Title: Tanzania national survey on iodine deficiency: impact after twelve years of salt iodation

Transcription

1 Reviewer's report Title: Tanzania national survey on iodine deficiency: impact after twelve years of salt iodation Version: 1 Date: 17 March 2009 Reviewer: Frits van der Haar Reviewer's report: Assey et al Tanzania national survey of iodine deficiency: Impact after twelve years of salt iodation Summary This manuscript should definitely be considered for publication. It reports about the results of a national survey aimed at taking stock of the progress made by a well-planned, multi-sector effort to eliminate iodine deficiency in Tanzania, a country with well-documented severe IDD in the past. Initiated by the Nutrition Unit in the Ministry of Health (later transformed to the Tanzania Food and Nutrition Center), a National Expert Committee in the late 1970s developed a wide-ranging plan with short-term and long-term components that have since then guided the activities to ameliorate IDD in the country. This same approach became folded at later stage into the global guidance recommended by WHO, ICCIDD and UNICEF as the basic framework for eliminating IDD in countries with a significant public health problem. The manuscript reports on the outcomes from a staged national tactic of targeted, high-dose iodine supplements in 27 most-affected districts during , which was gradually replaced by the national USI strategy. The present survey was conducted years after salt iodization was initiated satisfactorily. The manuscript demonstrates widespread improvement in household use of adequately iodated salt, overall near optimal urinary iodine excretion patterns and a highly significant reduction of the IDD burden in the population. There are some residual IDD problems and the current practices in salt industries are not optimal. The manuscript exposes these issues adequately and offers recommendations on the proper way forward. Overall comments: (a) Although the discussion paragraph draws on factors of Tanzania s salt production and supply system, it does not sufficiently exposes the complex salt industry situation: Tanzania has a multi-faceted salt sector, which is in constant flux and widely dispersed over the territory, has a high variation in scale and is incoherent in production technology. Also, a number of areas and/or population segments depend on import, periodically and/or structurally. The sector cannot

2 be easily organized for partnering in the national coalition; there is not a single, unified sector. The public officials and the public health community have taken somewhat long in effectively engaging with the varied salt suppliers. The difference in the degree that the enterprises have incorporated the USI strategy is a major explanation for the sizable variation in the observed I-salt coverage and IUC distribution, but it cannot explain all the differences across districts. The manuscript uses specific examples of the situation to explain selected contrasting findings, which remains rather unconvincing since it leaves seemingly similar other findings out of consideration. It would be better to put a summary description of the complex, multi-faceted salt sector in the introduction and then use selected contrasting findings as illustrative explanations of the unique national salt situation in the discussion. (b) It is to be expected that along with successful adoption of the USI strategy, there will be a shift toward higher values in the overall population s UIC distribution and that the number of districts showing improved median UICs will rise. If the additional iodine supply is large and sudden, there is risk of iodine-increased side-effects (esp. hypothyroidism) in chronic iodine-deficient members of the population. This occurrence of IIH is self-limiting and it abates after some time, making it one among the spectrum of iodine-deficiency disorders. In the case of Tanzania, the first part of the overall approach during provided high-dose iodine supplements in the most affected districts, which was then followed and gradually displaced by USI in the entire country. Surely, the amount of risk of excessive iodine consumption must have been far greater in those early years than after 12 years (1st section of the discussion). Yet, the current manuscript is putting quite heavy emphasis on the excessive consumption of iodine. Using the cut-off at 200µg/L as criterion for assessing the proportion of excessive iodine consumption is incorrect. It is recommended to rewrite the issue in terms of balancing the risks of high and low iodine intake. Looking forward, therefore, while addressing the remaining problems of low iodine supply in some districts, attention needs being given also to those situations where the supply of iodized salt is apparently too high: Temeke, etc. The current description gives the unnecessary impression of sounding an alarm. However, there is already a growing recognition that the previously set salt iodine content has been too high and efforts are ongoing to reduce them to a more reasonable level. Specific comments are as follows: 1. Introduction. The most recent update of global progress has been published in Food and Nutrition Bulletin 29(3); , Please use the correct numbers and replace reference No 4; 2. Subjects/methods. 2nd section on page 4. Reference No 14 is incorrect; Same section: Unclear sentence The RPIs in turn trained districts staff, etc ; page 5 upper section: Unclear sentence The inter-rating variations, etc Please revise both sentences; 3. Page 5, section on Goitre prevalence. The TGP was used for ranking districts as to severity of ID (iodine deficiency). Since the survey uses I-salt for assessing

3 iodine consumption, and UIC for ID status, it is recommended that the authors use TGP as indicator for IDD status (not ID status); 4. Page 6: The TFNC laboratory participated in the EQUIP program run by CDC, Atlanta. At the time of lab analyses, was the laboratory certified as a successful participant in this program? Please state so. 5. Data analysis. Please include a description of Eta effect calculation; 6. Results. Were the calculations of I-salt use and of goiter prevalence weighted? 7. The manuscript states slightly over optimal iodine nutrition for the country-wide results of UIC. The 95% CI ( ), however, includes the optimal range of µg/L. Is the statement justified? 8. Discussion. The manuscript states on page 9 that the three indicators are concordant overall, but it does not offer analysis or confirmation of this concordance. The results (Table 1) indeed suggest general agreement between the I-salt and the UIC data, but this is NOT the case for TGP for either districts or regions. In fact, for the analysis by district, the TGP relation appears inverse to what is expected, as shown in the following table: Number of regions Number of districts I-salt N TGP#5% N TGP#5% UIC#200 #90% 8 2 (25%) 12 5 (42%) 9 (75%) <90% 13 4 (31%) 9 2 (22%) 3 (33%) 9. Page 10 again states concordance with TGP. This needs corrected. Also, the statement that rapid tests for I-salt are useful should be attenuated by adding the fact that the kit cannot be used for detecting highly iodized salt, a fact that is relevant when the USI strategy is reaching success, as is the case in Tanzania nd section page 10: The Rukwa region is left out, which makes the overall argument less convincing. Moreover, the TGP in both Rukwa and Iringa was high. Recommend removing the section. 11. Page 11, the section on advocacy/social marketing. (Figure 2 does not show salt producing regions). More importantly, since the manuscript does not report any effort or result of the communications activities in Tanzania, the argument is weak. Recommend removing the section. 12. Page 12. The manuscript states that Tanzania still has pockets of moderate and severe ID. The results, however, show that no district the TGP or UIC has a red flag. It is thus recommended to remove the severe part in this statement, and also remove the language of non-endemic areas (next sentence). The results show that Tanzania has left the endemic/non-endemic stage behind, and the issue is now becoming one of ensuring balance of optimal iodine nutrition, rather than fight endemic problems. 13. Urinary iodine concentration (page 12). The major issue of the manuscript is in the interpretation of the UIC levels. Contrary to the rapid test kit, UIC can indeed detect excessive levels. However, the cut-off used by the authors is incorrect. The agreement in the WHO, ICCIDD, UNICEF guideline is that a

4 median level >300µg/L indicates excessive (while >200µg/L is above requirements). It is recommended that the manuscript revises the data analysis and uses the 300µg/L cut-off for calculating percentages and district summaries. 14. Page 13. Although excessive I-salt issues in Temeke, Ilemela and Kisarawa are mentioned, the discussion leaves out any comment on the reasons why the UIC was near 400µg/L in Hai and Simanjiro districts. Surely, Temeke and Kisarawe are exceptional (around 800µg/L) and the reasons for that need being addressed. But Ilemela is as deviant as Hai and Simanjoro. Leaving the latter two districts out weakens the overall argument. 15. Page 14, 2nd section. The manuscript has not offered evidence that excessive intakes are a bigger problem than severe deficiency (see note 13 above). Please revise. 16. Table 1. Some of the data are incorrect (percentages of TGP in districts such as Kilosa, Dodoma, etc.). Please add a column of >300µg/L for UIC by district. The total of the number of UICs is not 4,522 but 4,521 while the sum in Table 4 is 4,523. Please verify the reported numbers. General: The discussion reports a variety of very reasonable explanations for the seemingly contrasting results obtained in the survey. Rather than using the survey results to generate the argument, however, it is recommended that the manuscript simply states that much (though not all) of the seemingly contrasting findings can be explained by known imperfections in the salt supply situation. The remainder would likely be simply due to observation weaknesses: The fact is that both the rapid test kit and the palpation data are rather inaccurate (and quite unreliable as indicator at district level which is stated in the manuscript). Major compulsory revisions: Address the descriptions of excessive, revise the cut-off from 200 to 300µg/L Specific comments numbered 2, 8, 9, 13, 15, 16 Minor revisions: Specific comment 1, 4, 5, 11 Discretionary Include a summary of the national salt situation in the introduction and use it to illustrate explanations for exceptional findings Remaining specific comments Level of interest: An article of importance in its field Quality of written English: Acceptable Statistical review: Yes, and I have assessed the statistics in my report. Declaration of competing interests:

5 I declare that I have no competing interests