standards to protect consumers.
Mike Osterholm, CIDRAP Director, discusses how the outbreak was solved in his Inspired to Heal episode Outbreak Investigations: Toxic Burgers and Toxic Shock.