Discussion

An elastomer system for the controlled release of iodine was designed to provide deficient populations with a physiological quantity of iodine via a universal vehicle : water. The silicone elastomer was an appropriate choice given its properties with regard to the programmed diffusion of molecules such as those of Nal, the absence of toxicity of this type of material, and its stability even under severe storage and transport conditions. The system is particularly suitable for use under realistic conditions in a tropical environment (adaptation to well flow rate, stable diffusion over more than 1 year, know-how for controlled release system installation in boreholes). In the field, the presentation of the device to the study village populations elicited considerable interest. In these highly deficient populations, goiter is considered an everyday public health problem. Installation of the system posed no major technical problems and was effected with th villagers? assistance.

From the first week to study termination, borehole water iodine levels remained stable over time irrespective of season. In the test well, the levels were slightiy higher than predicted because the flow rate had been overestimated at <600 L/h. Nonetheless, iodine intake remained within physiological limits. lt must be emphasized that toxic levels of iodine require very high intakes (200 to 500 mg per kilogram of body weight per day) ; long-term intakes of less than 1 to 2 mg per day are considered nonhazardous in humans.12

From a methodological viewpomt, it may seem that subject selection would ideally have consisted in recruitment of a cohort of predefined subjects. However, in Africa, an individual?s presence in the village depends on subsistence imperatives (agriculture, hunting) that are linked, in particular, to season. It was therefore considered more realistic to randomly select, for each time point, the number of test subjects required. Although this method would increase the intrinsic variance of the results it would prevent the risk of an excessively high number of subjects being lost to follow up.

The urinary iodine results reflect the excellent compliance of the population. The possibility that the population might reject the intrusion of the system into their nutritional environment was easily overcome by the investigators? educative and informative roles. The persistence of effective iodine intake even after a year of use under realistic tropical conditions was demonstrated by the urinary iodine levels determined, for the test village, in successive assays.

The relative stability of GIa goiter frequency may be explained by the gradual shift of more severe forms toward the left, as shown in Figure 3. The decrease in goiter frequency was significant at 1 year. As of month 6, once thyroid iodine stores had been replenisbed, urinary iodine levels showed that iodine defidency had been eradicated from the village. The decrease in goiters appeared regular over time.

The device appears to be appropriate for most iodine-deficient zones in view of its clinical efficacy and the stability and duration of iodine release. lt may be positioned in any water source, whether still or flowing. In the case of boreholes, its installation can coincide with the annual maintenance recommended by almost all manufacturers.

For a year, the controlled release system supplies a physiological supplement of iodine that is beneficial for all subjects, whatever their age, sex, nutritional status, or previous medical status, while having no ecological effects. In addition, its large-scale feasibility is not impeded by any of the obstacles that applied to previous methods for combating iodine deficiency. The system provides collectives prophylaxis and requires no medical intervention, mobilization, or immobilization of populations.