Introduction of the Personal Domain in Water Sanitation and Hygiene (WASH), a New Approach to Identify Missing Health Impacts.

The water sanitation and hygiene (WASH) sector has provided beneficiaries in low and middle-income countries with latrines and clean water for decades. However, we still need good evidence documenting the expected health impact. This paper investigates why we lack this evidence and ways to move forward. Using mTEC agar, we monitored E. coli contamination on selected "hotspot" surfaces within the kitchen environments of 32 low-income households in Dhaka, Bangladesh, every six weeks for two years. Despite being washed, the highest average contamination was found on food plates, at 253 cfu/10 cm 2 , followed by cutting knives, with 240 cfu/10 cm 2 . The drinking vessel surfaces and the latrine doorknobs had the lowest contaminations, with E. coli means of 167 and 73 cfu/10 cm 2 , respectively. These findings imply a need to measure an individual's pathogen exposure as close to the mouth as possible to estimate the true pathogen exposure. The paper proposes introducing the new "personal domain"-the point of consumption-as the physical sphere in which WASH interventions should be assessed. With this approach, we can observe and quantify the different pathogen exposure routes and, with this, further improve WASH interventions.