Should you still wear a mask in public? Is it safe to attend concerts or travel right now? Experts are increasingly recommending that we consult COVID-19 wastewater data to make decisions like these. And, they say, the pandemic revealed the true potential of monitoring what’s in our poop.
Wastewater monitoring isn’t entirely new. Epidemiologists have been using it to keep track of polio outbreaks for decades, Amy Kirby, Ph.D., microbiologist and program lead for the National Wastewater Surveillance System at the Centers for Disease Control and Prevention, tells TODAY.com.
Before the pandemic, researchers knew they could find evidence of enteric viruses, which infect the gut, in wastewater samples, Yinyin Ye, Ph.D., assistant professor of civil, structural and environmental engineering at the University of Buffalo, tells TODAY.com.
It “makes sense” that we’d find viruses like those in feces and sewage, Ye says. But, before the pandemic, “people never thought wastewater could be used to track respiratory viruses,” she says. It wasn’t until COVID-19 came along that experts realized how helpful wastewater monitoring could be in tracking other types of viruses as well, she explains, including respiratory viruses.
As other COVID monitoring tools we once relied on have become less useful, wastewater is an increasingly valuable tool to make safer choices. Here’s what experts want you to know about COVID-19 wastewater monitoring and what those numbers mean for you.
When did COVID wastewater monitoring start?
Early in the pandemic, individual groups of researchers proved they could detect the coronavirus in wastewater, particularly on college campuses.
For instance, experts at the University of Arizona even used it to help contain an outbreak on campus as early as August 2020. In 2021, a group at Emory University used wastewater to spot a rise in COVID-19 on campus when students returned from spring break.
From there, the CDC began monitoring wastewater for COVID-19 in 2020 (the first widespread sewage monitoring program in the U.S., Kirby says), and ramped up the program in 2022.
Today, wastewater monitoring is also helping researchers keep tabs on other illnesses, such as Mpox, norovirus and hepatitis A.
What does COVID-19 wastewater data actually measure?
When people are infected with SARS-CoV-2, the virus that causes COVID-19, they shed bits of the virus in their feces — whether or not they have noticeable symptoms. That’s why the CDC started looking into wastewater monitoring for COVID in the first place, Kirby says.
“We were really focused on, how can we get a better idea of those people that are infected but may not have any symptoms or may have very mild symptoms?” she says. “We know they’re still going to shed virus in their feces, and so we can detect those cases (through wastewater monitoring) and look at how they impact the overall trends in a community.”
Ye and Kirby both noted that researchers still aren’t entirely sure why we shed this virus, a respiratory virus, in our stool. It could be a result of swallowing viral particles in respiratory secretions or of the virus replicating in the gut the same way foodborne illnesses do, Kirby says.
“We don’t know. But, for our purposes, it doesn’t really matter,” Kirby explains. “We know that it’s there and (that it’s a) great signal to understand what’s going on in the community.”
As it turned out, not only does wastewater reflect general trends in the spread of COVID-19 within a community, but it also does so relatively quickly. Throughout the pandemic, Kirby says, experts noted wastewater trends changing four to six days before case numbers or test positivity showed the same change.
“It really is the first sign that cases are starting to pick up in a community,” she says. “It’s also the first sign that cases are starting to go down,” which is a major advantage over other metrics.
Experts use a familiar test — polymerase chain reaction technology (PCR) — to look for viral RNA in untreated wastewater, explains Ye, whose team is involved with COVID wastewater monitoring for much of western New York. Depending on the type of PCR test the researchers use, they can also look for changes in the viral genetics, giving them a heads-up about possible shifts in coronavirus variants.
Different labs may have different protocols for detecting the viral particles, analyzing the data and making sure their results are accurate, Hoerger says. For example, if heavy rain dilutes rainwater, it can be challenging to account for that in interpretations, he says.
Ye stresses that public health officials are only looking at this data at the community level. They’re not monitoring wastewater at the individual or household level. (No one is keeping track of what you, as an individual, are pooping out.)
And, for the record, researchers believe the viral particles in feces to be inactive, Ye says. To date, no one has contracted COVID-19 via exposure to wastewater, the CDC says.
Why is wastewater monitoring so helpful right now?
In previous years, we may have relied on case numbers or test positivity to assess how much and how quickly COVID-19 was spreading in our area.
But those metrics “aren’t very useful anymore,” Hoerger says, for two major reasons: First, a lot of people aren’t getting tested at all anymore for COVID-19, he says. And, second, if they do get tested, that’s likely happening at home with a rapid test, which isn’t reported to any public health agency.
On the other hand, one major benefit of wastewater monitoring is that “it doesn’t require any individual to do any testing,” he explains. “It’s just tracking what’s going on in a community.”
Wastewater data also has the advantage of being highly local and, therefore, relevant to what’s going on in your area, Ye says.
Using COVID-19 wastewater data to guide your behavior
To find COVID-19 wastewater monitoring data in your area, take a look at your local public health department website. The CDC also keeps track of local sewage numbers and national numbers.
“We have about 1,500 sites that are doing testing, and that covers over 40% of the US population,” Kirby says. “So we’re covering a big chunk of the population.”
That said, if you don’t have local wastewater monitoring in your community, Hoerger recommends keeping an eye on the national or state-level numbers. “When things are getting bad nationally, there’s a good chance that things could be bad locally, or they’re about to be bad,” he says.
But local information is always going to be the most helpful, Ye says, noting that trends can be different from county to county. And rural areas, which often aren’t connected to larger sewage systems, may not be counted in those estimates, she explains. Researchers are working on ways to reach those areas right now, she says.
Also, keep in mind that the numbers you’re seeing on the dashboard may be a week or two behind what’s actually happening in the community, Hoerger says. For example, Ye says the samples for her lab are typically collected once or twice per week, and those numbers are included in health department updates the following Monday or Friday.
It’s not entirely clear how wastewater numbers may translate to actual case numbers in the community. But spikes in wastewater monitoring generally do mirror spikes in actual COVID-19 cases.
“There’s not a direct correlation,” Kirby explains, “(but) we know that when you see so wastewater concentrations increase twofold, cases in the community have also increased twofold.”
If you see numbers starting to increase, the experts say that’s an indication that it may be time to take more precautions, such as:
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Start wearing a mask in public spaces (like mass transit) again if you previously stopped doing so.
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Get your updated vaccine or booster if you’re eligible.
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Skip or limit crowded, indoor events. Or, if you’re hosting an event, consider taking it outside.
Additionally, when traveling, Ye checks wastewater trends for her destination to plan out what precautions she may need to take.
When looking at the data, you don’t need to get deep into what the specific numbers might mean, Kirby says. “Focus on the trends and not so much the levels,” she says. “That’s the best way (for the general public) to interpret that data.” The CDC wastewater trends dashboards are designed to be intuitive and used for this exact purpose, she adds.
Both Kirby and Ye recommend thinking of wastewater monitoring data “like a weather report” for health. In the future, Ye hopes “we can use wastewater data as a kind of forecast to tell us if there’s a higher possibility you’ll get COVID tomorrow.”
For now, Kirby hopes people check the data to decide if they should wear a mask on public transit or scale back on indoor events, for instance. Incorporating that kind of decision-making into your day-to-day, Kirby says, “will go a long way to keeping communities healthy.”
This article was originally published on TODAY.com
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