As the city moves through the phases of reopening, data is key. Public officials are closely tracking COVID-19 test results, hospital admissions, fatalities and other indicators to ensure there isn’t another spike in cases. Soon, they may have another trove of data at their disposal: the sewers.

The coronavirus can show up in a person’s feces even if they’re not yet experiencing symptoms of the disease, making sewage surveillance a promising tool for sussing out a burgeoning coronavirus hotspot. The process of developing a sewage surveillance system for the disease is complicated, though. The city’s Department of Environmental Protection has been working with researchers from the NYU Tandon School of Engineering and other institutions for months to hone its methodology for testing the levels of genetic material associated with coronavirus that are present in the city’s wastewater.

DEP began collecting wastewater samples in April and is now ready to start analyzing them at its microbiology lab at the Newtown Creek Wastewater Resource Recovery Facility in Brooklyn.

“Our expectation is that by the end of July we will have a rather consistent data stream,” Dimitri Katehis, DEP’s director of regulatory compliance and innovation, told Gothamist. “Our goal is really to provide support should there be a resurgence of the virus in the fall, which is what the unfortunate expectation is, based on what we’ve been seeing elsewhere.”

DEP aims to trace any spike in the levels of COVID-19 in the wastewater back to the neighborhood it came from so that public health officials can then deploy targeted interventions to contain the spread.

The method has already shown promise elsewhere in the U.S. For example, in Utah, wastewater indicated an outbreak in the areas surrounding a meatpacking plant where 287 workers had been infected with the virus several days before it was officially reported.

Wastewater surveillance has been used in the past to track other viruses and bacteria — most notably to detect the presence of polio in the few countries where it still sporadically resurfaces. Now, researchers are scrambling to develop and standardize methods for using it to track COVID-19.

Because this particular virus breaks down easily in sewage, it’s more difficult to test for than “far hardier pathogens” such as norovirus or polio, said Katehis.

The amount of rain New York gets and the fact that stormwater mixes with wastewater also poses a challenge. “That dilutes the level of the virus that’s present in the wastewater streams, making it harder to enumerate,” Katehis said. He added that DEP has had to adapt testing methodology developed at Stanford in the dry clime of California to New York City’s climate and infrastructure.

Researchers from NYU and other institutions across the country have received a $250,000 grant from the Alfred P. Sloan Foundation to develop a blueprint for municipalities to implement their own wastewater surveillance systems, which will be based in part on the lessons learned in New York. They aim to offer guidance on best practices for collecting and analyzing samples and for efficiently communicating information to public health officials and policymakers.

“By implementing these monitoring techniques, the NYC DEP and other wastewater utilities can complement other forms of testing traditionally used for disease surveillance–not just for the ongoing COVID-19 pandemic,” Andrea Silverman, an assistant professor of civil and urban engineering at NYU Tandon who is working with the DEP, said in a statement on the project.

Katehis says wastewater surveillance could potentially be used in the future to track seasonal flu levels or outbreaks of other diseases.

“I don’t want to be a pessimist here but we do anticipate there will be more like this,” he said, referring to other pathogens that could threaten to cause a pandemic. “And we will have one more tool at our disposal to be able to identify it as early as possible and be able to support [the city Health Department] in making the tough calls that they’ll need to make.”