Sewage Doesn’t Lie: New Method to Monitor COVID


Sean Norman, MS, PhD: “We know from the scientific literature that asymptomatic and symptomatic individuals both shed the virus through fecal material, which then works its way into the sewer system, and it can be captured as part of our sample.”

Pool testing has been mentioned by healthcare experts as one way to monitor and control community spread of coronavirus disease 2019 (COVID-19) since almost the beginning of the pandemic. Of course, some pools one doesn’t want to deal with unless you’re Sean Norman, MS, PhD, an associate professor and the director of the molecular microbial ecology laboratory at the University of South Carolina. Norman is running an experiment in which the community levels of COVID are found in sewage samples. He says that this would not replace the need for individuals to be tested for the coronavirus, but it would collect valuable data that can measure trends that would include asymptomatic as well as symptomatic carriers. “If the individual level testing goes down, or is decreased, the sewage is still going to pick up on those same individuals within that catchment population,” says Norman.

Infection Control Today®: Would sewage surveillance be an effective way to track COVID-19 in communities?

Sean Norman, MS, PhD: Well, let me first of all say that this is not meant to be a replacement for individual level testing. However, it’s meant to be a supplement or an additive to individual level testing. And the reason this works so well, is because we in sewage surveillance, you do not necessarily have to worry about testing capabilities. You don’t have to worry about individual level participation in testing. This provides a composite sample of whatever scale that you would like to measure. You know, we measure a lot of times at a community level, where we’re taking composite samples from a wastewater treatment plant, which represents a sample from every individual that contributes to what we call the catchment population. That is the entire population of people that are connected to a municipal sewage system. All that material goes to a wastewater treatment plant. And if you can collect a 24-hour composite sample from one of these sites, then you’re able to capture a sample from almost everybody that would be within that that catchment population. Then you can test for the abundance of the virus. This becomes very advantageous when you talk about trying to understand how prevalent the virus is in community settings. Because you’re able to then take that number and convey it back to, or relate it back to, the abundance of the virus within that entire catchment population. And that, for the most part, does not depend on the level of testing that is occurring within that community setting. This is independent of individual level testing. So if an area does not have the capacity to test individuals at a high level, or individuals are not coming out, they’re not volunteering at a high level to be tested, then this provides a compromise that can be used to supplement and to support what you might be seeing within a community setting. For instance, if case numbers are going up, you might see that supported by the increase abundance of SARS-CoV-2 virus in the sewage. Now, if that number of cases start decreasing, some people might question whether the number is decreasing because less testing is occurring. Sewage surveillance provides an avenue to really support the trends that you’re seeing in case numbers in the fact that the abundance of the virus in the sewage is going to be independent of any of these other variables. If the individual level testing goes down, or is decreased, the sewage is still going to pick up on those same individuals within that catchment population. If we see decreasing trends and the abundance of the virus in sewage, we can relate that back, saying there must be a decreasing abundance of the virus within that community. And increasing as well.

ICT®: Can you capture asymptomatic as well as symptomatic carries this way?

Norman: Yes, you can. You can catch asymptomatic as well as symptomatic. We know from the scientific literature that asymptomatic and symptomatic individuals both shed the virus through fecal material, which then works its way into the sewer system, and it can be captured as part of our sample. So that’s also another advantageous part about this process is that you are likely to catch people before the cases are seen, because you’re catching them when they’re asymptomatic. Before they might have a chance to spread the virus, for instance. You can you understand what the total level is of that community.

ICT®: Is this a new monitoring process?

Norman: Sewer surveillance has been used for other things. It’s been used for polio. It has been used for norovirus. It’s been used for opioids to understand uses of opioids in communities. It’s been used before. Now, when this current pandemic started, sewage surveillance started picking up around the world. Some groups in the Netherlands were some of the first to kind of start doing this, showing that you can find the virus in sewage. Then it has kind of migrated around the globe with people starting to use this technology. We here in my lab, are in partnership with the CDC and the South Carolina Department of Health and Environmental Control. We’re using it to look statewide at eight different wastewater treatment plants in South Carolina, two in Texas, and then one in California, to really try to understand the prevalence of the virus and identify trends: upward trends and downward trends. You know, one thing I can say, from our perspective in our state here is it really did show that when we passed mandatory mask policies—when those were put in place—we saw a sharp decline in the abundance of the virus across sewer sheds in the state, which is really a good measure to support the policy changes that were made to show that these policies were indeed having an impact on the abundance of the virus.

ICT®: How long has this been going on?

Norman: Our particular sampling, we started optimizing in early March. It was deployed in our entire system in mid-April.

ICT®: Is the CDC funding this?

Norman: The CDC is funding some of this as well as the South Carolina Department of Health and Environmental Control.

ICT®: Is this catching on in other places?

Norman: It is catching on. I know, there are several groups working in collaboration with the CDC to generate what we call a national sewage surveillance type network. A lot of people will be using the data from our individual lab to help the CDC generate models that will then be used at a national level. But that’s far, far in the future, once we understand how this technology can be used for this particular virus.

ICT®: Is the process expensive? Does it take a long time? Is it complicated?

Norman: It’s not. From my perspective, it’s not very complicated. It’s some of the same technologies that you would use to do the clinical testing. Now, that said, there’s a lot of pretreatment you have to do with sewage samples because they’re pretty dirty samples, right? You have to do a lot to clean the samples up to be able to do the molecular base methods to identify and quantitate the virus in the subsequent samples. It’s really a matter of having a good network. I work with partnerships with the utilities. My lab would have a hard time doing all of this on our own. We partner with utilities. And we partner with our Department of Health and Environmental Control. And through that partnership, we’re able to get samples delivered to the lab. We go collect some samples, the operators at some of the utilities are collecting samples for us. And once all that’s done, we bring that back to my lab or they get brought to my lab where we then preprocess and then analyze the samples. And so, on a cost analysis, it’s not incredibly costly. There’s some upfront cost and some of the supplies needed. But once you overcome some of those upfront costs, it becomes fairly manageable.

ICT®: And it would take a while before this can be launched nationwide. Why would you think that is?

Norman: Well because we’re trying to understand a lot of the details. What could impact the abundance of the virus in sewage. So, we get a measurement at a wastewater treatment plant. We know the viability of the virus may not be long lived. Meaning we might see a signal in the sewage, but what does that mean? Can you calculate back into the community what the abundance is? How much of the virus signal do you actually lose by the time it makes it to the wastewater treatment plant? We might get a number at the wastewater treatment plant of viral recoveries per liter of sewage, for instance. Now, what does that actually mean? You know, if we’re only capturing, say, 10% of that, and we know our viral recoveries are only maybe 10%, or 20%, we can then factor that into calculations. But there are a lot of things we don’t know about it. We can use it currently to look at trends: up and down trends. But if we really want to be able to go back and understand the true abundance of the virus in the community, like be able to put a number to it, as well as be able to identify maybe how many people have cases of COVID, be they either asymptomatic or symptomatic, within that area, we have to know a lot more of the details about how the virus survives in sewage. How it’s diluted, because in wastewater treatment plants, you have a lot of pipes, right? These pipes leak a lot of times. If you get an area where there’s a heavy rainstorm, that can cause leakage into the sewage system, which then dilutes the samples. The number of the virus that you get in sewage might be diluted. A lot of work is going on right now across the country trying to understand a lot of the technology and to work out what we call the standard operating procedures. To try to understand what are the best practices for doing sewage surveillance.

ICT®: Is there a lag time? Does what you discover happening in a community happened two weeks ago?

Norman: I’ll start by saying that oftentimes sewage provides a leading indicator. We actually know ahead of time what’s going to be happening in the community, because we get numbers from asymptomatic individuals. We also get numbers from people, possibly before they start showing symptoms. They could be asymptomatic, or they could just have delayed symptoms. We get the numbers. The virus is shed a little before some of those symptoms occur. Because of that, some people have indicated that they can get up to a week leading indicator from sewage. Still, it’s just important to know that this is a supplement to individual level testing. I don’t want anybody to think that this is trying to overtake individual level testing. But I think the two types of testing, working in concert, provide more certainty in what in the data … the overall data that we’re seeing.

This interview has been edited for clarity and length.

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