The Centers for Disease Control and Prevention will publish data from wastewater surveillance as a tool to measure the amount of COVID-19 circulating.
More than 400 sites across 19 states will begin submitting findings to the CDC this week, and another 250 sites will come online in the coming weeks. The agency said it will begin publishing data collected as part of its National Wastewater Surveillance System on the COVID-19 dashboard for the first time.
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“Wastewater surveillance offers public health officials a better understanding of COVID-19 trends and communities because increases in wastewater generally occur before corresponding increases in clinical cases,” said Amy Kirby, team lead for the CDC’s National Wastewater Surveillance System.
Sewage surveillance has been used for decades to monitor for polio outbreaks and, more recently, the presence of illicit drugs in communities. The pandemic has brought this little-discussed public health tool to the forefront.
Researchers at the CDC have reported that roughly 40% to 80% of people infected with the coronavirus shed virus RNA in their stool. When the virus infects the human body and begins furiously replicating itself, some of those replicated pathogens are shed to the intestines and passed. After collecting samples, utility operators at sewage treatment sites send them to a laboratory, where scientists concentrate the virus out of that wastewater sample. Evidence of the virus is detected using the same testing technology used for PCR tests, in which a swab is used to collect a sample from the nose.
Tracking the presence of the coronavirus in wastewater reveals epidemiological blind spots caused by sporadic home testing and lack of reporting if no symptoms are present. The practice can offer clues about the possible next variant, or variants, of concern. As omicron recedes, officials hope that monitoring sewage will help prepare cities for future outbreaks.
“The role of wastewater surveillance will largely be around that early warning system to detect increasing cases as soon as we can so that we can have those extra days for communities to prepare their hospital systems for the pending cases,” Kirby said.
Wastewater surveillance was instrumental in detecting the first cases in the U.S. of the highly transmissible omicron variant, which overtook the delta variant in about a month. In Colorado, for instance, the state Department of Public Health and Environment uses sequencing to conduct biweekly tests of wastewater across 21 sewersheds, or the area of land where all the sewers flow to a single endpoint. Health officials detected 13 omicron-associated mutations in a sample collected on Dec. 2. At that time, only one travel-related omicron case had been reported in Colorado. Two weeks later, omicron was detected at 19 of 21 sewersheds.
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There are limits to the advantages of wastewater surveillance. Sampling in tourism destinations can provide unreliable data due to the transient population. The surveillance system also does not reach homes that are not connected to sewers but instead use septic systems, most common in rural areas. Still, just about a quarter of homes in the U.S. rely on septic systems, making this surveillance option attractive for wide-scale use to detect infectious diseases in addition to COVID-19.
“Once we have built the infrastructure to collect the samples, give them to a laboratory, get the data to CDC, we can add tests for new pathogens fairly quickly,” Kirby said. “Should there be a new pathogen of interest, we could ramp up the system within a few weeks to start gathering community-level data on that pathogen.”
