If the public health emergency in the United States ends on Thursday, the coronavirus will not go away. But many of the data streams that have helped Americans keep tabs on the virus will go dark.
The Centers for Disease Control and Prevention will stop tabulating levels of Covid-19 in the community and will no longer require certain case information from hospitals or test data from labs. And as free testing is being curtailed, the number of official cases, which became less reliable as Americans transitioned to home testing, may be even further off the mark.
But experts looking to keep an eye on the virus still have one valuable option: sewerage.
People infected with the coronavirus shed the pathogen in their stools whether or not they undergo a Covid test or seek medical care, allowing officials to monitor levels of the virus in communities over time and can watch the emergence of new variants.
This approach expanded rapidly during the pandemic. The National Wastewater Monitoring System, which the CDC established in late 2020, now includes data from more than 1,400 sampling sites across 50 states, three territories and 12 tribal communities, said Amy Kirby, the program leader. The data covers about 138 million people, more than 40 percent of the US population, she said.
And as other tracking efforts wind down, some communities are rushing to establish wastewater monitoring programs for the first time, Dr. Kirby up. “This actually leads to more interest in wastewater,” she said.
In the coming months, wastewater monitoring will become even more important, scientists said, and it should help officials detect incipient outbreaks.
But wastewater monitoring still misses many communities, and more work is needed to turn what started as an ad-hoc emergency effort into a sustainable national system, experts said. And officials will have to think carefully about how they use the data as the pandemic continues to unfold.
“Wastewater needs to get better,” said David O’Connor, a virologist at the University of Wisconsin-Madison. “And we need to get a little smarter about interpreting what the wastewater data is telling us.”
Wastewater monitoring has proven its worth time and time again over the past three years. When testing was widely available, wastewater trends reflected the official number of Covid-19 cases. When testing was scarce, spikes in viral levels in sewage provided early warnings of upcoming spikes, allowing officials to reallocate public health resources and hospitals to prepare for an influx of cases.
Wastewater sampling helped scientists determine when new variants arrived in certain communities and helped clinicians make more informed decisions about when to use certain treatments, which may not work against all versions of the virus.
“For SARS-CoV-2, our wastewater monitoring system is now pretty solid,” Marisa Eisenberg, an infectious disease epidemiologist at the University of Michigan, said. “We put it to the test a little bit.”
Houston, for example, now has an extensive monitoring of waste water infrastructure, taking weekly samples from all of the city’s 39 wastewater treatment plants, as well as individual schools, shelters, nursing homes and prisons. The city has no plans to scale back, said Loren Hopkins, chief of environmental science for the Houston health department and a statistician at Rice University.
“We really don’t know what Covid is going to do,” she said. “We continue to look at the wastewater to tell us how much of the virus is there.”
The CDC will still track deaths and hospitalizations, but those are mostly lagging indicators. Thus, wastewater is likely to remain a critical early warning system for officials and members of the public alike.
“It can help people who are immunocompromised, who may want to be very careful,” said Alexandria Boehm, an environmental engineer at Stanford University and a principal investigator for WastewaterSCAN, a sewer monitoring initiative. “It can help us decide if we want to mask up or go to a really busy concert.”
As clinical testing wanes, wastewater surveillance will also be an important strategy for keeping tabs on new variants and measuring the threat they pose, scientists say. For example, variants that quickly take over a sewage system, or whose spread is associated with an increase in local hospital admissions, may warrant increased monitoring.
Open to interpretation
However, the data will not be available everywhere. Because the existing wastewater monitoring system came about in a somewhat haphazard manner, with interested jurisdictions opting for it, coverage of the country is uneven. Wastewater sampling sites are usually sparse or absent in many rural areas and parts of the South and West.
And collecting wastewater data is just the first step. Understanding it could be trickier, scientists warned.
Among the challenges they cited: Now that many Americans have developed some immunity to the virus, sewage spikes aren’t necessarily leading to the same wave of hospitalizations that some institutions are used to. And scientists still do not know whether all variants are equally detectable in wastewater.
Moreover, simply spotting a new variant in the wastewater does not necessarily mean a problem. For example, Marc Johnson, a virologist at the University of Missouri, and his colleagues have found dozens of unusual variants in wastewater samples in the United States since 2021.
Some of these variants are radically different from Omicron and, in theory, could pose a new risk to public health. But so far, these variants don’t seem to be spreading. They likely come from individual, dying patients with long-term coronavirus infections, said Dr. Johnson.
“Wastewater is really good because it can give you a comprehensive picture of what’s going on,” said Dr. Johnson. But there are times, he said, “where it can mislead you.”
And while a reduction in Covid case tracking was probably inevitable, wastewater surveillance is most informative when combined with other sources of public health data, scientists say. “I prefer to think of it as an additional data stream,” said Dr. Eisenberg.
Optimize the system
Wastewater monitoring will continue to evolve, said Dr. Kirby. The CDC is talking to some states about how to optimize their sampling site network, a process that can involve both adding new sites and scaling back in areas where multiple sampling sites provide essentially redundant data.
“We expect a reduction in the number of sites in some of those states,” said Dr. Kirby. “But we will work with them to be strategic about that so we don’t lose any information.”
are officials explore other options, at. As part of the CDCs Traveler Genomic Surveillance Programfor example, Ginkgo Bioworks, a Boston-based biotechnology company now testing waste water samples of planes landing at the international terminal of San Francisco International Airport.
“It’s really important to put in place these indirect mechanisms that can give you a sense of what’s happening in the world as other forms of testing begin to decline,” said Andrew Franklin, the director of business development at Concentric by Ginkgo , the director of the company. biosafety and public health department.
The US bailout has raised enough funds to monitor wastewater in all states and territories through 2025, Dr. Kirby said.
But maintaining wastewater monitoring requires ongoing, longer-term funding, as well as ongoing support from local officials, some of whom may lose interest as the emergency phase of the pandemic winds down. “We’re going to see some fatigue-based dropouts,” said Guy Palmer, an infectious disease pathologist at Washington State University and the chair of the wastewater surveillance committee of the National Academies of Sciences, Engineering and Medicine.
So proponents of wastewater monitoring hope to demonstrate its continued usefulness, both for Covid-19 and other diseases. Some jurisdictions already use wastewater to detect flu and other pathogens, and the CDC hopes to roll out comprehensive testing protocols by the end of the year, said Dr. Kirby.
“This is part of our long-term surveillance portfolio,” said Dr. Kirby. “I think we’re really going to see how powerful it can be once we get out of this emergency period.”