There has been some recent attention surrounding the potential to use molecular (i.e., RNA) detections of SARS-CoV-2 (the causative agent of COVID-19) in wastewater to track community prevalence. This approach, often termed Wastewater Based Epidemiology (WBE), has some potential advantages to case-by-case tracking, including improved throughput at the community level and tracking asymptomatic cases. It is critical to note that these detections do not represent culturable virus in the wastewater that would be necessary to cause infection; separate research is being conducted to assess the presence, persistence, and disinfection of SARS-CoV-2 in wastewater.
A recent paper led by Warish Ahmed at CSIRO and Jochen Mueller at the University of Queensland, and also including members of our research team at the University of Notre Dame, has demonstrated this as a proof of concept – First confirmed detection of SARS-CoV-2 in untreated wastewater in Australia: A proof of concept for the wastewater surveillance of COVID-19 in the community. Other recents studies in this vein has been published as preprints (e.g., Medema et al., Wu et al., Wurtzer et al.).
Ahmed et al. detected SARS-CoV-2 in two separate wastewater samples using two separate concentration methods, and detections were confirmed by sequencing. The number of infected individuals in the catchment area was also estimated using available virus shedding data and estimated per capita flowrates, and these values were within the same order of magnitude as clinical observations.
The study by Ahmed et al. and others supports the feasibility of WBE for tracking COVID-19 at the community level; however, critical questions remain to make these detections quantitative and predictive. One obvious area for future improvements includes methods for SARS-CoV-2 RNA concentration from wastewater. Nearly all reported SARS-CoV-2 RNA concentrations in wastewater have been low – this makes detection difficult. Specific areas to optimize the experimental methodology include viral RNA concentration and extraction, sample collection methods, and which molecular assays are used. In addition to improved methods, characterizing the efficiency of these approaches is necessary to refine prevalence estimates. For example, if the RNA concentration methods are 10% efficient, this would increase community prevalence estimates ten fold. Beyond method improvements, the current greatest source of uncertainty is the fecal shedding rate of SARS-CoV-2. Available data suggests these values vary by greater than five orders of magnitude both temporally and between cases – this results in model uncertainty greater than all other factors!
There is clearly significant research interest in developing WBE for SARS-CoV-2 monitoring. I hope that these early positive developments encourage continued development and research support of this promising area, both for COVID-19 and future infectious disease outbreaks.