While COVID-19 cases are decreasing nationwide, health officials are still carefully monitoring cases in case they see unexpected spikes or a new variant makes an appearance.
But relying solely on PCR or rapid COVID-19 test results can be imperfect if people don’t get tested or if they’re unable to report results of at-home tests. One way to counteract this is by looking at wastewater for an area.
COVID-19 can be identified in wastewater up to 2 weeks before they’re being detected in clinical samples from the same area, according to the Food and Drug Administration (FDA).
Now the Centers for Disease Control and Prevention (CDC) has created an interactive map to show where COVID-19 is being detected in wastewater in the United States. They also announced they’re increasing their efforts to collect wastewater samples from communities nationwide to identify traces of the pandemic virus.
“Because increases in wastewater generally occur before corresponding increases in clinical cases, wastewater surveillance serves as an early warning system for the emergence of COVID-19 in a community,” said Amy Kirby, PhD, who leads the CDC’s National Wastewater Surveillance program, during a media telebriefing.
Wastewater is essentially a community’s sewage. It’s what ends up being flushed from our toilets and down our drains.
Benjamin Kopek, PhD, associate professor of biology at Hope College in Michigan, told Healthline that the process begins with the collection of wastewater samples.
“The samples are then processed to extract nucleic acids, this can be done using multiple different methods,” he said.
Kopek explained that a test very similar to the conventional PCR test is then done using a probe to detect COVID-19.
“Although SARS-CoV2 may replicate in intestinal cells, it’s more likely going to end up in feces because mucus/saliva containing the virus are swallowed and then follow the digestive tract,” he noted.
The new CDC map shows the changing levels of the coronavirus’ genetic material in wastewater at different sites over the previous 15 days.
A site that doesn’t detect coronavirus after conducting at least one test during that period will be logged as a “non-detect.”
If no samples are collected during that time, it will be labeled as “no recent data.”
In the coming weeks, hundreds of sites will begin submitting data that will be displayed on the tracking website, Kirby said during the briefing.
She explained that the data could be somewhat limited because there are still areas without the needed infrastructure to do this type of testing.
According to Zuzana Bohrerova, PhD, a research specialist in the Department of Civil, Environmental, and Geodetic Engineering at Ohio State University and associate director of the Ohio Water Resources Center, not all coronavirus enters wastewater through urine and feces.
“Additionally, the virus ends up in the wastewater from spit and skin during brushing teeth and washing,” she said.
Bohrerova pointed out that most of the virus that ends up in wastewater is degraded, so only the “genetic signal” (RNA) of the virus is monitored.
The virus RNA is diluted in wastewater, she said, because wastewater also contains dishwasher water, shower water, and other “industrial” wastewaters. Therefore, tracking includes methods that concentrate it.
Bohrerova emphasized that wastewater surveillance is more than an early warning system.
“It can also help to target vaccination, testing, contact tracing, and other resources,” she said. “It provides information about the whole community and not only individuals.”
Bohrerova emphasized that wastewater testing can provide information on COVID-19 levels within a community even when clinical testing is unavailable or infected individuals aren’t seeking testing.
“It could also be used at a building level, such as congregate living facilities, to inform a testing strategy,” she noted. “This was done at Hope College in 2020 to 2021.”
Asked about the reliability and accuracy of this kind of detection system, Bohrerova said it’s possible to detect a single infected individual in a population of hundreds, if not thousands.
“However, there are multiple factors that influence detection beyond the laboratory methods, such as frequency of bowel movements,” she said.
Aaron Peacock, PhD, director of the Microbac Laboratories, Inc. molecular biology laboratory in Oak Ridge, Tennessee, said that tracking COVID-19 in wastewater can mean identifying potentially dangerous variants more quickly.
“Some of these variants have mutations that make them more transmissible, even with vaccinations,” he cautioned. “The information provided by wastewater testing can monitor the virus as a whole and its variants.”
Peacock said this wastewater data is probably most useful when combined with case-based testing.
“The wastewater data can provide information on those with active infections but no symptoms,” he said. “This provides a background or baseline for the infection rate in a community.”
Dr. David P. Calfee, editor of the journal Infection Control & Hospital Epidemiology and professor of medicine and population health sciences at Weill Cornell Medicine, said that by getting earlier information about disease prevalence from wastewater, we might know of disease spikes up to a week ahead of time, before we see increases in the number of people testing positive.
“You can use that information to make some important decisions about preparedness, distribution of resources,” he said. “If you start to see increases in your wastewater surveillance, you may want to start ramping up your diagnostic testing capacity in your community.”
Calfee added that this information helps at both the individual and community level, especially for community or personal prevention strategies like mask use and reconsidering social gatherings and events.
The CDC has announced a wastewater surveillance program that will track community COVID-19 levels by analyzing local sewer systems.
Experts say this method of virus detection is accurate enough to detect a single infected individual.
They also say that the information can be used to more effectively allocate vaccination, testing, contact tracing, and other resources.
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