Lately, the phrase “wastewater monitoring” has been making headlines, but what exactly is it? And why is it useful to researchers and public health experts trying to understand fluctuating levels of COVID-19 infection?
“Wastewater monitoring and analysis presents many challenges,” says Elena Naumova, chair of the Nutrition Data Science Division and professor at the Friedman School of Nutrition Science and Policy. “But it can be an incredibly valuable tool for getting a full picture of data on the prevalence of SARS-CoV-2 (the virus that causes COVID-19) in a given place at a given time. This image, she explains, can help shape public policy and keep communities informed of potential health hazards.
To better understand the science behind wastewater monitoring, Tufts Now spoke with Naumova about the methods and rationales behind the process, as well as the pros and cons of using it.
Tufts Now: How Does Wastewater Monitoring Work?
Elena Naumova: In the United States, samples of liquid wastewater and sludge are taken from approximately 930 wastewater treatment facility sites nationwide. It’s quite an accomplishment to have so many coordinating sites and agencies working together. Samples are taken from sewage ponds, which are community areas served by sewage collection systems, at treatment plants.
Samples are then sent to environmental or public health labs to be tested for SARS-CoV-2. Each sample undergoes laborious processing to measure the amount of SARS-CoV-2 ribonucleic acid (RNA) it contains. The amount of SARS-CoV-2 RNA in a given sample provides information about how much virus is present at any given time.
After processing, the data is analyzed and forwarded to the Centers for Disease Control and Protection (CDC). In order for viral levels to be compared between sampling sites and over time, the data must be converted so that they are normalized by population.
Here’s one way to understand how it works: Imagine having a glass of water that represents a particular population in the watershed and calculating the number of particles in the glass of water. You could say, I have six or 26 particles, but because each system serves a different number of people, no number means anything by itself.
But if you say that this glass of water represents 200 people served by a particular watershed, that gives you information you can use to make meaningful comparisons with samples from other systems.
Finally, the results are made public through the CDC’s COVID Data Tracker.
Why are public health efforts using this strategy now?
We have tools to check the nation’s vital signs; testing sewage gives us an extra one. To monitor health conditions accurately and reliably, we need many instruments with varying degrees of accuracy, convenience, and cost. Individual tests (using nasal swabs, for example) are the most accurate, but they are also invasive and expensive.
Routine non-invasive sampling, such as wastewater monitoring, is essential for public health professionals to inform authorities and the public of potential harm and also to establish regulations and policies and monitor their enforcement, but many factors can reduce the effectiveness of policies and monitoring.
The United States has been monitoring SARS-CoV-2 in sewage since September 2020. Some researchers believe that sewage monitoring may have the potential to identify changes in community infections earlier than clinical testing and allow for a faster public health response. Some think that if the sewage only confirms the trends already seen in clinical tests, it may not be the best investment.
By monitoring wastewater for pathogens, chemicals, and pharmaceuticals, we can learn more, and more quickly, about what might be happening in the population. We can monitor emerging trends. A combination of tools helps calibrate their use. Consider using both an EKG and a watch to check a pulse – both tools are useful, but one is best in severe conditions and another for everyday, routine use.
Wastewater sampling in combination with traditional hospital monitoring and contact tracing allows us to learn more about potential infection hotspots or unstable health conditions and the effectiveness of disease control measures. in a given community.
So it is effective, but it is not a golden ticket to identify epidemics, contain the virus and stop the pandemic?
It is complicated. The system is very useful when we understand its caveats.
One challenge is standardization. Wastewater is a complex and variable mixture, and often contains compounds that can interfere with RNA quantification methods, thus preventing accurate measurement. For each wastewater treatment site and at each stage of virus detection, all analytical methods must be well suited to the particular wastewater mixture. It is a chemically and biologically complex process that involves multiple steps that are difficult to standardize and require systematic controls.
Another challenge is that the number of people contributing to a given sewer basin can change over time, whether seasonally (due to tourism and holidays) or weekly (due to work-related travel or workers temporary). Or there may even be a day when no one leaves their house, for example because of a snowstorm. All of these factors will affect how much people contribute.
There is also the need for environmental benchmarking. Rainwater or industrial discharges can dilute wastewater samples and require adaptation of the test methodology. Sewage also contains RNA from dogs, cats and other animals, all potential hosts for the variant. Contaminants such as animal waste can compromise the interpretation of samples: the origin of detected pathogens is not always clear.
Another factor is affordability: the potential savings from wastewater monitoring are unclear. As the Government Accountability Office puts it, “wastewater monitoring can be particularly useful where clinical testing is resource-constrained, but quantifying the value is difficult due to a lack of cost-benefit analyses”. Combined tests for pathogens and chemicals, such as opioids, require different processes and more complex logistics.
Finally, there are privacy and ethical issues: wastewater data could be linked to identifiable data, especially in smaller communities, and this is a potential privacy issue. What happens if genetic data is misused? What if communities face consequences because surveillance suggests the spread of pathogens or the use of illicit drugs?
In low-income communities, individual testing may be prohibitively expensive or difficult to obtain. Does wastewater monitoring help address equity issues?
Not really, unfortunately. Much depends on available resources and political will. And the public health utility of monitoring wastewater for SARS-CoV-2 has yet to be fully demonstrated in low-resource waste systems — for example, systems with heavily decaying infrastructure — or environmental waters impacted by sewage.
As the CDC put it, “These systems have unknown fecal inflow and outflow and are open to environmental processes that have an unpredictable impact on the persistence of SARS-CoV-2 RNA throughout the system, including sunlight, predation by other microorganisms, and varying pH and temperature. . »
In addition, many of these communities could be serviced by septic systems. According to the Environmental Protection Agency, more than 60 million people in the United States, or about 20% of households, are. These systems are not connected to wastewater treatment plants, where sampling often takes place. Communities and households that rely primarily on septic systems are not represented in wastewater monitoring data.
Given all of this, is wastewater monitoring still a worthwhile business?
In my opinion, this is a powerful approach, and it should be developed and expanded to cover testing for well known agents like influenza, rotavirus, norovirus, antibiotic resistant bacteria. It should also be used as a tool to detect new pathogens.
The entire infrastructure is configured to track existing or emerging diseases, so you can be constantly on the lookout. And there’s so much evidence right now that we need to be vigilant for anything that might arise, like monkey pox or new coronavirus variants.
Its greatest value is that it allows triangulation of data from multiple sources. This allows us to be more sure of our information. Ultimately, this could be a really reliable monitoring system. I liken it to weather monitoring.
We no longer wonder why we need thousands of monitoring stations for weather data, because we know that these stations provide essential information for early warnings about, for example, a tornado 15 minutes earlier than we would have otherwise these warnings. These stations are lifesaving devices.
The same is potentially true for wastewater monitoring systems. Sewage monitoring could be the next valuable tool for detecting emerging pathogens with the aim of reducing the risk of infection, amplification and spread – the goals of the ongoing STOP Spillover project led by Tufts.