hygiene, and water supply for more than 20 million rural Bangladeshis; a matched cohort study in 100 villages found modest improvements in implementation and behavioral outcomes, but no impact on child diarrhea after 2 years of intervention [49]. Arnold _et al._ [50] documented large improvements in toilet coverage, smaller improvements in open defecation, no improvements in diarrheal disease or height-for-age Z-scores in a matched cohort study of combined sanitation, water, and hygiene interventions in Tamil Nadu, India (a pilot implementation of TSC). A similar percentage of households with toilets reported adult daily OD in the Tamil Nadu study (39%) as in this study (41%), despite implementation being complete for more than 23 months in most intervention villages in Tamil Nadu. The toilet coverage and open defecation levels in the Tamil Nadu study were similar to those we observed in Madhya Pradesh, however diarrhea prevalence was much lower in Tamil Nadu (1.8%) and the authors inferred that open defecation was unlikely to be an important source of diarrheal pathogen transmission for children during their study. Although the findings from the present study are consistent with the hypothesis that open defecation may not be important source of diarrheal pathogen transmission for young children, we did not collect extensive information to confirm or rule out all transmission pathways.

We would expect the TSC program to reduce child exposure to fecal pathogens through two main environmentally mediated pathways (Figure 1): (i) reduced open defecation of sick adults and older siblings or other children in the household compounds where young children may encounter feces, and (ii) reduced contamination of village drinking water supplies by fecal transport through the environment. Intervention households were more likely to report hygienic methods of child feces disposal than control villages (27% v. 18%), but there was no difference in the absence of human or animal feces observed during household visits (40% in both groups) and we did not observe lower prevalence of _Ascaris_ infections (Table 7). This suggests that the program did not successfully reduce pathogen transmission to children through soil. However, lower levels of _E. coli_ in drinking water and lower _Giardia_ prevalence in intervention villages compared to control villages provides some objective evidence to suggest that the TSC program may have reduced waterborne pathogen transmission. In the study population, 43% of households used bore wells that draw water from shallow groundwater aquifers that could be contaminated with feces, and 33% used piped water that can be cross-contaminated with sewage and run off due to negative pressure in the pipes during non-supply hours. _Giardia_ may have proven to be a more sensitive measure of child health impact compared to diarrhea because it was more prevalent in this study population (Table 7) and it is more specific to a transmission pathway the intervention is thought to block (waterborne transmission). These findings certainly merit future research, but we recommend caution in over-interpreting the result by itself because it was the only measure of health improvement among many measured in this study.

The majority of intervention studies in the water, sanitation, and hygiene sector have used caregiver reported diarrhea as their primary outcome [41], which theoretically could be subject to differential, biased reporting in unblinded trials [27,28]. We included numerous objective child 20 / 41