Research Shows Sewers Could Be Key to Identifying, Stopping COVID-19 Outbreaks

Since mid-October, Smith’s team has collected wastewater twice a week from the line between two residence halls and the sewer main.

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Researchers at USC are confirming that an early indicator of COVID-19 in the community is found in our sewers. That’s because people with coronavirus shed it in their waste. And now, that research could have implications for students returning to the classroom sooner.

COVID-19 cases are reaching record highs in Southern California. Hospitals and intensive care units are packed as the number of positive tests has soared in recent weeks. But researchers have tracked another indicator, found in our sewer system.

“Athought the virus that causes COVID-19 is a respiratory virus, it's still in fact in many individuals gastrointestinal tract, and then it's shed in their waste,” explained Adam Smith, PhD, Associate Professor of Civil and Environmental Engineering at USC.

We first met Smith in July when he and his team were in the early months of their research, collecting wastewater samples and analyzing them for traces of COVID-19. In fact, the summer surge of coronavirus in Los Angeles County is reflected in the data they collected from three different wastewater treatment plants that mirrors the county’s positive COVID-19 case numbers.

“And then alarmingly, we see a very steep increase in that data that’s happening over the last several weeks,” said Smith, referencing the current winter surge.

Their research proves the connection, but samples taken from sewer plants can’t pinpoint specific areas of an outbreak.

“One of the challenges we have in Los Angeles is these are very large treatment plants. The smallest one serves 1 million people and the largest serves 4 million people, so it’s difficult to have actionable items from this data,” explained Smith.

But sampling on a smaller scale is a different story. Since mid-October, Smith’s team has collected wastewater twice a week from the line between two residence halls and the sewer main. The few students on campus also get tested for COVID-19 weekly. The sewage samples are tested in a lab on campus. Initially, there was no sign of the virus in the waste water, and no positive tests among the students.

Scientists believe sewers could be an early warning system. Carolyn Johnson reported on NBC4 News at 11 p.m. on Monday, Aug. 3, 2020.

“But then, in early December, we did start to get our first detects in those buildings,” said Smith. “And I think one of the benefits is it shows just how sensitive this method is. We have just one positive in the building and we can detect it in the wastewater sample."

Studies have shown wastewater is an early indicator of COVID-19, even before people are symptomatic, so monitoring the sewer line could catch COVID-19 cases before they spread.

“We think this was going to be a really nice indicator of potential infections in buildings, and maybe it will also help us reduce our reliance on the nasal and oral swabs that we’re doing now that are very expensive,” said Smith.

In fact, the cost to test a wastewater sample is about the same as just one COVID-19 test. So instead of testing all students weekly, the wastewater data could be used to determine when wide spread testing is needed, using health care resources more effectively. And that could have broader implications for the rest of our communities.

“You could roll this out in other businesses like an office building where you have somewhat of a stable population,” explained Smith. “I see this in residential buildings, office buildings, and we could roll this out on a community scale where we’re collecting wastewater from individual communities within LA County.”

The strategy could potentially identify cases sooner, and slow the spread of COVID-19.

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