This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nutrition and health, Subject name: Social & Preventive Medicine
As per the World Health Organisation guidelines, iodine deficiency disorders are endemic in a community if the prevalence of goiter in school age children in more than - 
Select and explain. 
A. 1%, B. 5%, C. 10%, D. 15%
C: 10%
Answer: C: 10% 
Explanation: Epidemiological criteria for assessing severity of IDD. Total goitre Rate (TGR) : Grade I + Grade II Median urinary iodine excretion. Thyroid volume (Ultrasound). Salt iodine content Criteria for sustainable elimination of IDD. Median Urinary Iodine Excretion 100 mcg/L Level of iodization: 1) 30ppm at production level 2) 15 ppm at consumer level Total goitre Rate (TGR) :<5% Ref: Assessment of IDD and monitoring their elimination, WHO 3rd edition