Since people shed the coronavirus in their feces before showing symptoms or testing positive, wastwater surveillance of virus levels is intended to serve as an early warning system for upcoming surges or new variant detection. But these efforts are patchy in the U.S.
The CDC's SARS-CoV-2 surveillance map shows many of the 732 sampling sites that report data to the agency are concentrated in the Midwest and Northeast. Overall, just a dozen states — California, Colorado, Illinois, Missouri, North Carolina, New York, Ohio, Rhode Island, Texas, Utah, Virginia and Wisconsin — routinely submit data to the CDC's National Wastewater Surveillance System, which the agency launched in September 2020, Politico reports.
Even in states regularly submitting wastewater samples, information isn't uniform. For example, of the 23 collection sites in California, most of them are clustered in the Bay Area. Further, not all communities have the resources to leverage this tool. Wastewater testing initially took off in urban areas and university towns where there was access to research expertise and equipment, The Los Angeles Times reports.
"You should be injecting more resources in places that are underserved since they have the disproportionate burden of disease," Colleen Naughton, PhD, an engineering professor at the University of California Merced who is helping set up wastewater testing in several smaller towns in the state, told the LA Times.
Experts have also expressed concern that information on the CDC's wastewater surveillance dashboard can be misinterpreted. For instance, the dashboard presents percent changes in virus detection. For the 15-day period ending March 17, coronavirus levels rose at 40 percent of sampling sites, but some of the changes may not reflect big shifts in risk level.
"The CDC is presenting relative viral concentration (percent change). But, that may be deceptive. You can have a 1000 percent increase that takes you from 'very low risk' to 'low risk,' the Pandemic Prevention Institute said in a series of March 16 tweets.
Looking at CDC's map alone, it's hard to spot trends, as there are some counties where some sampling sites show an increase in virus levels, and others show a decrease.
"Wastwater is a powerful tool to detect COVID-19 surges, but only if data are analyzed and presented so that policymakers and communities know how to respond," the Pandemic Prevention Institute tweeted. "Are we in the earliest days of another surge? We might be. But using the CDC wastewater metrics, we just don't know."