Move over, case rates and hospitalizations. The next generation of COVID tracking is here.

By Betsy Ladyzhets

It is a truth universally acknowledged among health experts that official COVID-19 data are a mess right now. Since the Omicron surge last winter, case counts from public-health agencies have become less reliable. PCR tests have become harder to access and at-home tests are typically not counted.

Official case numbers now represent “the tip of the iceberg” of actual infections, Denis Nash, an epidemiologist at the City University of New York, told me. Although case rates may seem low now, true infections may be up to 20 times higher. And even those case numbers are no longer available on a daily basis in many places, as the CDC and most state agencies have switched to updating their data once a week instead of every day.

How, then, is anyone supposed to actually keep track of the COVID-19 risk in their area—especially when cases are expected to increase this fall and winter? Using newer data sources, such as wastewater surveillance and population surveys, experts have already noticed potential signals of a fall surge: Official case counts are trending down across the U.S., but Northeast cities such as Boston are seeing more coronavirus in their wastewater, and the CDC reports that this region is a hot spot for further-mutated versions of the Omicron variant. Even if you’re not an expert, you can still get a clearer picture of how COVID-19 is hitting your community in the weeks ahead. You’ll simply need to understand how to interpret these alternate data sources.

The problem with case data goes right to the source. Investment in COVID-19 tracking at the state and local levels has been in free fall, says Sam Scarpino, a surveillance expert at the Rockefeller Foundation’s Pandemic Prevention Initiative. “More recently, we’ve started to see lots of states sunsetting their reporting,” Scarpino told me. Since the Pandemic Prevention Initiative and the Pandemic Tracking Collective started publishing a state-by-state scorecard of breakthrough-case reporting in December 2021, the number of states with a failing grade has doubled. Scarpino considers this trend a “harbinger of what’s coming” as departments continue to shift resources away from COVID-19 reporting.

Hospitalization data don’t suffer from the same reporting problems, because the federal government collects information directly from thousands of facilities across the country. But “hospitalizations often lag behind cases by a matter of weeks,” says Caroline Hugh, an epidemiologist and volunteer with the People’s CDC, an organization providing COVID-19 data and guidance while advocating for improved safety measures. Hospitalizations also don’t necessarily reflect transmission rates, which still matter if you want to stay safe. Some studies suggest, for example, that long COVID might now be more likely than hospitalization after an infection.

For a better sense of how much the coronavirus is circulating, many experts are turning to wastewater surveillance. Samples from our sewage can provide an advanced warning of increased COVID-19 spread because everyone in a public-sewer system contributes data; the biases that hinder PCR test results don’t apply. As a result, Hugh and her colleagues at the People’s CDC consider wastewater trends to be more “consistent” than constantly fluctuating case numbers.

When Omicron first began to wreak havoc in December 2021, “the wastewater data started to rise very steeply, almost two weeks before we saw the same rise” in case counts, Newsha Ghaeli, the president and a co-founder of the wastewater-surveillance company Biobot Analytics, told me. Biobot is now working with hundreds of sewage-sampling sites in all 50 states, Ghaeli said. The company’s national and regional dashboard incorporates data from every location in its network, but for more local data, you might need to go to a separate dashboard run by the CDC or by your state health department. Some states have wastewater surveillance in every county, while others have just a handful of sites. If your location is not represented, Ghaeli said, “the wastewater data from communities nearby is still very applicable.” And even if your county does have tracking, checking up on neighboring communities might be good practice. “A surge in a state next door … could very quickly turn into a surge locally,” Ghaeli explained.

Ghaeli recommends watching how coronavirus levels in wastewater shift over time, rather than homing in on individual data points. Look at both “directionality” and “magnitude”: Are viral levels increasing or decreasing, and how do these levels compare with earlier points in the pandemic? A 10 percent uptick when levels are low is less concerning than a 10 percent uptick when the virus is already spreading widely.

Researchers are still working to understand how wastewater data correlate with actual infections, because every community has unique waste patterns. For example, big cities differ from rural areas, and in some places, environmental factors such as rainfall or nearby agriculture may interfere with coronavirus tracking. Still, long-term-trend data are generally thought to be a good tool that can help sound the alarm on new surges.

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