Policy impact evaluation: A potential use case for longitudinal monitoring of viruses in wastewater at small geographic scales

We used wastewater monitoring data to evaluate the impact of public health policies and interventions on the spread of COVID-19 among a university population. We first evaluated the correlation between incident, reported COVID-19 cases and wastewater SARS-CoV-2 RNA concentrations and observed changes to the correlation over time. Using a difference-in-differences approach, we evaluated the association between university COVID-19 policy changes and levels of SARS-CoV-2 RNA concentrations in wastewater. Policy changes associated with a significant change in campus wastewater SARS-CoV-2 RNA concentrations included changes to face covering recommendations, indoor gathering bans, and routine surveillance testing requirements and availability. We did not observe changes in SARS-CoV-2 RNA concentrations associated with other policy changes. The work presented herein demonstrates how longitudinal wastewater monitoring of viruses may be used for causal inference such as policy impact evaluation, especially at small geographic scales.