Could wastewater surveillance help track SARS-COV-2 community outbreaks?

By Dan Hutchins, M.PhilDec 15 2020

Since it was first detected in Wuhan, China, in December 2019, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative pathogen of coronavirus disease 2019 (COVID-19), has infected over 73.37 million people and taken the lives of over 1.63 million worldwide.

As 2020 draws to a close, various national regulatory bodies have given the go-ahead on the innovative new mRNA vaccine candidate developed by Pfizer and BioNTech – including the UK, Canada and the USA. In the UK, targeted vaccinations are already being administered to the elderly, the immunocompromised and frontline healthcare workers.

While these are promising signs, the crisis is far from over. The complex logistics, financials and compliance-based issues of promoting herd immunity by vaccination at the national, not least global, level are yet to be fully ironed out.  

In the meantime, understanding the manifold modes of SARS-CoV-2 transmission and gaining an accurate picture of its prevalence is essential in crafting informed and targeted measures that curb its spread via non-pharmaceutical interventions (NPIs). Several recent studies have explored the risks associated with wastewater contamination as well as the epidemiological utility of wastewater surveillance in assessing the pathogen's prevalence through evidence of viral shedding in wastewater samples.

This research cluster comes amid the discovery of SARS-COV-2 ribonucleic acid (RNA) – the virus’s genetic material – in wastewater samples. Understanding the risk factors associated with this dynamic of potential viral spread will be particularly pertinent in addressing transmission chains that may arise in many developing countries where sanitation practices can be less robust and where widescale vaccination, for economic reasons, remains a more distant prospect. However, using wastewater surveillance alongside other approaches, like seroprevalence testing, might help bolster epidemiological efforts worldwide to track breakouts in a given locale or community.

A team of US-based researchers from Stanford University, the University of Michigan, Monterey Bay Aquarium Research Institute and the University of San Francisco recently conducted an illuminating study that explores this method and its potential uses. In doing so, they have underscored the potential utility of wastewater surveillance in managing SARS-CoV-2 outbreaks.

Study: SARS-CoV-2 RNA in Wastewater Settled Solids Is Associated with COVID-19 Cases in a Large Urban Sewershed. Image Credit: Graphical Abstract / EST

The team’s findings have been published in the latest issue of the journal Environmental Science and Technology.

The study

When a person is recovering from COVID-19, they can shed SARS-CoV-2 for up to several weeks post-infection. This typically occurs from the nasal tract, but as many studies have observed, traces of viral shedding can also be found in stool samples from convalescent patients. Because most cases of COVID-19 are asymptomatic to mild, assessing the presence and concentration of SARS-CoV-2 RNA in wastewater presents a potentially valuable adjunct resource to seroprevalence testing, which uses blood samples to test for the presence of neutralizing antibodies.

The team examined influent and solid samples from two wastewater treatment facilities in urban regions of the US. They quantified the presence of SARS-CoV-2 RNA from these samples “to inform the preanalytical and analytical approaches” and to assess which type harbored more viral targets.

The study worked to identify a method that not only detects the virus in wastewater samples but also tracks whether the infection rates are trending up or down.

The researchers found the settled solid samples had higher concentrations and provided better detection of SARS-CoV-2 compared to the liquid versions.

These results confirmed our early thinking that targeting the solids in wastewater would lead to sensitive and reproducible measurements of COVID-19 in a community. This means that we can track upward trends when cases are still relatively low," said co-senior author Krista Wigginton, an associate professor in civil and environmental engineering from the University of Michigan, USA.

Conclusion

More research is needed, note the researchers, to better understand the limitations of wastewater testing and to elucidate what more can be gleaned from this approach. The virus's rate of decay in wastewater, the extent and timeline of viral RNA shedding when sick and varying operations of different wastewater plants all have the potential to impact results.

The team believes their findings support the potential utility of wastewater surveillance and believe their research presents a possible way for policy-makers and public health officials to identify new outbreaks, find hotspots, confirm the decrease of cases and inform interventions.

This work confirms that trends in concentrations of SARS-CoV-2 RNA in wastewater tracks with trends of new COVID-19 infections in the community. Wastewater data complements the data from clinical testing and may provide additional insight into COVID-19 infections within communities," said co-senior author Alexandria Boehm, professor of civil and environmental engineering at Stanford University, USA.

Given that many asymptomatic cases go undetected and thus untested via real-time polymerase chain reaction reverse transcription RT-PCR (i.e. swap testing for live infection) perhaps this method provides an effective supplementary approach to seroprevalence tracking of SARS-CoV-2’s breakouts and pathogen prevalence.