For the past 18 months, the Centers for Disease Control and Prevention (CDC) has been collecting data on the levels of SARS-CoV-2 RNA in more than 400 sites around the country as a way to track the spread of COVID-19 in different communities. On February 4, the agency announced that it’s now sharing that information in a dashboard as part of the COVID Data Tracker. “Wastewater surveillance can help provide situational awareness for what’s going on in a community, as well as an early-warning system that a new increase may be coming to an area,” says Amesh A. Adalja, MD, a senior scholar at the Johns Hopkins Center for Health Security in Baltimore who is not himself involved in wastewater surveillance. Surveillance testing is different from diagnostic testing or screening tests. Rather than identifying current infections in individuals, surveillance testing can monitor community or population-level outbreaks of COVID-19, according to the CDC. The virus levels found in wastewater surveillance can’t be traced to specific individuals, but they can signal an increased need for diagnostic or screening tests in a certain area.
People Infected With COVID-19 May Shed the Virus in Their Feces
It’s estimated that between 40 and 80 percent of people with COVID-19 shed viral RNA in their feces, which makes wastewater and sewage an important opportunity for monitoring the spread of infection, said Amy Kirby, PhD, MPH, the team leader of the National Wastewater Surveillance System, in a CDC Telebriefing on February 4. Shedding of COVID-19 in feces starts very soon after a person is infected, said Dr. Kirby. “It’s in fact one of the first signs that we see of infection, which is really important for this early warning capability for wastewater,” she said. A lot of the virus is shed very early in the infection and then tails off; it continues until a couple of weeks after infection but at a low rate that doesn’t significantly impact the level, said Kirby.
The University of California in San Diego Used Wastewater Data to Limit the Spread of COVID-19 on Campus
Although the surveillance was launched 18 months ago, “the real power of this program will be more evident in the coming weeks, when hundreds more testing sites will begin submitting data,” said Kirby. The agency expects to add “at least” an additional 250 sites in the near future, which will allow a look at most states as well as territories and tribal communities, she said. Because the virus is shed in feces so early in the infection, communities will get a “heads-up” that will allow them a few extra days to prepare, which can “really make a difference on the ultimate trajectory of that surge in your community,” said Kirby. Wastewater surveillance has already been used successfully to help communities prepare for COVID-19. Researchers at the University of California in San Diego School of Medicine began screening wastewater from campus buildings for signs of the virus in the summer of 2020 as a way to prevent outbreaks, according to a university release. A team of researchers found that they could detect even a single infected asymptomatic person living or working in a large building. When they notified occupants about the presence of the virus, COVID-19 testing increased by as much as 13-fold. When an individual did test positive, isolation and contact tracing prevented further spread of COVID-19. Ultimately, the UC San Diego wastewater surveillance enabled early detection of 85 percent of COVID-19 cases on campus, according the research, published in the August 10, 2021, issue of mSystems.
What the Dashboard Can and Can’t Tell You About COVID-19 in Your Area
Many variables make state-to-state comparisons invalid — it isn’t yet known how many people have to test positive in an area for the virus to show up in the wastewater; different areas collect samples in different ways, and the sewer sheds (sampling locations) can be very different sizes. For all those reasons, wastewater surveillance is most useful when used along with case-based surveillance, which is the case-based information collected by local health authorities, according to the CDC. The dashboard uses the daily updates to compare the percentage change of concentration at the same site over the prior 15 days, how many detections there were in those 15 days, and how many samples tested positive. Sampling locations are color coded based on the rate the levels are increasing or decreasing. In the period ending February 4, the dashboard showed that 98 percent of the treatment facilities had detected the virus in all their samples. On a positive note, 75 percent of the collection sites said the amount of virus in the samples had gone down compared with two weeks before, which is a sign that the number of cases is going down.
Wastewater Data Can Help Inform What Precautions You Should Be Taking
The data from the program will be especially useful for situational awareness as testing strategies continue to change, said Kirby. Because more people are using at-home tests instead of reported clinical tests, the wastewater surveillance will be a good way to understand the level of COVID-19 in communities, she said. If the data indicates a pending surge in your area, you’ll want to be extra vigilant and follow guidelines for masking, social distancing, vaccination, and testing if you’re feeling sick, she said.
Wastewater Surveillance Could Be Used for Other Pathogens Besides COVID-19
Although the system was set up as part of the COVID-19 response, it can be applied to a wide variety of health concerns, said Kirby. Other targets include antibiotic resistance; foodborne infections such as E. coli and salmonella; norovirus influenza; and the emerging fungal pathogen Candida auris, she said. Because the infrastructure to collect and test samples is already in place, tests for new pathogens can be added fairly quickly, said Kirby. This means that if there is a new pathogen of interest, “we could ramp up the system within a few weeks to start gathering community level data on that new pathogen,” she said.
