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Chlorine Tablets

Chlorine tablets, often branded as Aquatabs, have an effervescent base composed of the chlorine-based active ingredient sodium dichloroisocyanurate. Chlorine tablets are a point-of-use water treatment product that is used to disinfect water. They are a simple to use, inexpensive, and effective method for households to disinfect their own water. As chlorine tablets are dissolved in water, free available chlorine is released, which disinfects and provides short-term residual protection for the water and prevents water-borne diseases. Each tablet that PSI currently distributes is able to treat 20 liters of water, and tablets typically come in strips of 10.

Unit of intervention1 tablet

Formula67 mg of sodium dichloroisocyanurate (NaDCC) per tablet

Target populationall ages

For information about how PSI is increasing access to chlorine tablets to improve health and save lives, visit our website at:
http://www.psi.org/health-area/water-sanitation/water-treatment/

Model Overview

PSI’s chlorine tablet impact model is based on the Lives Saved Tool (LiST). LiST is used to estimate the number of deaths averted with complete coverage of chlorine tablets in select countries, representing the projected impact of chlorine tablets. This number of deaths averted at the population level is translated to deaths averted per chlorine tablet, using parameters such as existing coverage of water treatment products, per capita usage of water per day, and liters of water treated per chlorine tablet. Once we have deaths averted per tablet, we apply data from the 2010 Global Burden of Disease study to estimate the corresponding number of DALYs averted.

Model Outputs (impact metrics)

Estimates of DALYs averted, deaths averted, CYPs provided, and unintended pregnancies averted represent the projected health impact of the intervention. It is projected because it has not been directly measured.

Examples based on distribution of chlorine tablets in Pakistan in 2015 Statement of modeled results, examples:

In 2015, an estimated 2 deaths and 105 DALYs would be averted if 1,000,000 chlorine tablets were distributed in Pakistan.

For more details about how PSI models the impact of chlorine tablets, see below.

Model Details

Step 1: Running a projection in the Lives Saved Tool (LiST)LiST is a multi-cause mortality model developed by Johns Hopkins Bloomberg School of Public Health that estimates the number of deaths averted (or lives saved) through the scale up of maternal and child health interventions.

PSI begins by running a projection in LiST for select countries. In this projection, access to treated water is increased from the current, country-specific baseline (taken from DHS surveys) to 100%. LiST then projects the number of deaths averted among children under five by this increased level of coverage.

Step 1 Output:
Number of additional deaths averted (or lives saved) among children under five if coverage of chlorine tablets increased from baseline to 100% in select countries

Step 2: Estimating deaths averted per per 67mg NaDCC chlorine tablet among children under five PSI uses the step 1 output (deaths averted at 100% coverage of chlorine tablets) to estimate the number of deaths averted by a single chlorine tablet. To do this, we divide the number of deaths averted at 100% coverage by the number of tablets needed to reach 100% coverage among children under five.

PSI estimates the number of chlorine tablets needed to reach 100% coverage using a number of parameters, including existing coverage of water treatment products, per capita usage of water per day, and liters of water treated per chlorine tablet. We also account for wastage of chlorine tablets in the supply chain, assumed to be 10%.

Step 2 Output:
Under five deaths averted coefficient for chlorine tablets

Step 3: Estimating DALYs averted per 67 mg NaDCC chlorine tablet among children under fiveA DALY (or disability adjusted life year) includes two components: years of life lost due to premature death (YLL) and years lived with disability (YLD). DALYs averted are in turn comprised of YLLs averted and YLDs averted or, put simply: death and disability that is prevented by PSI interventions.

To estimate YLLs averted per chlorine tablets among children under five, PSI first estimates the number of years of life lost per death among children under five due to diarrhea in select countries. This is equal to the life expectancy at the average age of death from diarrhea. Age specific life expectancy is taken from the 2010 Global Burden of Disease study. The number of years of life lost per diarrhea death is then multiplied by the number of deaths averted per tablet among children under five (under five deaths averted coefficient), calculated in step 2 above for a selected country. This gives us the YLLs averted per tablet.

To estimate YLDs averted per chlorine tablet among children under five, we use a YLD/YLL ratio, based on the 2010 Global Burden of Disease study. This ratio represents the relative number of years lived with disability for every year lost due to death from diarrhea. We apply this ratio to the number of YLLs averted per chlorine tablet to estimate the number of YLDs averted per tablet among children under five.

Finally, YLLs averted and YLDs averted are added together to estimate the number of DALYs averted per chlorine tablet among children under five.

Step 3 Output:
Under five DALYs averted coefficient

Step 4: Extrapolate deaths and DALYs averted among children under five to all agesChlorine tablets impact individuals of all ages. In order to estimate impact at the population level, we have to extrapolate deaths and DALYs averted among children under five to deaths and DALYs averted among all ages. This is done by using two new ratios, both of which are calculated using the 2010 Global Burden of Disease study:

Each ratio is applied to its respective impact coefficient (deaths or DALYs averted among children under five per chlorine tablet) to estimate the number of deaths and DALYs averted among all ages.

Step 4 Output:
Deaths averted coefficient (all ages)
DALYs averted coefficient (all ages)