With coronavirus testing still lagging behind targets, health officials are searching for other ways to assess the spread of the outbreak. One possibility? Looking at what we flush.
The coronavirus SARS-CoV-2 is often spread through sneezes and coughs, but it also leaves the human body through our waste. Scientists around the world are now testing sewage for the virus, using it as a collective sample to measure infection levels among thousands of people.
While the field of wastewater epidemiology existed before the coronavirus pandemic began, it's rapidly expanding in the hope it can become a front-line public health tool.
"Normally when I tell people I work with poo, they're not super-interested," Stephanie Loeb, a postdoctoral researcher at Stanford University, told NPR in an interview over Skype. But she said: "There's really a lot of information in our waste."
In the basement of a university building, Loeb pulls samples from freezers filled with vials of raw sewage, collected regularly from 25 wastewater treatment plants around California. Each is a snapshot of that community's health.
"It's this perfect mix, you know," said Krista Wigginton, a professor of environmental engineering at the University of Michigan who also is working on the Stanford project. "The entire community is putting samples in at the same time."
She said by the time the virus reaches wastewater treatment plants, it's still possible to read its RNA.
"These are virus particles that are mostly intact but that are no longer infective," Wigginton said. "That's what it looks like at this point."
The idea is that measuring overall virus levels in sewage over time could indicate whether an outbreak is growing or shrinking, potentially showing that trend earlier than patient testing would.
"That's a real-time measurement of what's happening in the community," Wigginton said. "Whereas some other tools we have, like the number of confirmed cases in clinics, sometimes those are delayed by quite a bit of time because people don't go get checked until maybe their illness has progressed by quite a bit."
The approach is already used for other diseases such as polio. Health officials are working to eradicate polio around the globe, and in Israel, an outbreak was spotted early through the wastewater system.
The Stanford team isn't the only group working on coronavirus detection in sewage.
"We have a lot of nicknames," said Newsha Ghaeli, co-founder of the startup Biobot Analytics. "I think some of our customers joke around that we're the 'sewer girls.' "
Biobot is testing sewage from about 150 communities across the United States. Originally, the company was using sewage to monitor the opioid crisis, but it quickly started offering coronavirus testing.
"It really caught fire," Ghaeli said. "Within 10 days, we hit internal capacity."
Ghaeli said that in some cities they've been able to detect the coronavirus in sewage the same week the first cases appeared. Other projects in France and the Netherlands have produced similar results.
In a more challenging scientific feat, Biobot is also working to estimate the number of individuals who have the coronavirus in a community, based on the levels found in sewage.
Calculating that depends on knowing how much virus individuals shed, and some people seem to shed for a longer time than others, complicating the math. Other things could also affect the virus levels, such as how long it takes for wastewater to reach a treatment plant and rainy weather, which causes runoff to flow into the sewage system in some communities, diluting the samples.
"There's a lot of research that needs to be done before we can say this number in wastewater means this many cases in the community," Wigginton said.
The advantage of testing sewage is that it may capture individuals who are less likely to go to a doctor's office.
"Every person that is using the toilet has a voice," said Mariana Matus, Biobot's other co-founder. "And they can be taken into account for public health resources and prioritization of resources."
While it's still early in the technology's development, some see it being helpful in detecting new waves of an outbreak.
"I think it is potentially a new role that utilities can play," said Doug Yoder, deputy director of the Miami-Dade County Water and Sewer Department in Florida, which serves 2.3 million people. "There has been, at the community level, not a whole lot of data about conditions communitywide."
For six weeks now, Miami-Dade County has been sending Biobot sewage samples, which have shown the area's virus levels going up and down a bit.
"We've seen in a couple [of] instances the virus counts increase by a factor of six," he said. "And then the week following, it went back down. This data may not yet be ready for prime time in terms of community decision-making, but it has potential and promise for being able to see trends."
Health officials are eager for the information, he said, as one more way to gauge what's really happening with their local outbreak.
ARI SHAPIRO, HOST:
Communities around the country are looking for better ways to track their coronavirus outbreaks. One potential source could be in what you flush. NPR's Lauren Sommer reports on a new effort to measure the spread of the coronavirus through sewage.
LAUREN SOMMER, BYLINE: If you're infected with the coronavirus, it leaves your body through coughs and sneezes. But it also comes out the other end.
STEPHANIE LOEB: There's really a lot of information in our waste.
SOMMER: Stephanie Loeb is a postdoc at Stanford University. Her field of tracking human pathogens through our waste has been getting a lot of attention lately.
LOEB: Normally, when I tell people I work with poo, they're not super interested (laughter).
SOMMER: In her lab, which she showed me on Skype, she opens a freezer full of small vials of solids, as she calls them.
LOEB: Yep. It's all sorts of shades of that same color, sometimes darker and sometimes lighter (laughter).
SOMMER: Yeah, it's a freezer of raw sewage sampled from 25 wastewater treatment plants around California. But look at it another way. It's a health record for tens of thousands of people.
KRISTA WIGGINTON: It's this perfect mix. You know, the entire community is putting samples in at the same time.
SOMMER: Krista Wigginton is a professor of environmental engineering at the University of Michigan who is also working on the Stanford project. They're testing all those sewage samples for the coronavirus. The idea is that the more coronavirus cases spread in a community, the more shows up in the sewer system.
WIGGINTON: What's nice about that is it's a real-time measurement of what's happening in the community and what's being excreted in a community.
SOMMER: Which could provide an earlier warning than the tests that are run at a doctor's office.
WIGGINTON: Sometimes those are delayed by quite a bit of time because people don't go get checked until maybe their illness has progressed quite a bit.
SOMMER: This approach is already being used to detect outbreaks of polio in some countries. And the Stanford group isn't the only one trying to track coronavirus this way.
NEWSHA GHAELI: We have a lot of nicknames (laughter). I think some of our customers joke around that, you know, we're the sewer girls.
SOMMER: Newsha Ghaeli is a co-founder of Biobot, a startup that's testing sewage from 150 communities around the U.S. Originally, the company was using sewage to monitor the opioid crisis but quickly started offering coronavirus testing.
GHAELI: It really caught fire. Within 10 days, we hit internal capacity.
SOMMER: Ghaeli says in some cities, they've been able to detect coronavirus in sewage the same week the first cases popped up. They're working on using that information to extrapolate about how many people have the virus in a community. Scientifically, that's a bit trickier because you need to know how much virus a person usually sheds and for how long. But the company sees this technology playing a big role in detecting new waves of the outbreak.
GHAELI: Even once we do open up our cities again and we do go back to work again, it's very valuable for us to have a robust surveillance system in place.
DOUG YODER: I think it is potentially a new role that utilities can play.
SOMMER: Doug Yoder is deputy director of the Miami-Dade Water and Sewer Department in Florida. He's been sending samples to Biobot for six weeks now, which have shown their virus levels are going up and down a bit.
YODER: This data may not yet be ready for prime time in terms of community decision-making but that it definitely has potential and promise for being able to see trends.
SOMMER: Health officials are eager for the information, he says, as one more way to gauge what's really happening with their local outbreaks.
Lauren Sommer, NPR News.
(SOUNDBITE OF LEIFUR JAMES' "MUMMA DON'T TELL") Transcript provided by NPR, Copyright NPR.