Do iodine water purification tablets provide an effective barrier against cryptosporidium parvum?

Authors: STARK, J - CORNELL UNIVERSITY; BOWMAN, D - CORNELL UNIVERSITY; LABARE, M - U.S. MILITARY ACADEMY; FOGARTY, E - CORNELL UNIVERSITY; LUCIO-FORSTER, A - CORNELL UNIVERSITY; BARBI, J - CORNELL UNIVERSITY; Jenkins, Michael; PAVLO, M - U.S. MILITARY ACADEMY; BUTKUS, M - U.S. MILITARY ACADEMY

Submitted to: Military Medicine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/25/2005
Publication Date: 10/25/2005
Citation: Stark, J.A., Bowman, D.D., Labare, M., Fogarty, E.A., Lucio-Forster, A., Barbi, J., Jenkins, M., Pavlo, M., Butkus, M.A. 2005. Do iodine water purification tablets provide an effective barrier against cryptosporidium parvum?. Military Medicine. 170:83-86.

Interpretive Summary: Today, American soldiers are still using iodine tablets to disinfect local water sources to obtain their supply. Many units find themselves still using iodine tablets as their only barrier of protection against a suite of unknown biological contaminants. However, the efficacy of iodine tablets against the protozoan parasite Cryptosporidium (crypto for short) has not been well studied. Crypto is most commonly transmitted by drinking water contaminated with infected feces, and can cause acute diarrhea. This study was designed to determine the dose of iodine that effectively kills crypto and reduces the number of infectious crypto by at least a hundred-fold. Mice were used as the measure of iodine's effectiveness, and the number of crypto that makes half of a 10 mouse litter sick was determined. Six concentrations of iodine, ranging from 1 to 1000 part per million, were prepared, and to each concentration a measured dose of crypto were added and allowed to incubate for 35 min. The crypto were extracted from the iodine preparations and diluted in water. Measured quantities of crypto from the iodine treatments were then fed to mouse pups; from the number of infected mice per litter the number of crypto that each iodine concentration killed was determined. Results of the study demonstrated that the normal dose (16 parts per million) originally recommended by the Army reduced the number of crypto by less than ten-fold; whereas, a concentration of 29 parts per million reduced the number by one hundred-fold. This information may affect the Army's water treatment strategy for the field.

Technical Abstract: United States Army Iodine Water Purification Tablets were tested to determine their efficacy against Cryptosporidium parvum ' a protozoan resistant to chemical disinfection. Purified oocysts were added to phosphate buffered water and were then treated with varying concentrations of iodine or treated with iodine tablets as per US Army protocol. Neonatal mouse pups were then each inoculated with 10,000 treated oocysts, and 1 week later scored as infected or uninfected. Using this methodology, iodine tablets were found to be inadequate at the current dose prescribed by Army doctrine against C. parvum. The Army doctrinal dose of 560 mg-min/L, calculated as 16 mg of I2/L and 35 minutes of contact time, showed less than 1 log inactivation. A dose of 29 mg of I2/L at the same contact time was required to achieve a 2 log inactivation.