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As covid testing increasingly moves home, knowledge of wastewater is no longer in sync with case and hospitalization rates, according to a new study.
By Émilie Anthès
Early last year, while the U. S. As the U. S. government grappled with a record surge of covid-19, the degrees of coronavirus in a community’s water were closely aligned with two other statistics that measured the virus’ toll: local case rates and hospitalizations. But until last fall, the measurements were out of sync and tewater data was no longer such a smart indicator of the number of officially reported cases or hospitalizations, according to a new study published Wednesday in JAMA Network Open.
Still, the location highlights why knowledge of wastewater is so useful, the researchers say. One explanation for why the numbers no longer line up, the study authors suspect, is that the number of cases is unreliable, especially as more Americans have begun taking credit for Covid at-home testing, while sewage remains a reliable measure.
In addition, as the pandemic continued, more people developed immunity to the coronavirus and treatments improved, likely leading to fewer hospitalizations even when infection rates were high.
Even if other people inflamed with the coronavirus never seek testing or treatment, they excrete the virus in their feces. This has made wastewater tracking a useful way to track the amount of virus circulating in a community. At the height of the pandemic, sewage knowledge provided early warning of upcoming waves of strength and helped experts monitor the spread of new variants.
Now that the emergency phase of the pandemic is over, wastewater tracking is an even bigger tool, experts say. This spring, the Centers for Disease Control and Prevention stopped calculating covid levels online and collecting other types of tracking data.
Although hospitalization rates have declined, the virus still poses dangers, especially for others with weakened immune systems. Local knowledge of wastewater can help other people and institutions, such as long-term care facilities, make more informed decisions about when to take more precautions, the researchers said.
In September 2020, the C. D. C. established a national wastewater tracking formula to centralize and standardize efforts to track coronavirus in wastewater. Since then, the formula has been expanded to cover more than 1,000 sampling sites across the country.
For the new study, researchers publicly analyzed available wastewater data from 268 counties participating in the national tracking system. They compared wastewater trends in each county with local case and hospitalization rates in the first three quarters of 2022.
From January to March, an era that overlapped with Omicron’s winter surge, higher levels of the virus in wastewater largely reflected higher rates of cases and hospitalizations, the scientists found. Wastewater levels were lowest in the April-June era, before returning to the July-September era. But over the past three months, when sewage levels were high, official case and hospitalization rates remained relatively low.
“Although we saw an increase in case rates, it wasn’t as large as what we saw in the wastewater data,” said Dr. Brown. Meri Varkila, a postdoctoral fellow at Stanford University and an author of the new study. even alidea’s wastewater is probably the most accurate estimate of what’s happening in terms of Covid occurrence in communities across the country. “
The coronavirus is constantly evolving. We assume that inherently, the virus has not drastically replaced how it spreads and how it behaves in the environment,” said Dr. Shuchi Anand, a Stanford nephrologist and the study. But possibly there would be long-term variants appearing in wastewater more or less smoothly than variants beyond.
The sensitivity of the population will also change, as other people revel in more infections, new vaccines are rolled out, and immunity waxes and wanes. These changes can make it difficult to wait for what long-term spikes in wastewater levels mean for public health.
Wastewater awareness will remain maximum when tested alongside other public fitness parameters, the researchers said.
Emily Anthes is a reporter at The Times, where she focuses on science and fitness and covers topics such as the coronavirus pandemic, vaccines, viruses and covid in children. Learn more about Émilie Anthès
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