Sewage can give a week’s extra warning of coronavirus spikes: study
On April 16, the novel coronavirus peaked in New Haven, Conn., at least as far as tests of individuals showed.
But Yale University scientists taking samples from the local sewage treatment plant got a head start on that information: they could see the peak almost immediately, on April 7.
Someone with the coronavirus can take up to five days to show symptoms. To show up in statistics, they then have to seek out testing, be tested and have the results come back.
But long before all that has time to happen, the person has been contributing data to the sewers with every flush.
For University of Ottawa engineering professor Robert Delatolla, sewage offers us a way to find out about future outbreaks as quickly as possible.
He calls the New Haven study “potentially very important.”
New Haven’s sewage (red) showed a spike in coronavirus about a week before it was shown in tests of people (black).
“It indicates that it could be a tool for us, or our health agencies to use, for early detection, or to catch the next wave,” he says.
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“When the multiple waves come, we don’t want to miss a couple of days. We want to catch it.
“If there’s a signal in that wastewater, we want to catch it.”
The Yale researchers were thinking along similar lines.
“Decisions to implement or relax public health measures and restrictions require timely information on outbreak dynamics in a community,” they wrote.
“There is a pressing need for additional methods for early sentinel surveillance and real-time estimations of community disease burden so that public health authorities may … plan epidemic responses accordingly.”
One hard lesson of the pandemic is that societies that have been slow to react have paid bitterly for it.
British epidemiologist Anthony Costello blamed that country’s death rate, now the world’s highest, on a slow response to the outbreak by government.
“We have to face the reality,” he said in late April. “We were too slow with a number of things. We could see 40,000 deaths by the time it’s over.” (The U.K.’s official death toll is now over 37,000.)
University of Ottawa researchers have been taking sewage samples from Ottawa and Gatineau treatment plants since early April, with the goal of doing something similar to the Yale study, Delatolla says.
One advantage of seeing sewage as a database is that everyone in the community, rich or poor, sick or well, symptomatic or asymptomatic, ends up contributing to it.
“This seems to be a means to capture a picture of what’s going on in the community, the entire community, at one time, which is great.”
Delatolla’s challenges include deciding how best to measure the coronavirus in sewage — what point in the flow through the treatment plant the sample is taken from turns out to matter — and how to deal with heavy rain making its way into the sewers.
“When we have massive rain events in Ottawa, that gets diluted,” he says. “When we have the snow melt, when it all melts and goes into our sewers, we know that that gets diluted by half, by four times.”
The solution, he says, involves using other chemicals that are shed into the sewers at a constant rate, like ibuprofen, and using that as a reference point.
As a sewage monitoring system became more sophisticated, it could be used at a more local level, he says: schools, neighbourhoods, long-term care homes.
Still, human waste is one of the things in our lives that we want as little to do with as possible. While his research has a serious purpose, Delatolla acknowledges its odd side, as scientists across North America urgently send each other samples of sewage.
“It’s funny. People are exchanging it. We’re shipping this to each other all over now, like it’s a valuable commodity.”
Once the Ottawa scientists decide on a way of measuring coronavirus samples in sewage, there are lots of samples to work with.
Since 2018, Statistics Canada has been collecting monthly sewage samples from Vancouver, Edmonton, Toronto, Montreal and Halifax (originally to test for illegal drugs) and those samples are all there to be analyzed.
For example, when did the coronavirus start showing up in Edmonton’s sewers? The samples are ready to help answer the question.
“Honestly, we have a great history now,” Delatolla says. “We have all these great samples.”
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