Making waves: Plausible lead time for wastewater based epidemiology as an early warning system for COVID-19.

Wastewater-based epidemiology (WBE) has emerged as a useful tool in the fight to track and contain COVID-19 spread within communities. One of the motives behind COVID-19 WBE efforts is the potential for 'early warning' of either the onset of disease in a new setting or changes in trends in communities where disease is endemic. Many initial reports of the early warning potential of WBE have relied upon retrospective sample analysis, and delays in WBE analysis and reporting should be considered when evaluating the early warning potential of WBE that enable public health action. Our purpose in this manuscript is to establish a framework to critique the potential of WBE to serve as an early warning system, with special attention to the onset of viral shedding and the differential between results reporting for WBE and clinical testing. While many uncertainties remain regarding both COVID-19 clinical presentation and technical factors influencing WBE results, our analysis suggests at most a modest lead time interval ranging from six days for clinical testing to four days for WBE during community-level wastewater surveillance where clinical testing is accessible on-demand with a rapid time to results. This potential lead time for WBE subsequently increases in settings with limited clinical testing capacity or utilization. Care should be taken when reporting 'early detection' of COVID-19 disease trends via WBE to consider underlying causes (e.g., clinical testing lag or delayed result reporting) to avoid misrepresenting WBE potential.