Correlating virus in our sewage with COVID in our bodies is trickier than it seems

  • (L-R) Isabella Martin, MD, and Jacqueline Hubbard, PhD, in the laboratory at Dartmouth-Hitchcock Medical Center. Dartmouht-Hitchcock—Courtesy

Monitor columnist
Published: 1/25/2021 5:17:21 PM

Twice a week a courier picks up a bucket of pretty unsavory stuff from the Concord wastewater plant and drives it a half-hour west to the huge Dartmouth-Hitchcock Medical Center complex in Lebanon, where it joins what is basically a big wet-lab experiment.

The goal of the experiment is to help everybody use our not-so-precious bodily fluids to spot the virus SARS-CoV2. The idea is that a surge in virus numbers could give warning that a surge of cases is coming, which would let us react more quickly. It could also help pinpoint upcoming outbreaks via testing done on wastewater from certain parts of the city, or even from certain buildings.

Analyzing wastewater for social and health trends isn’t new. Notably it can be used to get a handle on drug consumption because so much of the pharmaceuticals we consume, both legal and illegal, get passed through our bodies into our feces and urine.

But doing large-scale, real-time analysis measuring DNA of one specific virus has mostly come about during the pandemic. Projects like Dartmouth-Hitchcock’s are becoming more common, including one in Keene that I wrote about last August, but figuring out the relationship between viral genetics in our sewage and COVID-19 in our bodies is more complicated that you might think.

“Here’s the tricky part. If you are following a trend and see it go up or down over time that’s easy, but this is a multi-variable situation. The concentration depends on a lot of other conditions,” said Jacqueline Hubbard, Ph.D., a clinical chemist who is co-leader of the Dartmouth-Hitchcock Medical Center’s wastewater surveillance testing project.

Hubbard listed some: “What’s the water like – is it separated from irrigation water? Was there a heavy rainfall that dilutes (the sample)? Is it a holiday weekend and everybody’s out of town?”

Then she ticked off biological variables. Only about half of people with COVID-19 shed measurable virus in their feces, for reasons that aren’t known. Maybe only sicker people shed the virus, or maybe certain age groups do, or maybe it’s purely random. And then, the sheer number of viruses per milliliter may not reflect how many people are going to get sick, which depends on whether the viral load is in the lungs or in other parts of the body.

Finally, there are process variables. Concord and other wastewater plants gather 24-hour composite samples in a “smart” bucket that collects a little bit of liquid once every hour or so for a day and mixes them all together. The alternative is a “grab sample” which collects a single, large sample at one specific time. There are plusses and minuses to using either system, and it’s not clear which could do a better job of alerting us to a SARS-CoV2 surge.

“The whole point of this study is a proof of concept that this can work as an early indicator to a rise in COVID-19,” Hubbard said.

When I heard Concord was one of nine municipalities and facilities contributing to the project, I got very excited and asked the obvious question: What do the numbers show? How much virus is being flushed down city toilets every day compared to other cities?

Hubbard gently tossed cold water on me (figuratively, that is – due to COVID, this was a phone interview).

“Right now it’s a fairly qualitative method. We have numbers but are not sure what those numbers mean,” she said.

Even the participating communities don’t see this. The lab gives general guidance about whether numbers are trending up or down, but nothing more specific.

This surprised me because the Massachusetts Water Resources Authority has a web-based chart of viruses in Boston’s wastewater that looks like charts of COVID-19 cases, although with much bigger error bars. It is based on analysis by Biobot, the Massachusetts firm that is analyzing sewage from many places, and it implies that using wastewater as an early warning indicator is accepted. Burlington, Vermont, which used to be part of the Dartmouth-Hitchcock project, has begun alerting residents based on samples from their city waste stream.

Regardless, Hubbard said that from her point of view it doesn’t seem that we know enough for raw numbers to be useful.

“We’ve been hesitant to do that with our study. … The CDC does not yet recommend it. It could be another indicator but shouldn’t be the only one,” she said. “Until we have a large enough dataset to establish a threshold … and we understand the correlation … we really can’t say. We’re still developing baselines.”

They’re also developing budgets. Hubbard says the project was funded by an “anonymous donor, whose money will run out in February. Hubbard says it would take “in the ballpark of a couple hundred thousands dollars” to keep the project going.

“Until I was involved with this I had no idea how expensive this was,” said Hubbard, who was hired by Dartmouth-Hitchcock last fall to do drug-related analysis but switched to viruses when the pandemic began.

The cost is much less than it could be because Dartmouth-Hitchcock already had much of the equipment and expertise: “If we didn’t have a lot of the automated equipment it would be half million to a million, I’d guess.”

But gathering samples, concentrating them and performing PCR tests then analyzing the data is time-consuming – 10 to 20 person-hours per week, Hubbard estimated – and time costs money.

“We need funding to help process the samples, and playing the employees,” she said. Another issue: “We’re running into supply-chain issues. … Pipette tips – it has been incredibly hard for us to get them.”

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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