What You Should Know About the CDC's Wastewater COVID Testing Program

As Omicron rates drop in the U.S. and states begin to rescind mask mandates, public health experts are figuring out how best to stay vigilant for any new outbreaks and variants of COVID-19. 

One way is through surveillance of wastewater in communities. The Centers for Disease Control and Prevention (CDC) announced recently that the agency is expanding nationwide efforts to detect COVID-19 outbreaks as early as possible by checking community wastewater for the virus.

The CDC made the announcement in a teleconference with reporters on February 4, 2022.

“Estimates suggest between 40% and 80% of people with COVID-19 shed viral RNA in their feces, making wastewater and sewage an important opportunity for monitoring the spread of infection,” said Amy Kirby, PhD, MPH, team lead for the National Wastewater Surveillance System at CDC, during the call.

The wastewater is collected by utility workers and then evaluated at state and CDC laboratories. 

While the CDC began the National Wastewater Surveillance System (NWSS) in September 2020 at hundreds of sites, it is only now adding wastewater surveillance data to the agency's COVID Data Tracker site, so people can see trends in their communities, Kirby said.

“The real power of this program will be more evident in the coming weeks when hundreds more testing sites…begin submitting data,” Kirby said. “Because increases in wastewater generally occur before corresponding increases in clinical cases, wastewater surveillance serves as an early warning system for the emergence of COVID-19 in a community.”

Kirby told reporters that people who have COVID-19 generally shed high levels of the virus in feces very early in their infections, but shed much less as the infection progresses. Infections are captured even in people without symptoms, which is what makes the wastewater surveillance such a valuable tool. 

How Wastewater Testing Improves the COVID Response

A key reason why wastewater surveillance is especially important now is that people are increasingly turning to home kits to test for COVID-19. Their results are generally not reported to state labs, so community levels of COVID-19 may appear lower than they actually are.

Wastewater testing also helps public officials know where to allocate resources. If COVID-19 is present in a given site, public health experts have a better idea of where to send mobile testing and vaccination sites.

“We use the information to decide where we're going to prioritize interventions in certain parts of the city where the wastewater data tells us infection rates are higher,” Loren Hopkins, PhD, chief environmental science officer for the Houston Health Department, told Verywell.

“The pattern is that you see an increase first in the wastewater, then in the positivity rate (of COVID tests), and then in hospitalization rates," she said. "So, wastewater testing is a bellwether to what's happening."

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.