A Cluster of Thyrotoxicosis, Presenting with Muscle Weakness, at a Prison in Sakon Nakhon Province, Thailand, 2019

In April 2019, a cluster of prisoners with muscle weakness and palpitation was detected at Prison A in Sakon Nakhon Province, Thailand. An investigation was conducted to describe epidemiological characteristics, and to provide appropriate control measures. A descriptive cross-sectional study was done. Suspected cases were prisoners or prison officers who had at least one of the following manifestations: muscle weakness, palpitation, fatigue, increased perspiration, weight loss, or tachycardia during 1 Jan to 30 Sep 2019. Confirmed cases were suspected cases who had low thyroid-stimulating hormone (TSH) levels. We interviewed food suppliers and examined the food ingredients. Food samples were collected to test for thyroid hormone. Thirty confirmed cases and 61 suspected cases were found. The overall attack rate was 4.6%. Only male prisoners were affected. The majority of the cases had low TSH and low serum potassium levels. All cases had a history of eating pork offals. Pork offal was suspected as the cause of elevated tri-iodothyronine (T3) and levothyroxine (T4) levels. Establishing standard of food quality for food supplier and evaluation of food material could prevent future outbreaks.