Defining the lead time of wastewater-based epidemiology for COVID-19

TL;DR

This paper explores the concept of lead time in wastewater-based COVID-19 epidemiology, emphasizing that its meaning varies across different applications such as early warning, prevalence estimation, and burst detection.

Contribution

It clarifies that there is no single lead time for wastewater-based COVID-19 monitoring and highlights the importance of context-specific interpretation of wastewater signals.

Findings

The lead time varies depending on the application.

Correlation between wastewater data and case counts depends on context.

Different applications require different interpretations of wastewater signals.

Abstract

Individuals infected with SARS-CoV-2, the virus that causes COVID-19, may shed the virus in stool before developing symptoms, suggesting that measurements of SARS-CoV-2 concentrations in wastewater could be a "leading indicator" of COVID-19 prevalence. Multiple studies have corroborated the leading indicator concept by showing that the correlation between wastewater measurements and COVID-19 case counts is maximized when case counts are lagged. However, the meaning of "leading indicator" will depend on the specific application of wastewater-based epidemiology, and the correlation analysis is not relevant for all applications. In fact, the quantification of a leading indicator will depend on epidemiological, biological, and health systems factors. Thus, there is no single "lead time" for wastewater-based COVID-19 monitoring. To illustrate this complexity, we enumerate three different applications of wastewater-based epidemiology for COVID-19: a qualitative "early warning" system; an independent, quantitative estimate of disease prevalence; and a quantitative alert of bursts of disease incidence. The leading indicator concept has different definitions and utility in each application.