Follow the sewage.
The Centers for Disease Control and Prevention said Friday that it will expand efforts to collect wastewater samples from communities across the country to search for traces of the coronavirus. The agency said monitoring for viral particles in sewage provides an important, on-the-ground snapshot of how the virus is spreading.
Known as wastewater surveillance, this type of research has emerged as a key way to assess the health of communities beyond traditional Covid-19 testing, particularly in neighborhoods with unequal or limited access to health care, such as minority and low-income communities.
Amy Kirby, the program lead for the CDC's National Wastewater Surveillance System, said between 40 percent and 80 percent of people with Covid shed bits of the virus in their feces. This includes people who are asymptomatic, which means wastewater surveillance can detect the virus in stool samples from people who may not have even known they were positive for Covid, she said.
As such, studying wastewater can reveal how pervasive the virus is at the local level and can provide a heads-up to public health departments about where new outbreaks may be occurring.
"Because increases in wastewater generally occurred before corresponding increases in clinical cases, wastewater surveillance serves as an early warning system for the emergence of Covid-19 in a community," Kirby said.
Knowing which areas have high concentrations of the virus could help public health departments plan for how to deal with surges of infection, including where to open more testing and vaccination sites and how best to direct hospital resources.
Jordan Peccia, a professor of chemical and environmental engineering at Yale University, has been collecting daily wastewater samples in New Haven, Connecticut, and its surrounding areas. He said this has allowed him and his colleagues to track the evolution of local outbreaks and follow the emergence of variants such as delta and omicron.
"It's always good to get out ahead of any type of outbreak, and wastewater typically gives you a few days in advance of what the testing apparatus does," he said.
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Peccia added that wastewater surveillance will continue to be an important tool as the pandemic progresses, particularly as widespread testing winds down between waves of infection or when the virus becomes endemic, circulating indefinitely but at much lower, easier-to-manage levels.
The National Wastewater Surveillance System currently collects daily samples from more than 400 sites across 37 states and two territories, according to the CDC. The agency expects to add 250 additional sites to the register in the coming weeks. The system won't represent the entire country, but Kirby said, "we will have a look into most states, as well as territories and tribal communities."
Wastewater surveillance data will be added to the CDC's national Covid tracker. The dashboard will display changes in virus levels found in wastewater over the previous 15 days for each participating community, and will also indicate the percentage of tests in these areas that were positive over the past 15 days.
Wastewater surveillance for Covid began in September 2020, largely as a grassroots initiative led by individual teams of scientists. Since then, Kirby said, more than 34,000 samples have been collected, representing roughly 53 million Americans.
