Buddhachinaraj Hospital and Wang Thong Hospital reported that the 25 prisoners transferred to the hospitals, due to limb numbness and tachycardia, all had low potassium in their blood.

Earlier, two of the four inmates were said to have died from heart failure with the other two from coronary artery disease.

Pol Col Naras said he believed that the environment and food sanitation at the prison were up to safety standards, adding that personnel from Phitsanulok Provincial Public Health Office are screening prisoners for signs of toxic goiter.