Assessing the impact of water handling practices and seasonality on the effectiveness of a drinking water intervention in Beira, Mozambique - PROJECT SUMMARY/ABSTRACT Diarrhea caused by enteric pathogens infections is a leading cause of morbidity and mortality for children in low- and middle-income settings. Upgrading drinking water infrastructure is a common strategy for reducing enteric pathogen infections, which are predominantly transmitted through environmental media and most of which lack effective vaccines. However, upgraded water systems alone may not be sufficient to reduce exposures to enteric pathogens due to the potential for the introduction of contamination from unhygienic household water handling practices, after water is collected from the source. Seasonal changes in water availability may also influence waterborne disease transmission pathways, creating another potential barrier to reducing enteric disease. Here I propose to assess the impact of water handling practices and seasonality on waterborne transmission of enteric pathogens. I will analyze data from household surveys and microbiological data from drinking water alongside enteropathogen infection data from an impact evaluation assessing acute and chronic health outcomes in children up to 12 months of age associated with an upgraded drinking water system in Beira, Mozambique. A key advantage to the data from the ongoing study is the availability of microbiological data on infections with specific enteric pathogens, which may provide a more accurate estimate of health burden compared to reported symptoms alone. In Specific Aim 1, I will assess the impact of water handling practices, including water storage, household water treatment, and use of alternate water sources, on enteric pathogen infections in 12-month-old children. In Specific Aim 2, I will assess if and how household water handling practices interfere with improvements to drinking water source infrastructure using a mediation analysis framework. Specific Aim 3 will then assess the role of seasonality on differences in enteric health outcomes and drinking water exposure pathways. Findings from this analysis will provide insight into how behavioral and seasonal factors impact the relationship between drinking water quality and enteric pathogen infections in a low- income, urban setting. Understanding these factors will allow for insight into drivers of enteric pathogen transmission and potential targets for addressing the high burden of enteric disease in settings with limited infrastructure and vaccine availability.