(NEXSTAR) – For years, the Centers for Disease Control and Prevention (CDC) have been tracking various health metrics across the U.S. Among the newest is poop, which is being surveyed to keep an eye on the prevalence of COVID-19.

Scientifically speaking, the CDC is surveilling wastewater in dozens of communities, primarily in the Midwest and New England. In September 2020, the CDC launched the National Wastewater Surveillance System (NWSS), which works with local health departments to track SARS-CoV-2.

By using data from the wastewater testing areas, health officials can better, and more quickly, respond to the spread of COVID-19. During a Feb. 4 telebriefing, Dr. Amy Kirby, team lead for the NWSS, noted that the surveillance system has collected more than 34,000 samples representing roughly 53 million Americans.

How it works

According to the CDC, people who become infected with SARS-CoV-2, the virus that causes COVID-19, can shed the genetic material of the virus in their feces. That genetic material, or RNA, can then be detected in wastewater, which includes water from toilets, showers, and sinks.

Sewage from participating sewer sheds – the area served by a wastewater collection system – is collected as it flows into a treatment plant. Samples are sent to environmental or public health facilities to be tested for SARS-CoV-2. Health departments then submit testing data to the CDC where it is analyzed to evaluate the presence of COVID in the community.

By measuring SARS-CoV-2 levels in wastewater over time, the CDC says public health officials can determine if infections are increasing or decreasing within their community.

Wastewater surveillance isn’t new, either – according to Kirby, officials overseas have conducted similar efforts to eradicate polio.

Where wastewater is being tested

Communities in Texas, Illinois, Michigan, California, and Oregon are among those conducting wastewater testing. Other participating states include Wisconsin, Ohio, Missouri, New York, Virginia, and North Carolina.

The CDC is currently supporting 34 states, four cities, and two territories to develop wastewater surveillance systems while more than 400 sites have already begun their work. In early February, Kirby said the NWWS has a commercial testing contract that will provide twice-weekly testing to an additional 500 sites.

Testing of wastewater isn’t able to capture data from every home or major facility, according to the CDC. Homes that rely on a septic tank, for example, are not captured in the community-level surveillance. Neither are prisons, universities, or hospitals that treat their own waste.

Wastewater treatment plants that pre-treat the sewage before it reaches the plant are also unavailable surveillance sites.

Where to see the data

While wastewater surveillance has been happening since early in the pandemic, the CDC just recently made the data it has been collecting available to the public. If wastewater surveillance is happening in your community, your local health department likely has a publicly-accessible dashboard as well.

Regarding the national data, the CDC uses a color-coded chart to show the 15-day percent change in the levels of SARS-CoV-2 found in surveyed wastewater. Those who have seen a decreased change in SARS-CoV-2 prevalence appear blue while those seeing increased change are shades of orange or red. Communities marked with a gray dot have no recent data available.

As of Feb. 17, most of the communities reporting wastewater surveillance data are noted with blue dots, meaning a decline in SARS-CoV-2 has been detected.

On the CDC’s map, you can also review the 15-day detection proportion within participating communities. According to the CDC, this is calculated over a 15-day window by dividing the number of tests in which SARS-CoV-2 was detected by the total number of tests for all sampled sewer sheds.

What’s next?

As seen on the CDC’s map, not every state is conducting wastewater surveillance. Kirby explained earlier this month that the agency is working to add more testing sites in the coming weeks.

Outside of COVID, Kirby noted that they are working to expand NWWS to gather data on other pathogens, saying, “our targets include antibiotic resistance, foodborne infections, like E. Coli, salmonella, norovirus influenza and the emerging fungal pathogen, Candia Auris.”

She explained that once the infrastructure is in place to collect samples, submit them to a laboratory, and share data with the CDC, adding tests for other pathogens can be done “fairly quickly.” Further still, wastewater surveillance could be used for non-infectious diseases, like substance abuse.

According to Kirby, this kind of surveillance “needs more technical analysis and technical development.”