By Heidi Singer
Sharmistha Mishra never imagined her career as an infectious diseases physician would see her metaphorically peering into the depths of a toilet bowl. The Temerty Medicine’s researcher has found herself fascinated with the contents of sewers because of the insights they provide into the waxing and waning levels of disease in Canada.
Take measles. Or hepatitis A. Or respiratory syncytial virus (RSV). All are pathogens currently being tracked in Canada using wastewater.
For Mishra (MD’02, PGME ’06), an associate professor in the Department of Medicine who studies mpox, wastewater analysis could save lives. It could also mean countless public health dollars saved, because wastewater surveillance can be almost as accurate as costlier forms of testing.
“Across the world, people are looking at wastewater data to help us figure out how many cases of infections we might be missing with just the usual surveillance,” she says.
An unexpected beginning
Mishra’s interest in wastewater began during the COVID-19 pandemic, when a diverse range of researchers — engineers and epidemiologists, microbiologists and environmental scientists — came together in unprecedented ways to help predict surges of the virus. Brilliant in its simplicity, this surveillance technique is easier than the traditional challenge of obtaining a representative sample of blood antibodies — since everyone must eliminate.
“In my training and prior work, I never thought that researchers would be collaborating and working on modelling that would incorporate wastewater signals,” she says. “It goes to show how critical interdisciplinary science is because people were working on it long before COVID-19. But, we were just in our silos and didn’t know about it.”
In the earliest months of the pandemic, Mishra helped St. Michael’s Hospital (Unity Health Toronto) with COVID-19 modelling to plan its surge staffing. At the time, Temerty Medicine Department of Medicine Professor Sharon Straus (MD ’90, PGME ’96) and a team of engineers and front-line health workers were also testing wastewater around men’s shelters and long-term care homes, generating data that helped predict traffic into its emergency department a week or two later. The experience drove home the promise of wastewater testing for Mishra.
Next up for Mishra was wastewater testing for mpox — a practice she believes works even better than testing for COVID-19, due to the strong signals mpox gives off in feces and urine. Now, Mishra and her colleagues at the BC Centre for Disease Control and McGill University are studying whether wastewater surveillance could one day stand in for costlier blood testing —not just to discover outbreaks early but also to correct under-detection of preventable and treatable infections.
“In the modelling world, that’s what we think the promise might be,” she says.
Someone with mpox might not realize they are infected if a rash appears on the backside of their body, or if they don’t feel sick. And people may not get tested due to stigma around sexually transmitted infections. All of these problems are overridden by the flush of a toilet. Mishra recently worked on a study that found that information gleaned from wastewater data could perform about the same as blood samples in understanding the true level of mpox infection in a given place and time.
“Ideally, we’d love to have seroprevalence [blood work] data because it has more information like age, gender and social determinants of health,” she says. “Wastewater doesn’t tell you about individuals — it just provides the volume of shed virus for each catchment area. But these early studies suggest wastewater could give us almost the same information for underdiagnosis as the seroprevalence data. When we think about the resources it takes to do seroprevalence studies, wastewater gives us this alternative opportunity that is less expensive and more feasible in more places.”
Flushing cities
Meanwhile, as soccer stars hit the pitch this summer at the FIFA World Cup, Michelle Murti (MD ’06, PGME ’12), the City of Toronto’s medical officer of health, is aiming for epidemiological gold — the type that can be found in the collective contents of the city’s toilets.
With every flush, players and fans from around the world will help her team monitor the city for illness outbreaks — from measles to mpox — long before people appear in local emergency rooms. There are 300,000 guests anticipated in the city for the global event. As a result, wastewater testing will happen in the parts of the city where the fans will be.
Several years on from the pandemic, Toronto Public Health has continued to receive and report on Toronto’s sewage weekly as part of the federal program, monitoring for influenza, RSV, COVID-19, and mpox, with the testing covering about 73 per cent of the population, based on the areas where testing occurs.
During FIFA World Cup 2026, wastewater testing will be done with accelerated lab turnaround times to obtain rapid results. The testing is anticipated to take place at select areas where fans congregate. Murti says the key is to generate usable data.
“For FIFA, what can we measure that will have a very specific impact that we can action next day?” she asks. “If we detect norovirus, we know what we want to tell people and what we would activate around the site to reduce the risk of that infection.”
Murti, an adjunct professor at U of T’s Dalla Lana School of Public Health (DLSPH), is especially interested in monitoring for measles during the games, given the large international audience expected.
It’s much less invasive than going into a building and swabbing everybody
“We’ll sample the day before, day of and day after for each game at the Toronto Stadium, and get results a few days later,” she says. The highly infectious virus remains “in the air even two hours after someone with measles has left. We can now say people will have been exposed, and we can put that alert out to our clinician partners.”
The art of preparation
Preparing for potential outbreaks means laying the groundwork for collaboration in advance, should an issue occur. The practice has strong roots in the COVID-19 pandemic era, when scientists and clinicians reached out and shared information across institutions and regions to understand the possibilities of wastewater testing. It could also come in handy if a positive test signalling a disease outbreak occurs, so hospitals, clinics and other health care providers can be alerted.
During the COVID-19 pandemic, for example, Temerty Medicine researchers such as Straus connected with peers in Ottawa, Regina and B.C. as well as environmental scientists at Toronto Metropolitan University, who used DIY methods, including lowering tampons on fishing wire down sewer grates, to obtain samples from Toronto’s Victorian-era sewers.
Straus first saw the need for highly local surveillance during the initial wave of COVID, when an entire busload of patients from a nearby housing shelter arrived at the hospital. Testing around shelters and long-term care homes allowed clinicians and researchers, including Toronto Public Health and Inner City Health Associates, to collaborate to contain local outbreaks. Soon, a robust wastewater testing program was adopted by the Ontario COVID-19 Science Advisory Table, which is based at DLSPH. Straus never saw another busload of patients.
Unintended consequences?
The prospect of such highly localized testing raises concerns about data privacy, especially since some jurisdictions around the world monitor wastewater for illicit drugs and share results with law enforcement. Surveilling buildings could stigmatize a community and lead to harm if the data falls into the hands of industries such as insurance or real estate, says U of T bioethicist Alison Thompson (PhD ’05).
“It’s much less invasive than going into a building and swabbing everybody,” says Thompson, an associate professor in the Leslie Dan Faculty of Pharmacy. “So, from my perspective, it’s the least invasive way to survey a population. But all the usual public health protocols should still apply because once you start looking, there’s no shortage of ethical issues to think about.”
Wastewater testing “sounds low risk from an ethical standpoint, but I don’t think it is,” adds Thompson.
“This has potential to undermine trust by stigmatizing groups of people or sensationalizing the data. When people are looking for a home to buy in a certain neighbourhood, will they want to see the use of drugs or even [the prevalence of] infectious diseases? I think this data is actually quite sensitive and should be viewed that way,” she says.
So far, Canadian data is secure in the public health sphere, but Thompson has already seen U.S. companies advertising wastewater testing to employers interested in finding drug violations among workers. As the technology continues to improve, she wonders how private industry will enter the picture. Mishra, too, strikes a note of caution about the possibilities of wastewater surveillance, as with any emerging technology.
“We have to be careful with the whole magic bullet thing because one data stream is not going to be enough,” she says. “Just like one medication is not the silver bullet in treating patients.”