New Pandemic Hero: Sewage

New Haveners, take heart: our poop indicates that citywide Covid-19 infections are stable, at least for now.

That message came Thursday from an expert who has been studying the city’s sewage to help officials get out in front of the spread of Covid-19.

“The sewage facilities measure primary sludge every day, and send us results three times a week,” said Yale engineering professor Jordan Peccia. (Primary sludge is wastewater solid that’s separated by settling to the bottom.)

Peccia spoke about the Covid-19 poop-analysis Wednesday on Connecticut Public Radio’s ​“Where We Live” program hosted by Lucy Nalpathanchil. They were joined by Yale doc and gubernatorial Covid-19 adviser Albert Ko and Stamford Mayor David Martin, whose city is also working with Peccia’s team. After the show, Peccia spoke to the New Haven Independent in a separate interview.

Why Sewage

Measuring wastewater was initially used to fight polio. As infected people could be asymptomatic or have mild symptoms, fecal samples helped pinpoint hidden polio outbreaks.

Peccia wanted to try the same strategy with Covid-19.

“Covid is part of a class of pathogens that infect different tissues in the body,” he said. ​“Although it’s often in the lungs, it can also be present in the gut, meaning we can detect Covid samples through sewage.”

Peccia and his team of three began measuring fecal samples on March 19t, starting with New Haven’s sewage facility. Although the facility serves over 200,000 people, Peccia was able to pinpoint new COVID cases on a granular level.

“We collect 40 mililiter samples each day, and use the same techniques as a nasal swab test,” he said. His team then measures the concentration of virus strands to determine new cases.

“If there’s 1,000 virus strands per milliliter, then we know there’s at least one person infected per 100,000 people,” explained Peccia.

His team can’t always find single cases, ​“but if there are three or four, we’ll detect it pretty quickly,” he said. And since it takes about 15 hours for sewage to go from being flushed to being tested, the samples can be mapped to real time.

Over several months, Peccia began to notice an interesting pattern. When his team mapped their sample results to reported cases of COVID, they saw that the samples mirrored the peaks and falls of reported cases. However, the samples indicated those peaks and falls about seven to ten days earlier.

In other words, data from wastewater became ​“the proverbial smoking gun,” said Dr. Ko.

This is fundamentally different, he said, from ​“lagging metrics such as hospitalizations and deaths.” By its very nature, lagging data meant that the ​“community transmission had probably occurred weeks before.” While lagging data could help in the future, it couldn’t do much about current outbreaks.

“Waste is unique,” said Ko, ​“because it can help us identity outbreaks and transmissions ahead of time, allowing us to respond preemptively.”

To help others across Connecticut, Peccia’s team expanded to surveying five other cities: Hartford, Bridgeport, Stamford, Norwich and New London, reaching approximately one million people.

How Cities Use The Data

Stamford took interest in this new tool early on, said Mayor Martin. In March and April, testing was not nearly frequent nor fast enough to track the spread. And as he crafted Stamford’s response to the pandemic, this seemed like ​“the perfect early warning indicator.”

“I have a degree in biology,” Martin said. ​“So this made a lot of sense to me.”

Using sewage samples could provide crucial information for cities with vulnerable populations. ​“Targeting waste in cities is very smart, where transmission risks are high” said Ko.

Martin was similarly concerned about Stamford’s low income neighborhoods, which have dense high-rise housing.

There isn’t a precise bright line where the number cases becomes concerning, said Peccia. ​“We don’t have enough data quite yet to develop a formal statistical analysis. So we just analyze graphs and their trends.”

Although rudimentary, this data has already saved lives. ​“One day, we got an email at 1:30 saying that our sewage had higher Covid levels and we needed to pay attention,” Martin said. ​“By 4:30, we sent out a letter to communities and warned them of this early increase.” The samples were correct: In ten days, Stamford saw the predicted increase of cases, although levels dropped quickly again.

“I think we got it under control because communities took the warning to heart,” said Martin. ​“It was a good reminder, especially since people have pandemic fatigue.”

In New Haven, waste samples have yet to find a concerning increase in cases. 

“We communicate with Mayor [Justin] Elicker and Director of Health Maritza Bond at least once a week,” Peccia said. Public reports are also published for the community on Mondays, Tuesdays, Thursdays, and Fridays. Last week’s public sample report can be found here.

“It’s no guarantee, but New Haven’s data has been relatively calm this last week,” said Peccia. ​“We’re making progress.”

Peccia’s research on waste samples, published by the journal Nature Biotechnology, can be found here.