Monitoring Poop for Covid-19

For the past two years, scientists across the country have been performing a gross—but important—job to keep tabs on Covid-19. They’ve been visiting sewage treatment plants in major cities across the United States to search for evidence of SARS-CoV-2. This virus, which causes Covid-19, can be found in the poop of people who have the disease. That makes sewage treatment plants ideal places to monitor Covid-19 infections in an area.

Wastewater monitoring has become an important tool during the pandemic. “It gives us a picture of the status of health within a community, from a college campus to the entire city of San Francisco.” says Laura Roldan-Hernandez, a member of the Sewer Coronavirus Alert Network, which monitors sewage plants in California.

The sewage that ends up at a treatment plant comes not only from toilets, but also dishwashers, sinks, showers, and washing machines, as well as runoff from stormwater and industry. But “the vast majority of wastewater is human feces,” says Amy Kirby. She’s a program lead for the National Wastewater Surveillance System at the Centers for Disease Control and Prevention (CDC). 

At a sewage treatment plant, wastewater is pumped into large tanks. Poop and other solids separate from the liquid, sinking to the bottom of the tanks to form sludge. “It’s dark brown or black with the texture of oatmeal,” says Roldan-Hernandez.

Roldan-Hernandez and other scientists collect samples of this dark, oily substance to test for the presence of SARS-CoV-2. In a lab, they run a polymerase chain reaction (PCR) on the sludge samples. If the virus is present, this test makes millions of copies of its genetic material so it can be easily detected. The same test is used to detect the virus on nasal swabs taken from people (see Why Covid-19 Testing Matters).