Goiters in Peace Corps Volunteers from Water Purification Units

Abstract & Commentary

Synopsis: In January 1998, the Peace Corps contacted the CDC about an increase in goiter among Peace Corps Volunteers in Niger, West Africa. A survey was then undertaken of 96 PCVs to assess thyroid status and practices related to iodine intake.

Source: Khan LK, et al. Thyroid abnormalities related to iodine excess from water purification units. Lancet 1998; 352:1519.

Forty-four peace corps volunteers (pcvs) (46%) had enlarged thyroid glands, of whom 30 had normal thyroid function tests. Thirty-three volunteers had thyroid dysfunction; 29 had serum TSH (thyrotropin) levels of 4.2 m U/L or greater (nL 0.4-4.2) and four had suppressed TSH levels (£ 0.4). Mean urinary iodine concentration showed excessive iodine exposure in volunteers.

There was no evidence of a high concentration of iodine in diet, salt, medications, or nutritional supplements, nor was there geographic clustering of goiters. Distribution of a two-stage water purification system consisting of two ceramic filters with an iodine-resin second stage to inactivate bacteria and viruses had been initiated beginning in 1995 and was temporally related to the incidence curve of thyroid abnormalities among these volunteers. The adjusted odds ratio for a TSH abnormality adjusted for age, sex, and confounding factors was 3.9 (95%; CI 1.1-14.3) for two-stage water filters with a positive relationship to duration of exposure (adjusted odds ratios, 4.6 and 10.9 at 6 and 12 months, respectively). Because of this strong association, all iodine-based filters for PCVs in Niger have been replaced with microfiltration, chlorine purification, or boiling, and thyroid abnormalities are continuing to be monitored.

Comment by Michele Barry, MD

This is a fascinating report with far reaching public health ramifications for long-term travelers using water purification units with iodine-containing resins. Because of the arid environment in Niger, most PCVs reported consuming 5-9 L of water each day, which led to an intake of approximately 50 mg iodide per day through drinking water—at least 330 times the recommended dietary allowance of 0.15 mg. Clearly, more studies are needed to provide additional data on the natural history and reversibility of chronic exposure to high concentrations of iodine. The iodine content of water from newer three-stage water purification systems that use a carbon-based third stage to remove residual iodine should be tested to clearly determine the limits of protection using such a three-stage system.

At present, travel medicine specialists must caution long-term travelers, especially pregnant women and patients with a history of thyroid disease, that significant iodine exposure can occur with long-term use of certain water purification units. The risks of excessive iodine intake during pregnancy should be clearly emphasized for women who are either pregnant or plan pregnancies while on long-term assignments abroad requiring prolonged use of water purification equipment.1 The Recommended Daily Allowance of iodine during pregnancy is 175 mcg/d. The fetal thyroid is sensitive to excess iodide and goitrous hypothyroidism in the fetus may result from such intake (Wolff-Chaikoff effect). The 50,000 mcg per day iodine intake that occurred in these volunteers would cause these additional problems for women who are pregnant.

Reference

1. Samuel B, Barry M. The pregnant traveler. Infect Dis Clinics North Am 1998;12:325-354.