About half of COVID-19 patients shed viral particles in their feces, which has prompted some scientists to warn that the virus could be transmitted through human waste.
UW researchers have found an upside to SARS-CoV-2 showing up in feces: using sewage water to test for COVID-19. Many groups around the world are testing for COVID-19 at wastewater treatment plants, but a group at the UW is testing at a community-specific level.
When testing at a wastewater treatment plant, the “SARS-CoV-2 signal reflects the entire city,” Mari Winkler, assistant professor in the department of civil & environmental engineering, said . “Whereas if you go down to pumping stations it is more reflective of a community or a neighborhood or a ZIP code.”
Winkler’s group started testing sewage water mid-October, in collaboration with Seattle Public Utilities and Dr. Andrew Bryan at UW Medicine.
At the pump station, they have installed an autosampler, which allows water to trickle into a sampling container slowly over the course of an hour.
Once the sewage sample is collected, they prepare the effluent — the liquid waste — and then identify the presence of COVID-19 RNA.
“The method that we use to detect SARS-CoV-2 is exactly the same method that is used to detect the virus if you take a swab,” Winkler said. “The PCR, the primers, everything — it's the same.”
To estimate the number of people that each sample represents, they look at the total amount of waste present by quantifying the amount of waste-related compounds (ammonia and phosphorus). The PCR data, in addition to the population size estimate, allows them to approximate the percent of the community with COVID-19.
They verified their methods using a manhole near UW’s Greek Row and a pump station near University Village. They chose the manhole that contained sewage from Greek Row to be close to a positive control, because during the fall, sororities and fraternities were sites of significant COVID-19 outbreaks.
They now have moved their pump station test to the Mount Baker neighborhood, with the hope of being able to sample a mixed-income community with more essential workers.
Although testing sewage for COVID-19 does not provide an absolute number of infected individuals, it can identify trends and outbreaks. In addition, this type of testing is anonymous and extraordinarily cost-effective.
“Think of one sewer shed where you test every person in that sewer shed every day once, or you take a sewer sample and sample the entire population with one test,” Winkler said.
Winkler refers to pump-station sampling as a smoke detector that can show us “where the fire is burning,” and potentially guide the rollout of resources and vaccines.
Although right now there is only one pump being sampled in Seattle, Winkler believes that with institutional support, pump-station sampling could be used to map COVID-19 throughout the entire city.
Reach contributing writer Nuria Alina Chandra at email@example.com. Twitter: @AlinaChandra
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