Researchers at Yale University found that testing “sewer sludge” in wastewater for coronavirus could detect an outbreak more than a week earlier than traditional contact tracing.
In the study, published last week in the journal Nature Biotechnology, researchers began taking daily samples from a New Haven-area wastewater treatment plant, which serves multiple towns in Connecticut including New Haven, East Haven, Hamden and parts of Woodbridge.
The study’s results, which span 10 weeks from March 19 to June 1, found that testing sewers for Covid-19 — collecting samples from the “primary sewage sludge” of settled solids — produces transmission trends that are “very similar” to those of contact tracing, but come about “six to eight” days earlier.
Wastewater testing is exactly as it sounds — and it isn’t anything new.
The science of studying human fecal waste as a way of predicting a population’s risk for viral spread, also known as wastewater epidemiology, has been successfully used by the global community in the fight against polio.
Wastewater, or sewage from households or buildings, can harbor viruses like coronavirus regardless of whether a person is symptomatic. When scientists extract human waste from municipal sewage systems, then analyze it for dead virus particles, they’re given clear indication of the number of infected individuals in that area.
“In communities where test reporting is delayed,” the researchers wrote, “sludge results, if analyzed and reported on the same day as sampling, can provide substantial advance notice of infection dynamics.”
This roughly week-long period can be crucial to curbing coronavirus outbreaks. According to the Centers for Disease Control and Prevention, those infected with the coronavirus may not show symptoms for up to 14 days, if at all, but may otherwise be contagious.
In August, the University of Arizona claimed a campus outbreak was averted in part because of wastewater testing which indicated two asymptomatic students were in a campus dorm. Prior to students, faculty and staff returning to its campus, the university had enacted a campus-wide initiative in which campus sewage systems were actively monitored for traces of coronavirus.
In countries like The Netherlands, France, and Australia small pilot studies have also demonstrated the promise wastewater testing.
In Paris, researchers released findings in April showing they’d successfully mimicked the rise-and-fall curve of the city’s on-the-ground epidemic over a 1-month period of testing the city’s sewage systems.
The Yale study also says wastewater testing is less costly, intricate and time consuming than contact tracing. As such, it benefits low-income communities and communities with overwhelmed public health systems where there are lags in testing.
But the researchers cautioned wastewater testing for Covid-19 is still “poorly understood”.
“There’s still a lot more to do,” researcher Jordan Peccia, a professor at the Yale School of Engineering and Applied Science, told NBC News. “We’re one of the earlier groups to have developed a robust relationship between wastewater and coronavirus cases, but this is just a first step.”
“It doesn’t replace contact tracing,” Peccia said. “(But) if we know a little bit ahead of time, we can raise the alarm.”