Abstract
In recent decades, quantitative microbial risk assessment (QMRA) has been widely used to assess exposure to fecal microbes and associated health risks. In this study, a multipathway exposure assessment model was developed to evaluate exposure to fecal microbes for children under 5 in highly contaminated urban environments. Children had contact with various environmental compartments. The contamination levels of these compartments were estimated from fecal indicator counts in the environmental samples. Structured observations of child behavior (including activities, locations, and time) were used to model behavioral sequences as a dynamic network. The exposure model combines behavior sequences with environmental contamination, using additional exposure factors when needed, to estimate the number of fecal microbes transferred from environmental sources to human oral ingestion. As fecal exposure in a highly contaminated urban environment consists of contributions from multiple pathways, it is imperative to study their relative importance. The model helps us better understand the characteristics of the exposure pathways that may be driven by variation in contamination and by variable behavior, like hygiene and high‐risk activities. Importantly, the model also allows prediction of the quantitative effects of an intervention—the expected reduction in exposure due to infrastructural or behavioral changes—by means of scenario studies. Based on experience with this exposure model, we make specific recommendations for additional studies of child behavior and exposure factors in order to fill critical information gaps and improve the model structure and assumptions.
Highlights
Exposure to fecal contamination has a negative impact on child health, growth, and development
The multipathway exposure assessment model was applied to data from four neighborhoods in Accra, Ghana, to assess the exposure to fecal contamination for children under 5 living in those neighborhoods
The present study introduces a new, interdisciplinary approach by integrating multipathway exposure assessments with social science methods (Ettema, Borgers, & Timmermans, 1995; Leszczyc & Timmermans, 2002) that provide a quantitative model of human behavior based on observational data
Summary
Exposure to fecal contamination has a negative impact on child health, growth, and development. A short-term effect of exposure to fecal pathogens is diarrheal disease, which is a leading cause of mortality and morbidity in children under 5 in low-income countries (World Health Organization, 2009). Long-term exposure to fecal contamination increases the risk of environmental enteric dysfunction, malnutrition, and stunting (Humphrey, 2009; Jiang, Tofail, Ma, Haque, Kirkpatrick, Nelson, & Petri, 2017; Mbuya & Humphrey, 2016). When children live in a highly contaminated environment, multiple sources contribute to exposure to fecal microbes simultaneously and dynamically. In 1958, the F-diagram was introduced by Wagner and Lanoix to explain multiple pathways and barriers for disease transmission (Wagner & Lanoix, 1958). This conceptual diagram illustrates how fecal microbes
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