How Sewage Samples Help Scientists Track COVID-19 Outbreaks

11:55 minutes

Modern Wastewater Treatment Plant, aerial view
A wastewater treatment facility. Credit: Shutterstock

This story is part of Science Friday’s coverage on the novel coronavirus, the agent of the disease COVID-19. Listen to experts discuss the spread, outbreak response, and treatment.

As coronavirus cases surge across the U.S., including in Texas, Florida, Arizona, and California, it’s more important than ever to have an accurate and real-time understanding of transmission. Epidemiologists have been measuring the spread of the virus based on the number of individual people who test positive. But depending on when people get tested, and how long it takes to get their results, confirmed cases can lag days behind actual infections. 

Luckily, there’s another way to find out where people are getting sick: The virus that causes COVID-19 can be detected in feces, and for months, researchers have been studying whether sampling sewage systems can help identify new outbreaks faster.

Scientific American technology editor Sophie Bushwick joins Ira to talk about the value of sewage tracing for COVID-19. Plus, a new sparrow song has gone viral in Canada, and why summer fireworks can damage not only your hearing, but also your lungs.

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Segment Guests

Sophie Bushwick

Sophie Bushwick is senior news editor at New Scientist in New York, New York. Previously, she was a senior editor at Popular Science and technology editor at Scientific American.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. A bit later in the hour, we’ll talk about how we can make the great outdoors a safe and inclusive place for everyone. But first, the pandemic is worsening in the United States, and the records keep shattering. This week we saw the number of new daily cases topped 50,000 for the first time, and case numbers are rising in 40 states, but all of those case numbers rely on thousands of individuals getting tested, which as we’ve seen throughout the pandemic, can be difficult, depending on where you are, and there’s a time delay.

But what if you could see we’re COVID was peaking before the test results come back? Here to talk about one potential surveillance method, sewage, is Scientific American Technology editor Sophie Bushwick. Sophie, welcome back.


IRA FLATOW: You know, you’ve started with one of my favorite topics, sewage. We’ll talk about that at some other time.

SOPHIE BUSHWICK: Well, sewage is an amazing thing because it’s not limited by wealth or by ability to access tests. Everybody poops. And in an area with a working sewage system, we’ve got this way to surveil an entire population. So before the pandemic, researchers had been using this method to look at the use of drugs in an area, and now, they’re able to find viral RNA from the novel coronavirus in sewage, and people– it’s not just in the US. People all over the world have been looking at this as a method of tracking the novel coronavirus.

One group in Spain found that they detected coronavirus in the sewage of an area before any positive tests started coming in. So it could provide a way to spot when an outbreak is about to happen.

IRA FLATOW: Now we’re seeing a lot of outbreaks around the country. Could we have seen them and detected them sooner by looking at their sewage systems?

SOPHIE BUSHWICK: So it’s still a little bit of a new tool, and it’s definitely going to have limitations. For example, it’s hard to tell, you know, what the concentration of RNA in a sewage sample, how does that translate to the number of people who are actually sick. So this is something that’s still being worked out. Some studies have suggested that the concentration of RNA in sewage means that there’s more people who are infected with coronavirus than have shown up in the official test counts, but there’s not an exact equation to translate between people and concentration. So it’s definitely still something that researchers are working on.

IRA FLATOW: And on the treatment side of things, a story about how hospitals are trying to treat COVID-19 without waiting for drug trials. What’s going on there?

SOPHIE BUSHWICK: Under normal circumstances, if there is a disease, you want to make sure that the drug used to test it is going to help more than it hurts. So that often involves doing the long clinical trial and waiting for FDA approval and making sure that the information gets published in a peer reviewed journal. But during the pandemic, a lot of doctors are being forced to look at experimental treatments that maybe haven’t been backed up as much as they like. Maybe they come from a preprint study.

So instead of just relying on papers and clinical trials, doctors are talking amongst themselves. They’re discussing how medication has turned out for their patients, and some are more willing to apply still unclear medications. Others are being much more cautious and saying, look, we know that treating with oxygen and electrolytes helps. But the other ones, it’s unclear whether they’ll help more than they hurt.

IRA FLATOW: Which other ones are they trying?

SOPHIE BUSHWICK: So for example, we now know that one of the symptoms of COVID-19 is an increase in blood clots, which can cause all kinds of problems in the human body. But earlier in the pandemic, doctors saw that patients had all these symptoms that could be suggestive of blood clots, but they weren’t sure if that’s what was going on. And so they didn’t necessarily want to give them anti-clotting medication, which can have negative side effects, until they had a better idea. And so they had to figure out ways to scan their patients without infecting the rest of the hospital to make sure that blood clots were really happening. And then they had to treat them and see what the outcomes were, and now it’s become a much more standard treatment for doctors to use anticoagulant drugs on COVID-19 patients.

IRA FLATOW: So they’re making these ethical choices as they go along.

SOPHIE BUSHWICK: That’s right. The other thing is that they’re dealing with pressure often from patients’ families who want to know that the hospital’s doing everything they can to help their loved ones, and it’s very difficult because I think as humans, we all have this idea that doing something is better than doing nothing, and that we want to try every possible method of treatment, but doctors are faced with the idea that some of these treatments might not help very much and could have more harmful effects, which is something that happened with hydroxychloroquine when that drug was still being touted as a potential treatment.

IRA FLATOW: Let’s move on to a different virus, but possibly the same problem, a story about how a strain of swine flu has shown the potential to infect humans. How should I feel about this, Sophie?

SOPHIE BUSHWICK: Not great. So the good news– the good news–

IRA FLATOW: There is good news.

SOPHIE BUSHWICK: The silver lining is that this is something that is not yet causing disease in humans. But this is something that scientists are saying we need to keep an eye on this, because swine flu has shown that it can mutate to be spread in humans. So this is a particular strain of swine flu called G4EA H1N1, and researchers have found it in pig farms in China since 2016. So it’s not new.

But this new study looked at this strain of H1N1 in humans, and they found that it does infect human airway cells. So so far, it hasn’t caused disease in the people it’s infected, but they’re sounding the alarm that if this were to mutate or adapt, it could perhaps cause disease in humans, and then it would have the potential to turn into another pandemic.

IRA FLATOW: All right, let’s talk now about a different kind of viral, a bird song that went viral. Tell us about that.

SOPHIE BUSHWICK: Yes, this is definitely the kind of viral that we all prefer. So birds tend to be creatures of habit. You know, they’ll sing the same birdsong over generations, but researchers in Canada found that the white throated sparrow was shaking things up and that a particular regional variation on their typical song was spreading through other populations and really, yes, going viral across the country.

IRA FLATOW: The story here is that the birdsong morphed, it changed as it went around?

SOPHIE BUSHWICK: Right. So researchers looked at a website where citizen scientists had uploaded clips of white throated sparrow song, and what they heard was that a version of the song– the typical version of the song had a three-note ending, and they found that, all of a sudden, some of the birds were singing a two-note ending, and that was spreading and replacing the original version.

IRA FLATOW: All right, let’s listen to a clip from the original version.


And let’s listen to the hot new song.


Now, Sophie, I hope you can hear the difference because–

SOPHIE BUSHWICK: I think if I was a sparrow, it would make more of a difference to me.

IRA FLATOW: Is the new song better somehow? I mean, why would you have a new song? I guess there must be some reason why it changes.

SOPHIE BUSHWICK: Right. So they’re still trying to figure that out. So they think they know how it has spread. They put little backpacks on the sparrows to track them as they moved, and they found that sparrows that sung the new song had the same over wintering grounds as sparrows that sang the old song, and so they think that juvenile males learned this new song during this winter season. But what they don’t know is why that song would be better. They haven’t found that it helps sparrows defend their territory, so they think that maybe female sparrows are more attracted to males that sang this new song, and that could account for its success.

IRA FLATOW: Let’s talk about this weekend coming up. The 4th of July is this weekend, and you’ve got some new fireworks science that, frankly, I’m not excited about, having been to many fireworks displays. Please tell us more about it.

SOPHIE BUSHWICK: Right. So we all know that if you are setting off fireworks, you need to be very careful to avoid explosions and injury that way. But there is another danger, which is that a lot of these fireworks emit toxic substances, so chemicals and metals, like lead and copper. And researchers wanted to see what effect these have on human lung cells and on animals. And so they basically bought about a dozen different types of common fireworks and set them off in the lab, and then they took samples of the substances that were emitted, and they exposed human lung cells and live rodents to these different substances.

And they found that at least two of the fireworks emitted lead in levels that were harmful and that other ones managed to damage lung cells. In particular, a firework called The Black Cuckoo was the most toxic, and it was 10 times more damaging to human cells than a neutral saline solution.

IRA FLATOW: Wow. I’m glad– I guess that’s the good news and bad news. The good news is we know about it. We can stay away from it. The bad news is that it’s happening at all and just don’t suck in the fumes, right?

SOPHIE BUSHWICK: Right. Try to– I mean, yeah, try to avoid inhaling near fireworks, I guess.

IRA FLATOW: All right, let’s close it out with fireworks of a different kind, Sophie. Merging black holes. Scientists think that they’ve seen fireworks sort of a flash of light from this now?

SOPHIE BUSHWICK: Yes, this is really exciting. So back in May, astronomers using the gravitational wave observatory LIGO detected gravitational waves that they say came from a collision of two black holes. But then over the next couple weeks, there was a flare of light coming from the same part of the sky. So what they’re saying is this light could have been produced in the merger.

IRA FLATOW: How would that happen? Why would the merger cause the light?

SOPHIE BUSHWICK: Right. So we all know black holes are famous for not letting light out. So how is it possible that they produced light? So what these astronomers are suggesting is that if there was dust and gas around the black holes in what’s called an accretion disk, when the black holes merged and released all this energy, that could have caused a bunch of heat in this matter nearby, and it’s that matter that’s producing the light.

IRA FLATOW: Well, I would imagine that because physicists like rigorous evidence, there’s going to be some controversy going on here, right?

SOPHIE BUSHWICK: Oh, yeah. There are astronomers who say this is absolutely not what happened. This is a big leap, and it’s– I completely disagree with your findings. So there’s definitely– this is not a sure thing. It’s not a sure thing that this happened. It’s something that’s very much still up for debate.

IRA FLATOW: Well, it’s a sure thing that we love having you coming on, Sophie.


IRA FLATOW: Sophie Bushwick technology editor for Scientific American. Always a pleasure. Have a great holiday weekend.

SOPHIE BUSHWICK: Thanks. You, too.

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About Christie Taylor

Christie Taylor was a producer for Science Friday. Her days involved diligent research, too many phone calls for an introvert, and asking scientists if they have any audio of that narwhal heartbeat.

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Ira Flatow is the host and executive producer of Science FridayHis green thumb has revived many an office plant at death’s door.

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