Department of Environmental Protection microbiologist Alexander Clare helps test wastewater samples for the coronavirus inside at a lab at the Newtown Creek facility in Brooklyn, Dec. 3, 2020. Ben Fractenberg/THE CITY

Three years into the pandemic, low testing rates and spotty case reporting are making it harder to know how widespread COVID is in New York City at any given moment.

Hospitalization rates remain a useful indicator, but by the time a flood of patients are admitted to the hospital for COVID, the virus has already spread.

To get an early warning sign that COVID is surging, health officials have turned to wastewater data — and THE CITY is adding this new tool to our Coronavirus in New York City tracker.

So, how does wastewater monitoring work?

Twice a week, city officials measure the concentration of COVID genetic material in our sewer systems. They then report their findings to the public once a month, and health experts use trends in this data to estimate changes in COVID cases.

Jumps in wastewater concentration can signal a rise in COVID even before reported cases.

Beyond looking at changes over time to detect a surge in cases, New Yorkers can also see COVID levels in wastewater within the 14 water treatment plant watersheds where scientists draw samples in the five boroughs.

THE CITY talked with public health experts and scientists to break down all of the details about how wastewater detection works, how to interpret the data, and how it could affect your day-to-day decisions.

What does wastewater have to do with COVID anyway?

Simply put: when someone has COVID, they shed the virus through their poop just as they do through a sneeze or a cough. The virus then gets flushed down toilets and accumulates in the sewer system — and scientists can then measure the concentrations of COVID in wastewater to estimate the prevalence of COVID in that given area.

How is wastewater tested, and who’s sampling the sewage?

Before wastewater is treated, the city’s Department of Environmental Protection takes biweekly water samples from all 14 wastewater treatment plants across the city and sends them to the NYC Department of Health.

After that, scientists run laboratory tests on the samples, analyze the resulting data, and run the data through some checks before publishing it to the public each month, a state Dept. of Health official told THE CITY. The state maintains a wastewater surveillance dashboard, which shows COVID detection levels across the state, including data provided to them by New York City.

How good is wastewater monitoring at detecting COVID?

“Wastewater is an excellent indicator,” says Queensboro Community College professor Monica Trujillo, coprincipal investigator for the Wastewater Epidemiology Training Laboratory (WETLAB) at Queens College, which has experimented with wastewater surveillance systems since the early days of the COVID pandemic.

Now that COVID testing and reported case data are less reliable, wastewater surveillance “makes a lot of sense because you are detecting the asymptomatic,” says Trujillo, “ [you are] looking at everybody who uses the toilet.”

However, experts agree that wastewater data should always be interpreted as one of many indicators measuring COVID, alongside statistics measuring hospitalizations and vaccinations.

“We should always use multiple data sources to understand infectious disease transmission,” Prof. Dave Larsen from the Public Health Department at Syracuse University told THE CITY.

What should I be looking for in COVID wastewater levels?

“When you see a 5% increase from one week to the next … it’s a real uptick” says Trujillo. “That doesn’t mean necessarily that hospitalizations are going to go up, but it does tell you that there are going to be more cases.”

Many experts affirmed that the actual level of COVID genetic material in wastewater is less important to know than how this level changes over time.

“The day-to-day data doesn’t mean anything. What you need is the trend,” says Trujillo.

What is a sewershed area? Is that the same thing as a neighborhood, or borough?

A sewershed is an area of the city where everyone’s waste goes to the same place, a shared wastewater treatment plant. New York’s 14 sewersheds cover massive swaths of the city and represent hundreds of thousands of peoples’ waste, so data for a given sewershed doesn’t actually help you understand your individual COVID risk or even that of your neighborhood.

That being said, geographic trends in wastewater data can help show differences across boroughs, which historically has provided important information at key points during the pandemic.

“Staten Island was the one borough where there was more resistance to the vaccine. And wastewater rates were higher,” offered Trujillo, as an example.

Can we see any more granular data, from a smaller sewage area?

As of now, no. Since the city takes wastewater samples at each treatment plant, those samples represent waste from that entire sewershed, and there’s no way to further break down where the waste came from.

However, scientists can conduct surveillance in any wastewater system. Trujillo’s WETLAB is currently testing wastewater for COVID in NYC Health and Hospital locations, estimating COVID cases among the patients, staff, and visitors who use the toilets in the city’s public hospital.

If researchers are looking at all of our waste, are they collecting or looking at my genetic information?

Identifying an individual’s DNA or COVID status from NYC wastewater is scientifically impossible.

“There are a lot of people who are very concerned about this privacy issue… saying that it’s a way for the government to spy on you,” says Trujillo, “but the way the wastewater analysis is done, you have no way of knowing who is shedding.”

Trujillo points out that within sewersheds, “everything goes into the same pool” as the waste of hundreds of thousands of New Yorkers end up mixed together in one wastewater sample.

How much longer will this data be available?

Both the city and state’s Department of Health will continue their wastewater surveillance program without plans to end it anytime soon.

However, Trujillo says that more funding for research, and more personnel support to aid in the sample collection and testing process, will make this vital COVID detection practice stronger.

“Wastewater surveillance is here to stay,” says Trujillo, “and we need people trained for it.”

This story was published by THE CITY on September 26, 2023.