The challenges of contact tracing
Problem is not only recalcitrant citizens
TORONTO — When Ontario publichealth nurse Joanne Alessi phoned Dean Macauley this month to tell him he’d been in close contact with someone infected with COVID-19, the call did not go well.
Alessi’s Haldimand-Norfolk publichealth unit required Macauley to quarantine for two weeks, but he refused to do it unless he tested positive for the coronavirus himself, according to a provincial appeal tribunal’s recent decision on the case.
Then he abruptly hung up on the nurse.
A legal quarantine order was issued, which the man vowed to ignore as he travelled to and from Quebec. He also appealed the directive, questioning in part whether the pandemic actually existed. The tribunal upheld the public-health order last week.
The nurse was doing what’s called contact tracing, considered crucial to taming COVID-19 and avoiding another devastating lockdown, at least until there’s a vaccine or effective treatment. But the Macauley case underscored just how challenging that task can be.
And the problem is not only recalcitrant citizens.
Tracing those who have had contact with coronavirus cases can be invaluable, but it has to be done rapidly and thoroughly to be of any use, says a new review of past studies.
If it takes more than four or five days from the index case developing symptoms to their contacts being ordered into quarantine – thus allowing the infection to spread further afield — the effort may be all but pointless, concluded the study by University of Montreal and affiliated researchers.
In the epidemic’s first few months, in fact, Canadian authorities often waited several days just to obtain a test result on a symptomatic patient, let alone find contacts.
“If you don’t do it well, if you do it with long delays, the contribution will be very small,” said Carl-Etienne Juneau, co-author of the review paper. “Once people start having symptoms, you have to act very quickly.”
Contact tracing has become a bit of a holy grail in the fight against COVID-19, with countries such as South Korea, Singapore and Taiwan demonstrating that doing it aggressively can avoid having to keep everyone at home for months on end, with disastrous economic effects.
Vancouver Coastal Health recognized its importance, and the need to do it fast, early on, too, says Dr. Patricia Daly, the region’s chief medical officer of health. Her department ramped up at the peak of the epidemic from 12 tracers to 270, and has been able to get to almost all contacts of an infected person within 24 hours of a positive test, she said.
“It doesn’t always seem exciting, but it may be the most important thing we’re doing to control COVID spread,” she said in an interview. “In my opinion, the difference between what’s happened in the U.S. and Canada is two things: better access to testing here, and very good follow-up of cases and contacts.… That’s what’s flattened the curve here in B.C.”
Juneau, a public-health PhD who works for Montreal public health, and colleagues at the University of Montreal found 32 observational and modelling studies on contact tracing for COVID-19. They were not the most rigorous type of research, but 30 of them concluded the measure is an effective way to contain an epidemic, said the paper, which has yet to be peer reviewed.
All the modelling studies, for instance, concluded that if done well and rapidly, “you could stop the epidemic just with contact tracing,” Juneau said.
But what does that mean, exactly? Based on the studies reviewed, his paper concluded that officials need to find 80 per cent of a case’s contacts within two to three days of the person developing symptoms.
If tracing takes more than four or five days and/or finds fewer than 60 per cent of the contacts, it “may not contribute meaningfully to control of COVID-19.”
After delays earlier in the pandemic, it seems at least some Canadian jurisdictions are meeting those contact-tracing deadlines now.
The public-health department of Peel region west of Toronto said it typically manages to reach contacts within 24 to 48 hours of a case being identified.
At the peak of the pandemic the unit had 237 staff doing contact tracing, though that number had dwindled to 190 by the end of June, said a department spokesman.
When someone defies publichealth authorities, though, the process stalls.
Haldimand-Norfolk, a largely rural area southwest of Toronto, has had to issue isolation orders in 100 cases out of about 4,000 people it’s asked to quarantine through contact tracing, said the recent decision by the Health Services Appeal and Review Board.
Macauley couldn’t be reached and the health unit did not respond to requests for comment, but the ruling offers a unique glimpse into how the system works, or in this case did not work.