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Throughout much of the pandemic, public health experts have used an unlikely tool in the fight against COVID-19: the sewer system.

In fall 2020, the Centers for Disease Control and Prevention (CDC) launched the National Wastewater Surveillance System. Many health departments in the U.S. take part in this program. They monitor wastewater (sewage) for the virus that causes COVID-19. Wastewater tracking can alert them to an uptick in local infections even before a lot more people start to test positive for COVID-19.

How it works

People who have COVID-19 (even if they don't feel sick) can shed the virus in their feces. The virus enters the sewer system when people flush their toilets. It then goes through sewer pipes to the local treatment plant, where it is sampled before it is treated. A lab tests the samples and measures the amount of virus in the wastewater. The results are shared with health departments.

An early warning

If the amount of virus found in a wastewater system goes up over time, it may be a sign that COVID-19 is on the rise in the area. Testing sewage also helps show when cases of the virus go down.

Knowing this can give health officials time to respond. It can help them make decisions about how best to reduce the spread of the virus. For instance, they might set up testing sites or vaccine clinics.

A strength of this method is that it can detect when the virus is gaining ground even among people who do not have symptoms. And it can be used to track new variants of the virus.

What's more, wastewater sampling can also be used to detect other diseases, like polio.

Stay in the know

Wondering what your community's wastewater says about the current levels of COVID-19? View a CDC map of virus levels found in wastewater. Want more COVID-19 news? Check out our Coronavirus health topic center.

Reviewed 2/3/23