COVID tracker: Testing sewage is one way to see how bad the pandemic is

  • Biomarkers of COVID have soared in Boston's sewage Mass Water Authority—Courtesy

Monitor staff
Published: 1/9/2022 1:00:58 PM

The pandemic has taught us many things, one of which is that it’s hard to keep track of a disease.

Short of conducting daily COVID-19 tests on a random chunk of the population, we can only make estimates about how the pandemic is progressing based on bed counts, test reports and death certificates, all of which have issues. That’s part of the reason we can’t get our act together to combat it.

Wouldn’t it be nice to have a technology that provides one number that tells exactly how good or bad things are? To lay folk like me, sewage monitoring sounds like that technology.

Under this system, samples of wastewater are sent to labs that perform their PCR magic to find DNA and other biomarkers in our stool and urine that indicate the presence of COVID-19 viruses.

The Massachusetts Water Resources Authority does such monitoring at the huge Deer Island treatment plant and posts the results online. No need to wait for people to get sick or go to the hospital to know what’s happening in Boston: 100,000 flushes give the information.

That’s the goal, anyway. The reality isn’t quite that straightforward.

“It can’t tell the exact number, but it does give a trend,” said Tricia Tilley, director of the Division of Public Health Services for the state.

As I’ve reported a few times, some colleges in New Hampshire including Keene State and UNH are using this system to help spot potential outbreaks in dorms. New Hampshire Public Health Services regularly tests the wastewater from its huge New Hampshire Hospital campus for the same reason.

“Especially for asymptomatic transmission, it’s very valuable. It’s the proverbial canary in the coal mine,” Tilley said. “It’s another tool in the toolbelt.”

This system can never provide the complete picture for New Hampshire because more than half of our households are on septic systems rather than city sewer. More importantly, though, researchers are still pinning down the correlation between biomarkers in sewage and disease outbreaks.

You can’t just say more of one equals more of the other because there are so many variables. Different variants cause different levels of disease at different rates, but also weird stuff can produce misleading results – ranging from heavy rainfall, which can dilute wastewater, to holidays, which abruptly change the sample population by bringing visitors here and sending locals away.

Many places are trying to sort through these complexities, including Dartmouth-Hitchcock Medical Center in Lebanon. Some cities send regular samples to DHMC’s labs as they work to correlate samples with reality. (Concord no longer does this; it may participate in a similar CDC program soon.) The state is also interested.

“We’re in those conversations right now: How do you use this information to help inform our epidemiology?” said Tilley. “The next step is to understand what the municipalities are receiving for information and what that means for an even broader population.”

New Hampshire is also working to improve the collection and analysis of data. “We’re to do some work with the UNH laboratory in particular, to see if they need additional equipment and understand what data we should get to inform the state’s bigger picture,” she said.

Realistically, though, we’re never going to have a single number that explains how things are going with this pandemic – or the next one, because there will be a next one.

“It will never replace the reporting of individual test cases. It’s not a magic bullet, but it’s certainly interesting data, useful data, that helps us understand trends,” Tilley said.

What’s the trend on the spread and impact of the disease? Bad, and the worst seems yet to come.

The number of COVID-19 cases in the hospital has been fairly steady for the past two weeks but, as NHPR reported, that doesn’t count the number of “COVID-recovering patients” filling beds, often because shortage in long-term care facilities means they have nowhere else to go.

If you include those patients, the impact of COVID-19 on state hospitals has not improved in more than a month.

Meanwhile, the total tally of deaths has topped 2,000 and is growing at the fastest pace since the very peak of last winter’s surge.

David Brooks bio photo

David Brooks is a reporter and the writer of the sci/tech column Granite Geek and blog, as well as moderator of Science Cafe Concord events. After obtaining a bachelor’s degree in mathematics he became a newspaperman, working in Virginia and Tennessee before spending 28 years at the Nashua Telegraph . He joined the Monitor in 2015.

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