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When the Covid-19 public health emergency expired in the United States on Thursday, the coronavirus will not disappear. But many of the data streams that have helped Americans monitor the virus will go dark.
The Centers for Disease Control and Prevention will stop tabulating community levels of Covid-19 and will no longer require certain case information from hospitals or testing data from laboratories. And as free testing is curtailed, official case counts, which became less reliable as Americans shifted to at-home testing, may drift even further from reality.
But experts who want to keep tabs on the virus will still have one valuable option: sewage.
People who are infected with the coronavirus shed the pathogen in their stool, whether or not they take a Covid test or seek medical care, enabling officials to track levels of the virus in communities over time and to watch for the emergence of new variants.
This approach expanded rapidly during the pandemic. The National Wastewater Surveillance System, which the CDC established in late 2020, now includes data from more than 1,400 sampling sites, distributed across 50 states, three territories and 12 tribal communities, said Amy Kirby, the programme lead. The data cover about 138 million people, more than 40 per cent of the US population, she said.
But wastewater surveillance is still missing many communities, and more work is needed to turn what began as an ad hoc emergency effort into a sustainable national system, experts said. And officials will need to be thoughtful about how they use the data as the pandemic continues to evolve.
“Wastewater has to get better,” said David O’Connor, a virus expert at the University of Wisconsin-Madison. “And we have to get a bit more savvy about interpreting what the wastewater data is telling us.”
Over the past three years, wastewater surveillance repeatedly proved its worth. When testing was widely available, the wastewater trends mirrored the official Covid-19 case counts. When testing was scarce, spikes in the viral levels in sewage provided early warnings of coming surges, allowing officials to redistribute public health resources and hospitals to prepare for an influx of cases.
Wastewater sampling helped scientists determine when new variants arrived in particular 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 surveillance system is pretty solid now,” said Marisa Eisenberg, an infectious disease public health researcher at the University of Michigan. “We’ve kind of put it through its paces.”
The CDC will still track deaths and hospitalisations, but those tend to be lagging indicators. So wastewater is likely to remain a critical early warning system for both officials and members of the public.
“It can help people who are immunocompromised, who might want to be really cautious,” said Alexandria Boehm, an environmental engineer at Stanford University and a lead investigator for WastewaterSCAN, a sewage surveillance initiative. “It can help us make decisions about whether we want to mask or go to a really crowded concert.”
As clinical testing drops off, wastewater surveillance will also be a key strategy for keeping tabs on new variants and for gauging the threat they pose, scientists said. Variants that quickly take over a sewershed or whose spread is followed by a rise in local hospitalisation rates, for instance, might warrant increased monitoring.
— The New York Times
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