Poop: Our Newest Ally in the Fight Against COVID-19?

Poop: Our Newest Ally in the Fight Against COVID-19?

Right now, scientists need additional COVID-19 monitoring methods. And our poops might help!

When dealing with a pandemic, informationis 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 safelyreopen them. And with this latest virus, the one that causesCOVID-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 wherea person’s symptoms aren’t severe enough or severe enough yet to get checked out. Plus, it can be expensive and logisticallychallenging to do on a large scale.

So right now, many places have a huge needfor additional monitoring methods. And some scientists think they’ve founda good solution — one that wouldn’t require individual tests, but could still track theinfection 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 thatpoop isn’t just the remains of the food you ate. It also includes wastes your body wants toget rid of, like dead white blood cells, as well as microbes and viruses that get pickedup along the way. This means you can use a person’s poop totest for pathogens, including viral infections. In a hospital, doctors might do this kindof test to help diagnose a patient. Outside of a hospital, things are a littlebit more complicated.

***What you flush down the toilet doesn’t come with a name tag. 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 allat once — like, every pooper in the area! Once you have a sample from a sewage treatmentplant, you can look for the viruses you want to know about, often with a technique calledreverse-transcriptase PCR, which creates copies of viral genetic sequences so they can bedetected. This is actually how most COVID-19 nasal swabswork. And in sewage especially, scientists aren’tjust 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 trackviruses like norovirus, hepatitis, and polio. And it turns out that the virus that causesCOVID-19, SARS-CoV-2, can also show up in stool samples. This might be the result of people swallowingtheir own spit or mucus. But also, it looks like SARS-CoV-2 can infectand 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 meansthat we might be able to use wastewater treatment plants to test communities for COVID-19. And that’s exactly what a couple of recentpapers have tried. For instance, one proof-of-concept study inAustralia was able to find SARS-CoV-2 RNA in waste water. 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-printpapers looking into this. Pre-prints are scientific papers that arewritten up, but haven’t yet undergone the peer review process, which is a critical stepthat can catch mistakes or oversights. So we should take pre-prints with a grainof salt, but pre-prints from France, the Netherlands, Massachusetts, and Connecticut have all foundevidence that sewage testing might work. One factor scientists are still trying tonail down is the timing of everything. We don’t know when exactly the virus startsto appear in feces or how long it lasts.

Work done with hospital patients seems tosuggest that if the virus does show up in a person’s poop, it usually happens afterrespiratory 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 froma 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 jumpsin hospital admissions and positive nasal swabs by as much as a week. That suggests we could use sewage to predictwhere spikes in hospital admissions are going to happen, which would be a huge help. Like, we could figure out which areas needto tighten up social distancing measures, or feel more confident in decisions to loosenthem.

Of course, before we get too excited aboutall 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 holdonce 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 alocal outbreak — something that we might see in wastewater facilities near NationalParks, for example. Also, because different treatment plants servedifferent communities and may follow different waste-handling procedures, we don’t knowif this will work or work the same at every plant. Finally, not everyone lives in places withwaste treatment plants, like people with individual septic systems. But! We know this technique’s been useful formonitoring other diseases in the past. And while getting a nasal swab is invasiveand personal, and requires you to go to a place, testing wastewater is something prettyunobtrusive 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.

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