Measuring Environmental Exposure to Enteric Pathogens in Low-Income Settings: Review and Recommendations of an Interdisciplinary Working Group

Abstract

Infections with enteric pathogens impose a heavy disease burden, especially among young children in low-income countries. Recent findings from randomized controlled trials of water, sanitation, and hygiene interventions have raised questions about current methods for assessing environmental exposure to enteric pathogens. Approaches for estimating sources and doses of exposure suffer from a number of shortcomings, including reliance on imperfect indicators of fecal contamination instead of actual pathogens and estimating exposure indirectly from imprecise measurements of pathogens in the environment and human interaction therewith. These shortcomings limit the potential for effective surveillance of exposures, identification of important sources and modes of transmission, and evaluation of the effectiveness of interventions. In this review, we summarize current and emerging approaches used to characterize enteric pathogen hazards in different environmental media as well as human interaction with those media (external measures of exposure), and review methods that measure human infection with enteric pathogens as a proxy for past exposure (internal measures of exposure). We draw from lessons learned in other areas of environmental health to highlight how external and internal measures of exposure can be used to more comprehensively assess exposure. We conclude by recommending strategies for advancing enteric pathogen exposure assessments.

Towards transformative WASH: an integrated case study exploring environmental, sociocultural, economic and institutional risk factors contributing to infant enteric infections in rural tribal India

“…After recent trials failed to interrupt enough infection transmission pathways to improve child health outcomes, the marching orders set for the sector emphasised the need for a holistic understanding of all key pathways for contamination of the environment and infant exposure to faecal pathogens [ 28 ]. The role of anthropologists, psychologists and other professionals in interdisciplinary teams for the design and delivery of WASH programmes is increasingly recognised [ 64 ]. Further efforts towards integrated assessments of exposures and holistic approaches to solutions in complex settings are needed to achieve the synergistic SDGs.…”

Achieving Sustainable Development Goals in water and sanitation sectors in India

“…Water, sanitation and hygiene being interlinked, unhygienic conditions and unsafe sanitation practices have severe adverse health consequences often inadequately borne by women and children (Baker et al 2017;Dwivedi et al 2019;Gwenzi 2021). Human excreta contain several pathogens, and chronic exposure and contamination of such faecal pathogens have severe health consequences especially among children (Mills et al 2018;Goddard et al 2020). Groundwater contamination from domestic sewage and unscientific disposal of human excreta is of significant public health concern, in rural and periurban areas (Rajmohan 2020;Bindra et al 2021).…”

Impacts of an urban sanitation intervention on fecal indicators and the prevalence of human fecal contamination in Mozambique

“…5–12 Notably, combined interventions did not provide greater protection than their constituent interventions alone, suggesting that key sources of pathogens and pathways of exposure are inadequately addressed by conventional WASH strategies. 6,7,9,13–15…”

“…[5][6][7][8][9][10][11][12] Notably, combined interventions did not provide greater protection than their constituent interventions alone, suggesting that key sources of pathogens and pathways of exposure are inadequately addressed by conventional WASH strategies. 6,7,9,[13][14][15] Characterizing fecal contamination in potential exposure pathways may help explain why specific interventions do or do not improve health by identifying which pathways the intervention interrupts and which remain unaffected. Fecal contamination is typically assessed by measuring fecal indicator organisms, microbes abundant in feces used to infer the presence of fecal contamination and therefore the likely presence of enteric pathogens, which are challenging to measure directly due to their diversity and low environmental concentrations.…”