Context. Wastewater surveillance has emerged as a useful tool in the public health response to the COVID-19 pandemic.
Gap. While wastewater surveillance has been applied at various scales to monitor population-level COVID-19 dynamics, there is a need for quantitative metrics to interpret wastewater data in the context of public health trends.
Aim. To develop quantitative metrics that integrate wastewater surveillance data with clinical data streams in order to evaluate the public health response.
Methods. We collected 24-hour composite wastewater samples from March 2020 through May 2021 from a Massachusetts wastewater treatment plant and measured SARS-CoV-2 RNA concentrations using RT-qPCR. We demonstrate the utility of three new metrics to monitor changes in COVID-19 epidemiology: (1) the ratio between wastewater viral titers and clinical cases (WC ratio), (2) the time lag between wastewater and clinical reporting, and (3) a transfer function between the wastewater and clinical case curves.
Findings. The relationship between wastewater viral titers and new COVID-19 clinical cases and deaths varies over time. We find that the WC ratio increases after key events, providing insight into the balance between disease spread and public health response. We also find that wastewater data preceded clinically reported cases in the first wave of the pandemic but did not serve as a leading indicator in the second wave, likely due to increased testing capacity.
Utilization. The relationship between wastewater and clinical cases changes over time, which could be due to increasing testing capacity, and can thus be used to assess the public health response. The WC ratio, time lag, and transfer function we proposed could complement a framework for applying wastewater surveillance to manage the global COVID-19 pandemic and future pandemics.
