Why contact tracing will be key to our path out of lockdown
Health units overwhelmed when second wave hit have yet to resume full tracking of cases
A young man attends a small dinner with six people, where he is exposed to someone silently harbouring the virus . Feeling fine, he heads to a child’s birthday party a few days later, infecting several others. One of the people at the birthday then unknowingly passes the disease on to their mother. The mother dies.
In public health units across the province, contact tracers have raced to call everyone who has been in close contact with a positive case so they can be isolated and tested, in an effort to stop cycles of COVID-19 transmission like this.
But in the fall, as cases surged, overwhelmed health units in
Toronto, Peel and Simcoe-Muskoka had to triage, contact tracing only the highest-risk cases. Months later, despite dozens of new hires, it’s still not completely back.
Now a drop in provincial case numbers is sparking talk of possibly lifting some lockdown restrictions. But that can’t be done without a strong contact tracing system in place, experts say, especially with more contagious variants in the mix. And vaccines won’t magically solve everything, at least not right away.
“We stopped contact tracing effectively in Toronto around Thanksgiving, and it’s now four months later and nothing is happening,” said Dr. Zain Chagla, an infectious diseases physician at St. Joseph’s hospital in Hamilton and an associate professor at McMaster University.
Mass vaccination has gone from a hope to a reality on the horizon, but “we’re currently in very strict lockdown, and we don’t want to stay in lockdown until everybody is vaccinated,” said Ashleigh Tuite, epidemiologist and assistant professor at the University of Toronto.
“The whole point of lockdown is to give us some time to bring case numbers down and also give us the opportunity to get back on track with testing and tracing.”
Testing is in a better place, with increased capacity, she said. But if you can’t keep up with contact tracing now, “it gets exponentially harder once you’re in a situation where you have people moving around more, which is what happens when you ease up on these restrictions.”
This is “even more important” with new, more contagious variants of the disease. Backward contact tracing — to find the source of an infection and other people who may have been infected, and quickly quarantine them — would be helpful in these cases, Tuite added.
The province is “working very closely” with public health units to ensure that individuals with the new variants of concern are “prioritized for case and contact management and other supports,” Dr. Vanessa Allen, chief of medical microbiology at Public Health Ontario, told reporters at a Monday press conference.
Facing case loads of around 300 a day, Toronto Public Health didn’t have the resources to call every person who had been in contact with every case and had to triage to focus on high-risk cases and outbreaks in places like schools, hospitals and long-term-care homes. There were 700 new cases in Toronto and 331 in Peel reported by the province Thursday.
“As the high volume of COVID-19 cases in the city continues, Toronto Public Health’s
case and contact management processes remain streamlined in order for TPH to continue our focus on rapid isolation of cases while performing higherrisk investigations of outbreaks, including workplace outbreaks,” said Dr. Vinita Dubey, associate medical officer of health, in an email.
Asked when full contact tracing of all positive cases would resume, another spokesperson said in an email that the agency will let the media know when that happens.
Peel Public Health “continues to use an expedited case management model to handle the high volume of cases that continue
to persist in Peel,” said the medical officer of health, Dr. Lawrence Loh, in an email, with case managers advising individuals to tell their own contacts to isolate, unless they are considered high-risk.
Simcoe Muskoka District Health Unit, the site of a massive long-term-care outbreak at Roberta Place that was linked to the so-called U.K. variant of the virus, has also “not yet resumed full contact tracing,” said a spokesperson in an email.
The province has added hundreds of new hires to expand contact tracing efforts, committing to bringing the number of staff provincewide to nearly 5,600 by mid-February. And it is rolling out a new tool that uses text messages to connect health-care workers with individuals who have tested positive for COVID-19 or have been identified as close contacts.
Toronto now has more than 900 people on the file. In partnership with the province, 180 contact callers and case managers have been added and an additional 100 case managers are being recruited to focus on rapid isolation of cases, while staff
perform higher-risk investigations, including clusters and workplace outbreaks. Peel Public Health has trained “over 600” staff in the area, and Simcoe Muskoka has added 35 since the start of the pandemic for a total of 47, according to spokespeople.
Chagla recognizes that contact tracing can be an “incredibly time-intensive process.” The use of technology is also key, whether through texts, robocalls or some combination, to find a system that’s “more sustainable” and can quickly reach contacts before they infect others.
“Toronto broke down at 300 cases a day, and Peel broke down at that same amount. You have to have a system that can handle three, four, five hundred,” he said. Even if cases start to drop as more people are vaccinated, contact tracers will still be needed for at least a year or two, to stay on top of small outbreaks, and be ready to ramp up again if needed, he added.
U of T’s Tuite said she’s not sure where the problem lies as the province has added more contact tracers since the beginning of the pandemic. But “understanding the barriers” to why and when it doesn’t work would be helpful.
A recent analysis of contact tracing in 56 U.S. health departments, published by the Centers for Disease Control and Prevention (CDC) found that when individual case loads get too high, contact tracers are unable to keep up. The ideal number seemed to be fewer than 30 patients per investigator. Public engagement and trust is also crucial, the CDC found, and if people hesitate to name contacts the system fails.
In May, New York City hired 1,700 people to join a Test & Trace Corps, a small army of contact tracers, speaking a total of 40 languages. Seven hundred were hired from neighbourhoods hardest hit by the virus, to build trust with residents who might feel intimidated by the government reaching out — something that could be helpful in the GTA, Tuite said.
Countries that have had incredible success containing COVID, like New Zealand, can also offer some lessons. After a recent case in that country was discovered authorities were able to time-stamp and track the woman’s movements through a COVID app and then proactively broadcast to the public that anyone who had been in those places when she was there needed to isolate and get tested.
Of course it’s much easier to stay on top of cases when there are only a handful. But the last thing anyone wants is a replay of last summer, when cases dropped to manageable levels but then slowly crept up again as restrictions were eased, and overwhelmed hot-spot health units, Tuite added.
“It seems like whenever we go into a lockdown situation there’s this assumption that we’re working on strengthening the other aspects of the response, and, at least based on past experience, that hasn’t always been the case.”
“The whole point of lockdown is to give us some time to bring case numbers down and also give us the opportunity to get back on track with testing and tracing.” ASHLEIGH TUITE EPIDEMIOLOGIST