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Testing wastewater can reveal the prevalence of COVID-19 (and potentially particular variants) in a community, regardless of whether individual residents are getting tested. The Centers for Disease Control and Prevention (CDC) has developed a national system to coordinate the tracking of COVID-19 via sewage in 37 states, four cities, and two territories.
On October 6, 2021, SciLine interviewed: Dr. Amy Kirby, an environmental microbiologist in the Waterborne Disease Prevention Branch and the Program Lead for the National Wastewater Surveillance System (NWSS) at CDC. She spoke about topics including: how testing wastewater can predict trends in cases before they can be detected by clinical testing; how municipalities can use sewage data to decide where and when to allocate resources to test for and/or treat COVID-19; how the CDC is using the National Wastewater Surveillance System; and how institutions such as nursing homes, colleges, and prisons can use this technique to manage COVID-19.
AMY KIRBY: My name is Amy Kirby. I’m the program lead for the National Wastewater Surveillance System, and we study how to track diseases using wastewater to understand what is circulating in our communities.
Interview with SciLine
What is the National Wastewater Surveillance System, and how does CDC use it?
AMY KIRBY: So CDC established the National Wastewater Surveillance System, or NWSS, in September of 2020. And NWSS was designed to provide community-level information specifically on COVID infections in the community so that we can understand which communities are seeing increasing rates and which communities are seeing decreasing rates. And it has been very successful, and we are still using it for that purpose—to identify where the hot spots are for infection, where we can deploy more resources to support our public health jurisdictions and make sure that they have everything that they need to control the COVID-19 pandemic.
How can testing wastewater predict trends in COVID-19 cases before they can be detected by clinical testing?
AMY KIRBY: Wastewater has four main advantages that allow us to use it as an early warning system for COVID in communities.
The first is that it detects all types of infections. So people that are infected, whether they go on to have symptoms or not and whether you’re talking about adults or children, will shed fragments of the virus in their stool, and so we can detect that in wastewater. And so what we see in wastewater represents all of the infection types in a community.
Second—and what I think is actually most powerful—is that using wastewater surveillance isn’t—doesn’t rely on any kind of medical system, so it doesn’t matter if people that are infected go to the doctor or whether they have clinical testing available in their community. As long as they’re using a bathroom that’s connected to the sewer system, we can detect and track those cases in the community.
Third, it’s very efficient. So with one sample of incoming wastewater coming into a treatment plant, we can get information on hundreds, thousands, even millions of people in a community.
And finally, it’s fast. Our wastewater systems are very efficient, and they deliver waste from a toilet to the municipal treatment plant in just a few hours. And so we collect that sample and test it, and we can have that data in hand five to seven days after the toilet is flushed. And what that means is that we see trends in wastewater, on average, four to six days before we see those same trends in case reporting.
How are municipalities using sewage data?
AMY KIRBY: That’s been one of the most exciting things with NWSS, actually, is to see all of the ways that our health departments are using this data. And the one thing that we hear most consistently from our health department partners is that wastewater surveillance data gives them confidence that they know what’s going on in their communities.
As you may imagine, they’re looking at a lot of data, and it doesn’t always agree. And the fact that wastewater data is completely separate from medical care and testing means that it gives you slightly different information. And it can help you understand what’s going on in that clinical data. So that is, by far, the use that we’re hearing the most.
Of course, we’re also hearing them use this information to make decisions about resource allocation. So if you think about the role of a state health department, when they’re looking at all of the communities in their state, they need to make decisions about where to send mobile testing units, where to provide extra contact tracing support. And wastewater surveillance can be really useful for that—to understand which communities have increasing cases and which communities are having decreasing cases and may need less support.
How can institutions such as nursing homes, colleges, and correctional facilities use this technique to manage COVID-19?
AMY KIRBY: Wastewater surveillance was initially conceived as a community-level surveillance system—so taking samples at a municipal treatment plant to understand what’s going on in the whole community that’s served by that plant. But you can also think about wastewater surveillance for a single building—so looking at the wastewater coming out of a single building or facility. And the place where we’ve seen this deployed with the greatest success has been universities. So last year, there were lots of universities that were able to use wastewater surveillance to test the wastewater coming out of dormitories and understand which dorms were having cases so that they could then go into those dormitories and do additional testing and symptom screening to control those outbreaks before they got large.
And we are now trying to replicate that success that universities had in other facilities, like correctional facilities and nursing homes. And one of the keys for these facility-level uses of wastewater surveillance is having on-site testing. So you need to be able to take a sample and get a result that day as opposed to sending it off to a lab and getting the test back, you know, in five to seven days. So we currently have an evaluation study going on in correctional facilities to test an on-site testing kit. And we’re really excited to see how that performs.
Does sewage surveillance have potential for other diseases?
AMY KIRBY: The most exciting part for us is that although the National Wastewater Surveillance System was built to provide surveillance for COVID-19, it really can be used for a variety of pathogens. And so we’re already thinking about how we can expand this system to provide surveillance information on a variety of pathogens in our community. In this first expansion, we’re thinking about looking at targets such as antibiotic resistance, foodborne infections like E. coli and salmonella and norovirus as well as some emerging pathogens like the fungal pathogen Candida auris. And we expect to have those expanded analyses rolled out to our system within the next couple of years.
Public Health Jurisdictions with Funding for Wastewater Surveillance
As of September 27, 2021, the following state, local, and territorial public health departments have received funds from CDC in FY2021 to support wastewater surveillance activities. Funding levels and the extent of wastewater surveillance activities vary among jurisdictions.
- District of Columbia
- North Carolina
- New Hampshire
- New Mexico
- New York
- Puerto Rico
- Rhode Island
- South Carolina
- South Dakota
- West Virginia
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