Measurement in the study of human exposure to animal feces: A systematic review and audit.

Background: Human exposure to animal feces is increasingly recognized as an important transmission route of enteric pathogens. Yet, there are no consistent or standardized approaches to measurement of this exposure, limiting assessment of the human health effects and scope of the issue.
Objective: To inform and improve approaches to the measurement of human exposure to animal feces, we audited existing measurement in low- and middle-income countries.
Methods: We systematically searched peer-reviewed and gray literature databases for studies with quantitative measures of human exposure to animal feces and we classified measures in two ways. First, using a novel conceptual model, we categorized measures into three 'Exposure Components' identified a priori (i.e., Animal, Environmental, Human Behavioral); one additional Component (Evidence of Exposure) inductively emerged. Second, using the exposure science conceptual framework, we determined where measures fell along the source-to-outcome continuum.
Results: We identified 1,428 measures across 184 included studies. Although studies overwhelmingly included more than one single-item measure, the majority only captured one Exposure Component. For example, many studies used several single-item measures to capture the same attribute for different animals, all of which were classified as the same Component. Most measures captured information about the source (e.g. animal presence) and contaminant (e.g. animal-sourced pathogens), which are most distal from exposure on the source-to-outcome continuum.
Discussion: We found that measurement of human exposure to animal feces is diverse and largely distal from exposure. To facilitate better assessment of the human health effects of exposure and scope of the issue, rigorous and consistent measures are needed. We recommend a list of key factors from the Animal, Environmental, and Human Behavioral Exposure Components to measure. We also propose using the exposure science conceptual framework to identify proximal measurement approaches.
Competing Interests: Declaration of competing interest The authors declare they have nothing to disclose.
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