COVID-19 clues in a community’s sewage: 4 questions answered about watching wastewater for coronavirus
"How do you monitor wastewater for germs?
The overall concept is pretty straightforward. Infected individuals excrete the pathogen, which gets flushed down the toilet or washed down the drain. The pathogen – or fragments of its genes – then travel through a community’s sewage system to a treatment plant, where careful sampling can detect its presence.
About two-thirds of people infected with SARS-CoV-2 excrete the coronavirus in their stool. A treatment facility can monitor wastewater for the virus’ RNA using molecular tools.
There’s no real standard yet, but most approaches involve concentrating the wastewater sample to some degree to make it more likely that you’ll be able to detect any RNA. We’re not looking for a whole, intact genome, but a small sequence of a single SARS-CoV-2 gene.
The RNA fragments that we’re measuring are too small to physically capture directly. So we use other tricks to snag them, usually by what we call electrostatic interaction – getting the RNA to stick to something like a filter, or using other chemicals to get it to clump together.
Then we quantify how much of the viral RNA is in the sample.
It’s important to recognize that we can’t directly extrapolate from what’s measured in the wastewater to how many people in the community have the coronavirus – at least not yet."
Header photo: Millions of households’ wastewater can flow to one treatment plant. Nicholas Kamm/AFP via Getty Images