EFFICACY OF IODINE WATER-PURIFICATION TABLETS AGAINST CRYPTOSPORIDIUMOOCYSTS AND GIARDIA CYSTS

The ability to control water-borne diseases is critical for soldiers, hikers, and others who may need to drink directly from an outdoor sour ce. Water-borne protozoan parasites that are specifically of concern a re Giardia and Cryptosporidium because of their resistance to halogen disinfection. The purpose of this study was to determine the effective ness of iodine tablets against Giardia and Cryptosporidium under gener al-and worst-case water conditions that might be found in the field. G iardia cysts and Cryptosporidium oocysts were exposed to iodine accord ing to manufacturer's instructions (two tablets/L = 13-18 mg/L for 20 minutes). This dose inactivated 3-log(10) of Giardia in general-case w ater and pH 9. In worst-case water, however, only about 35% of cysts w ere inactivated at pH 5. Fifty minutes were required to achieve a 3-lo g(10) reduction at pH 5. Cryptosporidium oocysts were more difficult t o inactivate. Only 10% were inactivated after a 20-minute exposure to iodine according to manufacturer's instructions; even after 240 minute s of exposure to iodine only 66-81% oocysts were inactivated. These da ta strongly suggest that iodine disinfection is not effective in inact ivating Cryptosporidium oocysts in water. Because this organism is com mon in all surface waters, it is recommended that another method of tr eatment be used before ingestion.