A passenger wears a face covering on a train in Washington, D.C. last week as coronavirus cases increase across the United States.

A passenger wears a face covering on a train in Washington, D.C. last week as coronavirus cases increase across the United States. (Matt McClain/The Washington Post)

There’s no question a winter coronavirus wave is washing over the United States. How big of a surge is a far murkier question.

The dramatic scale-back of coronavirus surveillance data has made it harder to grasp the magnitude of covid-19 surges.

Some experts and advocates of heightened coronavirus precautions are citing wastewater tracking to declare that we’re in the second-highest surge of the pandemic. It’s a disputable claim, but not baseless, for reasons we’ll outline below.

The Centers for Disease Control and Prevention uses more restrained language, describing high levels of covid-19 activity, with the infected far less likely to become seriously ill.

As with all things related to coronavirus data, there are asterisks and important caveats to every metric. And it gets especially tricky comparing surges. Here’s some guidance from experts on the best way to interpret data:

What wastewater data tells us

Health officials look beyond doctors’ offices and testing sites and into sewers to understand how the coronavirus is circulating in communities. This can capture the asymptomatic and mild cases that usually stay off the public health radar.


Taken at face value, wastewater tracking does seem to suggest we’re seeing the highest levels of the virus since the massive wave of omicron cases in winter 2021-2022 (the first surge with widespread wastewater surveillance), though nowhere near the height of omicron.

The CDC’s examination of surveillance sites nationwide shows coronavirus levels in wastewater now exceeding last winter’s peak, though the agency official monitoring the data described the levels as comparable. Other institutions tracking wastewater, including Biobot Analytics and WastewaterSCAN, also show levels slightly higher than they were a year ago.

But experts caution against declaring that we’re in the second-highest surge based on sewer surveillance.

“It’s obviously detecting the amount of copies of the virus, but that doesn’t necessarily mean it’s a direct match to the number of cases,” said John Brownstein, who directs the Computational Epidemiology Lab at Boston Children’s Hospital and has studied how to use surveys to estimate the prevalence of coronavirus in communities. “We just need to be careful about extrapolating these results to numbers that could create fear and anxiety.”

Changes in wastewater data are also influenced by how many treatment plants are participating in surveillance and the methods used to monitor samples. Other factors that could influence how much virus people are shedding, include their levels of immunity and the variant infecting them, though wastewater trackers say it’s unclear whether those factors explain the increase in coronavirus in the wastewater over the past year.

“The numbers are bigger, but is it meaningfully larger?” said Amy Kirby, who oversees wastewater surveillance at the CDC. “That will tell us there are more infections in those communities, but I don’t know if it’s going to have any impact. Our hospitals aren’t necessarily feeling greater stress than they did last year.”

What hospital data tells us

Kirby’s comment illustrates how the CDC and other health officials are fixated on the strain on hospitals as a measure of the pandemic’s severity.


Hospitals no longer have to report suspected covid-19 cases after the public health emergency ended in May. But they are still required to report laboratory-confirmed covid-19 cases through the end of April, and that is the metric the CDC has used to track hospitalizations over time.

By that measure, nearly 35,000 Americans were newly hospitalized with covid-19 in the week of Dec. 30. Weekly hospitalizations peaked last winter at 44,000 around this time last year.

Hospitals no longer test everyone for the coronavirus, which could explain some of the decrease. But people admitted with respiratory illnesses are typically tested. CDC officials, the American Hospital Association and other experts say this change in practice makes the data more accurate.

“When the hospital reports someone having covid, then it’s likely covid is the reason for the admission because there’s no longer this large-scale screening of every patient,” said Theo Vos, a professor emeritus at the Institute for Health Metrics and Evaluation at the University of Washington.

Wastewater data also provides a useful planning signal for hospitals if they need to prepare to fortify staffing or add more beds during what is already a busy time of year.

Kirby said there are signs the coronavirus may be peaking in wastewater, but the next few weeks will tell whether hospitals need to worry about a protracted season.

“What this is more likely telling us is there are a lot of mild cases of covid - even asymptomatic cases of covid - in the community, and it’s just not causing as much severe infection, likely because of high rates of vaccination,” Kirby said of wastewater trends.

What this all means

For the lay person, does it really matter whether the national coronavirus surge is higher this year? Some experts don’t think so.

Your odds of contracting the virus are greater this time of year, just like they were every pandemic winter. If you have a lower risk tolerance or if you or people you spend time with are at risk for severe illness, it’s a good time for precautions.

Instead of looking at wastewater to understand how rampant the coronavirus is, experts advise using it to understand which way the virus is trending.

“You could view it as a weather report. Some people will look at the weather and say, ‘Oh it’s raining today and I’ll work from home.’ Other people don’t care and will go running in the rain,” said Alexandria Boehm, an engineering professor at Stanford University and program director of WastewaterSCAN. “You get the information. You choose how to use it.”

Throughout the pandemic, the primary goal of virus restrictions has been not to stamp out transmission, but to protect the health-care system from becoming overwhelmed. The measures to “flatten the curve” in the early pandemic months by shutting businesses and keeping people at home were meant to prevent a surge of patients who were critically ill with an unfamiliar pathogen from overwhelming hospitals.

Now, doctors know how to treat covid-19 and patients are discharged more quickly. “Not all hospitalizations are equal,” said Jeffrey Shaman, an epidemiologist at Columbia University.


Weekly covid fatalities, averaging 1,500 between Thanksgiving and Christmas, have risen slightly since hospitalizations started rising in early November. Those deaths are less than half the fatalities a year ago. It’s possible the December death toll will rise as new data is examined, but Shaman said the evidence so far suggests patients hospitalized with covid are less likely to die compared with last winter.

Without hospitals warning that they are on the brink of collapse, government officials are highly unlikely to bring back measures such as mask requirements or vaccine mandates to enter public establishments. Some critics of this public health approach say it neglects other consequences of widespread transmission, including long covid.

“That’s not something that’s going to necessarily show up in 30-day hospitalization statistics,” said Michael Hoerger, an assistant professor of psychology at Tulane University whose unofficial wastewater forecasts have reached large audiences on social media. “I would really like to see the CDC talk clearly about these issues and recommend masking, remote activities and vaccination, and tie what we are seeing in transmission to actionable behaviors.”

Covid-19 has consequences beyond hospitalizations. It can leave people feeling awful, disrupt plans and force people to stay home or miss school.

For most Americans, it is unlikely you’ll become seriously ill or develop lasting complications, especially if you are vaccinated. But when you look at the virus’s toll on society, the pandemic has taught us over and over again that a small percentage of a huge number is still a big number.

Even if the chances of developing long covid for otherwise healthy people are low and have been getting lower since the pandemic started, it can still add up to thousands of Americans if millions are getting sick in a surge.

And even though death rates for the vaccinated are low, the most vulnerable have a harder time dodging the virus in a surge and thousands will die.

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