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 -

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