Researchers explore whether human poop can help track COVID-19, and curb a second wave

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The early detection of a second wave of COVID-19 could start with a simple flush, says the co-founder of a company testing wastewater for the virus.

"Infected patients are excreting the novel coronavirus, SARS-CoV-2, in stool," said Newsha Ghaeli, co-founder of Mass.-based company Biobot.

"That's how we end up being able to see the coronavirus, along with a whole bunch of other human health information in our city sewer system," she told The Current's Matt Galloway. 

Biobot has been building a picture of the spread of COVID-19 through samples collected from wastewater facilities across the U.S. This week, its sample size has grown to include 300 facilities across 40 states.

Through lab testing, the company is "able to measure the concentration of the virus, and then convert that concentration into an estimated number of cases in a given community," Ghaeli said.

While the sample sizes are currently tied to the catchment of the wastewater facility itself, Ghaeli argued the scale could be adjusted by collecting samples "directly from the sewer lines, in order to get more community-by-community level information."

"That big picture estimation is very helpful in helping us understand how is the virus trending over time … do we see the amount of virus decreasing or increasing?" she said. 

That could be key to the early detection of a second wave once physical distancing measures have been lifted, she said, noting that most countries don't have the resources to implement regular, population-wide testing.

"We need a way to very easily and rapidly get a snapshot of what's happening at that aggregated city view," she told Galloway.

"It's very important that we have a robust surveillance infrastructure in place to be able to detect any new outbreaks and immediately contain them, whether that means re-implementing social distancing," she said.

Models have 'degree of uncertainty'

Researchers worldwide are analyzing human waste to detect and trace COVID-19, but some warn the models generated come with limitations.

Scientist Natalie Prystajecky started to test wastewater in B.C. for COVID-19 on Monday, but remains cautious about what findings the project will yield.

"What the end utility of this tool is, we still don't know … nobody's really done it in an active surveillance system yet," said Prystajecky, an environmental microbiologist with the University of British Columbia. 

"I would caution people from using it as an absolute truth and recognizing that often with models, there can be a high degree of uncertainty," she said.

"I would just want people to make sure that they understood the limitations of the data, as they interpret it."

In France, Vincent Marechal and his team have been testing wastewater since March 5 — less than two weeks before the country implemented a strict lockdown.

"What we've seen is a gradual increase of the viral load in wastewaters up to the 10th of April," said Marechal, a human virologist with the Sorbonne in Paris, where three Paris wastewater treatment plants were studied.  

After that, the viral load decreased, which he thinks indicates "that the lockdown procedure has been efficient."

However, despite a decrease in those initial weeks, the concentration of the virus in the water stabilized in the weeks that followed, even as confirmed COVID-19 cases have dropped off, he noted.

Marechal said that might mean mild and asymptomatic cases are still spreading — possibly as people circumvent lockdown orders — or it might mean the virus can be present in stool or urine for longer than thought.

"We are missing some information, and for us it's very difficult to infer — from what we get in the water — the number of infected people in the population," he said.

Despite that, Marechal thinks wastewater tests could give a general indication of the virus in areas with asymptomatic carriers in a cost-effective way.

"Wastewater helps you to investigate what happens in thousands of guts," he told Galloway.

"Instead of testing each person, you can just stay in a specific area, 'OK, the virus is probably here because the wastewaters are positive for the virus,'" he said.

"We can go back to people and say, 'OK, take care guys, because it's not working, the virus is back.'"

Written by Padraig Moran. Produced by Peter Mitton and Arman Aghbali.