Government scientists confirmed Tuesday that there has been an uptick in the presence of Covid-19 in wastewater samples across the U.S.
The potentially troubling trend comes as the country is shedding masks and easing pandemic restrictions aimed at stopping the spread of a virus that in two years has killed nearly a million people in the United States.
The federal Centers for Disease Control and Prevention acknowledged the increase after Bloomberg reported that a third of the agency’s wastewater sample sites showed a rise in Covid cases from March 1 to March 10.
That was double what it was from Feb. 1 to Feb. 10, when the highly infectious omicron variant that had roared across the country during the holiday season was starting to wane, the Bloomberg analysis of CDC data found.
“While wastewater levels are generally very low across the board, we are seeing an uptick of sites reporting an increase,” Amy Kirby, who heads the CDC’s wastewater monitoring program, said in a statement. “These bumps may simply reflect minor increase from very low levels to still low levels.”
Still, Kirby said, “Some communities though may be starting to see an increase in Covid-19 infections, as preventions strategies in many states have changed in recent weeks.”
The CDC's testing program is limited to areas that collect and report on waste water surveillance and does not provide a national representation of Covid spread, the agency said.
So it remains unclear if this is an ominous sign of things to come.
“It’s too early to know if this current trend will continue or whether we’ll see a corresponding increase in reported cases across the country,” Kirby said.
But Dr. Sadiya Khan, an epidemiologist at the Northwestern University Feinberg School of Medicine, said the recent findings are cause for “grave concern.”
“This increase is not a surprise and is of grave concern given the loosening of restrictions for activities and masking in schools and communities,” Khan said in an email. “If you look at patterns in Europe, there has been an increase in the last few days as well. If we’ve learned anything in this pandemic, it is that the trends in Europe precede our own.”
Khan was referring to a sharp rise in cases reported in Europe driven by a new variant that public health experts have been warning about even as Covid-19 cases have been steadily going down in the U.S.
Khan said we have the tools to deal with any new Covid outbreak.
“The response shouldn’t be alarm, but should focus on the things that work: masking and vaccines/boosting,” Khan said. “I am not giving up my mask anytime soon.”
Cynthia Gibas, who heads the wastewater surveillance program at the University of North Carolina at Charlotte, agreed.
"We shouldn't be in panic mode about this, but we should watch it very carefully over the next few days," Gibas told NBC News.
Sewage can show the presence of Covid-19 about a week before PCR testing can. People who have been infected shed the virus in sewage pipes several days before they show symptoms, prompting a Covid-19 test.
But wastewater isn't the only metric that could indicate a possible resurgence in Covid cases.
"Even if suddenly more people start just feeling the need to get tested, that is an indication that maybe something's happening," Gibas said.
The public health experts weighed in as the White House warned that the U.S. will soon run out of funding for future Covid booster shots, new treatments and testing efforts if spending legislation remains stuck in Congress.
At the same time, in a sign of returning normalcy, the Biden administration also announced that for the first time in two years public tours of the White House will resume on Friday and Saturdays, starting on April 15.
Currently, a little more than 75 percent of the U.S. population has received at least one vaccination against Covid-19, according to the CDC.
The unvaccinated continue to account for most of the reported Covid-19 deaths, according to analysis by the CDC and the Kaiser Family Foundation.