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Wastewater, COVID-19's Canary in a Coal Mine

Published on: 09-Nov-2020


Assoc Prof Janelle Thompson, Principal Investigator at the Asian School of the Environment and the Singapore Centre for Environmental Life Sciences Engineering

For the last several months, Associate Professor Janelle Thompson, a Principal Investigator at the Asian School of the Environment (ASE) and the Singapore Centre for Environmental Life Sciences Engineering (SCELSE), has been leading a team of scientists in conducting a comprehensive survey of wastewater surveillance approaches to aid in COVID-19 epidemiology.

The survey is laid out in a paper published in the October issue of Water Research, titled Making waves: Wastewater surveillance of SARS-CoV-2 for population-based health management. The paper is the product of a multi-national collaboration of NTU faculty with colleagues at universities in Argentina, Spain, India, and the USA, together with local colleagues from the Singapore-MIT Alliance for Research and Technology, and the National Environmental Agency (NEA). In addition to Assoc Prof Thompson, the NTU faculty on the team includes Associate Professor Ng Lee Ching, from the School of Biological Sciences (SBS), who is also Director of the NEA’s Environmental Health Institute, Assistant Professor Monamie Haines of the School of Social Sciences (SSS) and Professor Stefan Wuertz of the School of Civil and Environmental Engineering (CEE) who is also Deputy Centre Director (Education & Training) and Research Director (Environmental Engineering) of SCELSE.

With such a plethora of multi-disciplinary perspectives behind it, the paper makes a substantive case for prioritising the monitoring of wastewater as a means of augmenting ongoing efforts in the testing and tracking of individual COVID-19 cases.

Thus far, Singapore has employed an aggressive testing regime alongside extensive contact tracing as part of its strategy to contain the spread of COVID-19 in Singapore.

However, such methods are not infallible – with no noticeable symptoms, asymptomatic disease carriers have little reason to be tested, and instead go about their daily lives while continuing to spread the disease.

This is where wastewater surveillance comes in, as Assoc Prof Thompson and co-authors propose in the paper.

To begin with, wastewater samples are collected “downstream”, from sewage water treatment plants, as well as “upstream”, from maintenance holes at the neighbourhood level. These samples are then processed to detect the presence of viral RNA of SARS-CoV-2, the disease-causing agent behind COVID-19.


Because asymptomatic and mildly symptomatic cases are under-reported, clinical data that is used in tracking COVID-19 is limited in its accuracy.

Wastewater surveillance, in contrast, can occur in real-time and provide a comprehensive cross-section of COVID-19 presence in the community, including asymptomatic carriers who test negative for nasopharyngeal swab tests.

It is also a relatively simple solution, being both cheap and scalable in large and small populations – as the remnants of SARS-CoV-2 viral RNA shed in stool samples last for a longer time than in the respiratory tract.

But most importantly, wastewater surveillance can serve as an early-warning system for an impending outbreak – much like a canary in a coal mine. If estimated cases based on wastewater surveillance significantly outnumber the actual number of recorded cases, it becomes possible that there are “undiscovered” clusters in the community.

This information is essential for policy makers in charge of public health – with wastewater surveillance helping clinical data to paint a more precise picture of the true prevalence of COVID-19 in a neighbourhood, decisions about tightening or loosening safety measures can be more accurately made.

Furthermore, as the paper points out, there are also other important reasons to employ wastewater surveillance.

For one thing, RNA viruses like SARS-CoV-2 have high rates of mutation, a trait that works to the virus’s advantage as it evolves to be less susceptible to emerging treatments. Epidemiological approaches that integrate wastewater surveillance data can help mitigate this by tracking the emergence of new variants of the virus, many of which have enhanced levels of infectivity.


Of course, even seemingly benign methods like wastewater surveillance can have unintended consequences.

One possible problem the paper raises is the issue of privacy. As it stands, methods of surveillance are rife with the potential for mission creep. This occurs in a situation where data collected from contact tracing, say, location tracking or credit-card transactions, is used outside of its intended purpose.

There is also the fact that underprivileged groups in society already tend to be heavily monitored; wastewater surveillance may exacerbate this, subjecting already-vulnerable groups to over-surveillance and the restrictive policies that may accompany it.

Ultimately, the success of wastewater surveillance will depend on public legitimacy and trust of such measures, according to the paper.

This means that efforts taken by the government need to be collaborative, engaging both civil organisations and public or private utilities in order to ensure that both the scale of data collected, and its usage, are appropriate.

When implemented, wastewater surveillance programmes should also be designed to pre-emptively combat privacy and inequality concerns. In situations where targeted surveillance of high-risk communities is necessary, as Singapore has done with the testing of wastewater at maintenance holes in foreign worker dormitories, it should be publicly disclosed.

Now, more than ever, public health officials need actionable, community-level information in order to make decisions. As the paper concludes, “Wastewater surveillance for infectious diseases should be a top priority.”

By Wong Xin Yi and Sophia SOH Fei Wen

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