Assessing the Impact of Wastewater Treatment Plants on Environmental Levels of Antibiotic Resistance

This chapter presents an overview of the basic principles involved in designing studies or monitoring programs that seek to assess the impact of a wastewater treatment plant (WWTP) on measures of antibiotic resistant bacteria (ARB) or antibiotic resistance genes (ARG) in receiving environments. It draws on causal inference theory that was developed in the context of epidemiologic research, these principles are widely useful in observational science and share common themes that have emerged in the disciplines of ecology and environmental impact assessment. Collider stratification bias, also known as selection bias, is caused by conditioning on a common effect of either the exposure or one of its causes and the outcome or one of its causes. Designing studies that involve exposures and outcomes measured in the natural environment (e.g., rivers) have their own suite of challenges, related to the large number of variables and factors that can affect and distort the causal relationship of interest.