This episode was filmed on June 2nd, 2020.

If we have more recent coverage of the pandemic, you'll find those episodes in our COVID-19 playlist, which is linked in the description. [ ♪INTRO ]. When dealing with a pandemic, information is power.

With a virus, for instance, knowing where it is and how many people are infected is essential for making good public health decisions — like, when to close down schools and businesses, and just as importantly, when we can safely reopen them. And with this latest virus, the one that causes COVID-19, we've mostly obtained that data by testing people who turn up with symptoms, then keeping track of the number of positive cases over time. But that method usually misses cases where a person's symptoms aren't severe enough or severe enough yet to get checked out.

Plus, it can be expensive and logistically challenging to do on a large scale. So right now, many places have a huge need for additional monitoring methods. And some scientists think they've found a good solution — one that wouldn't require individual tests, but could still track the infection and see which areas are getting hit hardest.

We're talking about sewage. Yep, you heard me right. Good ole poop.

To explain why, it's important to know that poop isn't just the remains of the food you ate. It also includes wastes your body wants to get rid of, like dead white blood cells, as well as microbes and viruses that get picked up along the way. This means you can use a person's poop to test for pathogens, including viral infections.

In a hospital, doctors might do this kind of test to help diagnose a patient. Outside of a hospital, things are a little bit more complicated. What you flush down the toilet doesn't come with a nametag. And by the time it arrives at a waste treatment plant, it's likely been mixed with countless other, y'know... samples.

But that's actually a good thing, in a way, because it means that instead of testing just one person, we can test a lot of people all at once — like, every pooper in the area! Once you have a sample from a sewage treatment plant, you can look for the viruses you want to know about, often with a technique called reverse-transcriptase PCR, which creates copies of viral genetic sequences so they can be detected. This is actually how most COVID-19 nasal swabs work.

And in sewage especially, scientists aren't just looking for whether the new coronavirus is present. They want to know how much of it is there, as that could help them estimate how many people in the area are infected. This technique has been used before to track viruses like norovirus, hepatitis, and polio.

And it turns out that the virus that causes COVID-19, SARS-CoV-2, can also show up in stool samples. This might be the result of people swallowing their own spit or mucus. But also, it looks like SARS-CoV-2 can infect and multiply in cells in the gut, which means the viruses may enter stool more directly, and even remain infectious.

Either way, their presence in feces means that we might be able to use wastewater treatment plants to test communities for COVID-19. And that's exactly what a couple of recent papers have tried. For instance, one proof-of-concept study in Australia was able to find SARS-CoV-2 RNA in wastewater.

And the estimate of the number of cases they obtained from the amount of virus detected was, quote, “in reasonable agreement” with clinical observations. There have also been a handful of pre-print papers looking into this. Pre-prints are scientific papers that are written up, but haven't yet undergone the peer review process, which is a critical step that can catch mistakes or oversights.

So we should take pre-prints with a grain of salt, but pre-prints from France, the Netherlands,. Massachusetts, and Connecticut have all found evidence that sewage testing might work. One factor scientists are still trying to nail down is the timing of everything.

We don't know when exactly the virus starts to appear in feces or how long it lasts. Work done with hospital patients seems to suggest that if the virus does show up in a person's poop, it usually happens after respiratory symptoms appear and can linger long after they've disappeared. But it's really hard to say for sure.

We don't usually have fecal samples from a person's first days after exposure to the virus or from people with mild infections — which might mean viruses are getting into wastewater before people show up at clinics. And one of the pre-prints, the one from Connecticut, found that jumps in viral RNA in a nearby waste treatment plant seemed to pre-date jumps in hospital admissions and positive nasal swabs by as much as a week. That suggests we could use sewage to predict where spikes in hospital admissions are going to happen, which would be a huge help.

Like, we could figure out which areas need to tighten up social distancing measures, or feel more confident in decisions to loosen them. Of course, before we get too excited about all this, we'll want to see what the scientists that review these pre-prints have to say. Plus, we'll need to see if patterns hold once people start actually traveling about again.

It's possible tourists could generate “false” spikes of sorts if they emit a bunch of viruses in their poop but don't actually seed a local outbreak — something that we might see in wastewater facilities near National Parks, for example. Also, because different treatment plants serve different communities and may follow different waste-handling procedures, we don't know if this will work or work the same at every plant. Finally, not everyone lives in places with waste treatment plants, like people with individual septic systems.

But! We know this technique's been useful for monitoring other diseases in the past. And while getting a nasal swab is invasive and personal, and requires you to go to a place, testing wastewater is something pretty unobtrusive and can effectively test a bunch of people all at once.

This means that, in the future, testing sewage could help us keep track of COVID-19, and maybe even help us get one step ahead of it. Thanks for watching this episode of SciShow News, which was made possible by the generous support of our patrons. To learn more about this awesome community of science-loving people, you can visit Patreon.com/SciShow.

And for more of our ongoing coverage of the COVID-19 pandemic, you can check out the playlist linked in the description. [ ♪OUTRO ].