and objects or utensils of frequent use, thus reducing the chances of person-to-person transmission and food or water contamination. The variety of transmission channels has been summarized in the seminal “F-diagram” reproduced in Figure 3.

High levels of enteric pathogens manifest in three main ways that adversely affect nutritional outcomes, especially for young children: diarrheal diseases, gastrointestinal infections and intestinal parasitic infections (soil helminthes and protozoans).<sup>11</sup> The pathogens that cause diarrheal diseases are transmitted mainly via fecal-oral routes, by ingestion of contaminated food, water, or other beverages, by direct or indirect contact with contaminated hands, animal or human feces.<sup>12</sup> Gastrointestinal infections and environmental enteropathy, are caused by ingestion of fecal bacteria in large quantities. Intestinal parasitic infections such as ascariasis, trichuriasis and hookworm are transmitted through soil contaminated with feces; giardia is a waterborne infection but can also be transmitted through food and person-to-person contact.

Despite being less visible than diarrheal diseases, subclinical gastrointestinal infections and intestinal parasitic infections also affect nutrition in substantial ways. The absorption of nutrients is reduced by direct loss through diarrhea, especially by repeated episodes, but also by continuous and silent theft of nutrients by parasites (including blood by hookworm), and by diversion of energy and proteins to combat infections.<sup>13</sup> Environmental enteropathy reduces absorptive capacity while increasing permeability of the small intestine (Humphrey, 2009). The result is faltering weight and height for age and increased risk of anemia.<sup>14</sup> It is commonly believed, on the basis of practitioners’ claims and some observational studies, that water, sanitation and hygiene investments may result in additional benefits when provided together. Arnold _et al._ (2013) note that, even though some observational studies and theoretical modeling of transmission pathways support the use of combined approaches promoted by implementing agencies, rigorous evidence justifying this approach is scarce. A meta-analysis by Fewtrell _et al_ . (2005) finds that the only evidence on combined interventions do not reduce diarrhea more than individual interventions. Our study, being the first large randomized trial exploring gains from sanitation promotion and handwashing implemented separately and in combination, provides important evidence for understanding the potential complementarities of WASH provision for at-scale interventions.<sup>15</sup>

> 11 Other important tropical diseases that can be prevented through adequate water, sanitation and hygiene include trachoma and schistosomiasis.  [Mara, 2010]

> 12 See Clasen _et al_ . (2010), Prüss _et al_ . (2008)

> 13 Chambers ,R (2012) Handout on fecally-transmitted infectious and undernutrition.

> 14 Helminth infections are also frequent cause of anemia in pregnant women [Mara, 2010]

> 15 In the near future, it is expected that other ongoing trials like the WASH benefits study will contribute to a more comprehensive understanding of the interactions among water quality, sanitation, handwashing, and nutrition interventions alone and combined designed as an efficacy trial for proof of concept.  See Arnold _et. al_ (2013) for the complete study protocol.

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