Control of iodine-deficiency disorders following universal salt iodization in Shenzhen, China, 1997-2011

Background. Since universal salt iodization (USI) was implemented in Shenzhen, China, in 1996, evaluation of the time trend of USI to indicate the control of iodine-deficiency disorders has not been performed. Objective. To assess the time trend of median urinary iodine and total goiter rates from 1997 to 2011. Methods, Probability-proportionate-to-size sampling was employed in the surveillance of iodine-deficiency disorders, for which schoolchildren aged 8 to 10 years were randomly selected from five districts of the city during each iodine-deficiency disorders survey. Urinary iodine content and thyroid size were measured by ammonium persulfate oxidation and B ultrasound, respectively. Results. The coverage of iodized salt increased from 73.2% in 1997 to more than 90% in 2011. The median urinary iodine of children aged 8 to 10 years varied between 207.1 and 278.8 mu g/L; these levels were above the urinary iodine level in 1995. The proportion of urine samples with iodine content above 300 mu g/L was 45.6% in 1997 and decreased to 20.8% in 2011, indicating excessive consumption of iodine by the children. The goiter rate among children dropped from 10.8% in 1997 to 1.3% in 2011; both values were lower than the goiter rate in 1995, indicating that the spread of endemic goiter was under control. Conclusions. Preliminary elimination of iodine-deficiency disorders was achieved by USI in Shenzhen. Nevertheless, some problems still existed, such as over-iodization. To clarify the causes of excessive urinary iodine content, the various sources of iodine from the diet need to be investigated in the future.