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Objective To assess the effectiveness of prevention program on iodine deficiency disorders and iodine nutritional status of residents in Guangdong Province.Methods Probability proportionate to size sampling(PPS) was employed in surveillance of iodine deficiency disorders.Thirty counties(cities,districts) were selected in Guangdong Province.In each county(city,district) one township(street) was selected; in each township (street) one primary school was selected and in each primary school 40 children aged 8-10 were chosen to examine their thyroid and to collect salt samples at their home for determination of salt iodine.Out of the 40 children,12 children were chosen to collect urine samples for determination of urinary iodine.From the primary schools chosen,40 grade 5 students were selected for intelligence quotient(IQ) test.In the nearby of the primary schools,3 townships(towns,street) were selected and in each township(town,street) 5 pregnant and 5 lactating women were selected to collect their urine samples for determination of urinary iodine.Type-B ultrasonic was used in measuring the thyroid volume.The iodine content of urine samples was measured by the method of arsenic and cerium catalysis spectrophotometry.The iodine content of salt was determined quantitatively with the titration method.IQ was tested by Chinese combined Raven's test.According to geographical location and the implementation of iodized salt,the effects of iodized salt on iodine deficiency disorders were analyzed in the plains and the Pearl River Delta Coastal region with mild iodine deficiency(iodized salt implementation region,referred to as the plains and the PRD),historical iodine deficiency areas (iodized implementation region) and the eastern and the western coastal areas of Guangdong(areas with non-iodized salt problem,referred to as the eastern and the western Guangdong).Results A total of 1200 children aged 8 to 10 were examined by type-B ultrasonic test,and goiter rate was 3.5％ (42/1200).The differences of goiter rate between the plains and the PRD,the historical iodine deficiency areas and the eastern and the western Guangdong were statistically significant (x2 =6.6,P ＜ 0.05).The goiter rate (6.1％) in the eastern and the western Guangdong was significantly higher than that of the plains and the PRD and the historical iodine deficiency areas (3.3％,2.0％,x2 =5.6,7.1,all P ＜ 0.05).A total of 1200 salt samples were examined.The median and coefficient of variation of iodine in the salt were 31.0 mg/kg and 23.2％,respectively.Coverage of iodized salt was 97.5％(1170/1200) while 96.1％(1153/1200) of consumed iodized salt was qualified.The median urinary iodine of 1200 children aged 8-10 was 186.5 μg/L,and the differences of median urinary iodine between the plains and the PRD,the historical iodine deficiency areas and the eastern and the western Guangdong were statistically significant(x2 =5.9,P ＜ 0.05).The median urinary iodine of the eastern and the western Guangdong(162.4 μg/L) was significantly lower than that of the plains and the PRD(207.5 μg/L,x2 =8.7,P ＜ 0.01).The difference of median urinary iodine between the plains and the PRD,the historical iodine deficiency areas and the eastern and the western Guangdong was statistically significant(x2 =58.9,P＜ 0.01).The median urinary iodine of the eastern and the western Guangdong(109.6 μg/L) was significantly lower than that of the historical iodine deficiency areas and the plains and the PRD(152.9,155.2 μg/L,x2 =18.3,20.6,all P ＜ 0.05).The mean IQ of the 1208 grade 5 students was 102.8 ± 14.3.The IQ of the plains and the PRD(104.3 ± 13.9) and the historical iodine deficiency areas(102.7 ± 14.3) was significantly higher than that of the eastern and the western Guangdong(100.3 ± 14.7,t =3.8,2.1,P＜ 0.01 orP＜ 0.05).Conclusions The goal of iodine deficiency disorders elimination is achieved as scheduled in Guangdong Province.The health level of general population has been improved significantly.Iodine nutrition is in the appropriate range (100-199 μg/L) in general population but low in pregnant women.The selling of non-iodized salt in the eastern and the western Guangdong Province should be followed closely.