Across Canada, scientists are working out how to build an early warning system for a second wave of the novel coronavirus based on a substance we don’t want to look at, think about, or be near: human waste.
And they hope to refine their sewage-based surveillance system to the point that it can monitor individual neighbourhoods or institutions, like long-term care homes, they say.
The system they’re developing now is focused on the coronavirus, but they say they’re hoping it will have a longer-term use dealing with future diseases.
“Everybody has to poop,” says Ryerson University professor Kimberly Gilbride. “It’s something that we can’t avoid.”
Testing statistics for the coronavirus don’t tell the whole story: not everyone with the disease gets tested or shows symptoms in the first place. But there can be no secrets in the sewer, since everybody contributes.
“People can’t opt out of it, so it’s going to give us a really good idea of what’s happening in the communities,” she says.
Gilbride and fellow Ryerson professor Claire Oswald are involved in a project to set up a sewage monitoring system in Toronto. They explain that they’re still in an experimental stage, but that they expect to start measuring virus levels in earnest by the end of the month.
One of the most advanced systems is in Ottawa, where scientists have moved beyond an experimental stage and are testing that city’s sewage for the coronavirus every other day, updating local public health officials with the results.
Levels found in Ottawa’s sewage closely track known levels of the virus in the community, University of Ottawa engineering professor Robert Delatolla wrote in an e-mail.
One thing sewage monitoring could give us is early warning of a second wave, Oswald says.
“If the virus … levels in wastewater that we’re tracking are sort of steady, and then all of a sudden they start to move up again, that may be an indication that a second wave is coming.”
Testing can be slow, but newly infected people shed the virus into the sewage system more or less immediately. In New Haven, Conn., virus levels in sewage closely tracked those shown in tests, but a full week earlier.
Oswald says they hope to move beyond testing at treatment plants, which can handle the waste of hundreds of thousands of people, to smaller-scale monitoring at more local levels that would give public health officials a precise idea of where new outbreaks are starting.
“Because we are going to attempt to look at finer geographic areas in our sampling, we are going to be able to compare those areas to see if a particular location or neighbourhood has a potentially higher infection rate than other neighbourhoods, and people in those areas would be at a greater risk,” she says.
Ideally, a system should be able to look for “hot spots of potential infection, like the long-term care facilities, hospitals or even jails.”
One complication in Toronto is that parts of the city still have combined storm sewers, where human waste and rainfall share the same system. Heavy rain, or snowmelt, has the potential to throw measurements off.
“We’ll be avoiding sampling during rain events, or shortly after heavy rainfall events, when there is the potential for sanitary and storm to be mixing, which would dilute the sample,” Oswald says.
The work now being done is a foundation for tracking some other disease that may appear in the future, Oswald says. Israel got an early warning of a 2013 polio outbreak because officials there were monitoring sewage, for example.
“One really long-term vision is that if this whole sewer surveillance tool works out really nicely, really, it puts us in a great spot if the city is ever inundated by any other infectious agent that happens to be in human feces, we should be able to very, very rapidly develop a test so that we can detect it,” she says.
“For now it’s for COVID-19 infections, but in the future, it could be for anything that public health might be interested in tracking through the sewer system.”
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