Failure to test people who might be asymptomatic COVID-19 carriers is missed opportunity, experts say

As Quebec eases pandemic restrictions, infectious disease specialists and other experts say more random testing is needed to find out where the coronavirus is lurking, so that its spread might be halted before it turns into a second wave.

"We've just been relying on putting out the fire," said Benoit Barbeau, a virologist in the department of biological sciences at the Université du Québec à Montréal.

This week, Quebec Public Health Director Horacio Arruda repeated a vow to ramp up testing in the province to 14,000 a day, up from roughly 5,000.

A large proportion of those tests will still be reserved for patients, long-term care home residents and health personnel.

Anyone in the general population with symptoms, particularly those in schools, daycares, factories, construction and first responders, will also be tested.

This makes sense, said Barbeau, but he fears that if the province does not test more broadly — including testing asymptomatic people — it won't have a clear picture of the infection's prevalence in the general population and how rapidly it's spreading.

"What goes under the radar is all the people who stay at home with mild or no symptoms," he said. "Obviously, if you can at least detect people who are infected in certain areas, certain communities, you might have a better grasp of controlling potential outbreaks in these regions."

Dr. David Buckeridge, an epidemiologist at McGill University's School of Population and Global Health, agrees.

New cases will be detected as the province boosts its testing capacity, but many of those will be driven by outbreaks, he said.

"If you're only going into schools where there are outbreaks and testing people, then your proportion of tests that are positive will presumably be very high, because you're validating your prior hunch that someone is infected," he said.

Buckeridge said the Health Ministry should broaden its testing to include asymptomatic people in the general population — people it hasn't previously suspected have the virus.

He admits there are challenges to doing this: first, you have to come up with a way to randomly find people to test. The results will also include false positives.

But if there's a consistent testing strategy, he said, epidemiologists will know how to interpret those results.

More data needed

As Quebec eases restrictions and begins to reopen its economy , this data could help public health officials develop more accurate models to both track and confine COVID-19's spread.

"We want to have an indicator of the epidemic going back up that is as timely as possible," Buckeridge said.

With constantly evolving policies around who gets tested, testing results could not be used to forecast the number of new cases expected in Quebec and demands on the health-care system, said Buckeridge.

Instead, epidemiologists have had to rely on hospitalization data.

The problem with relying on hospital admissions is people tend to go to hospital a week or two weeks after the original infection, so there's a delay in data gathering. These patients also tend to be older and to have an underlying health problem, he said.

"If we have a very well-developed testing policy we understand and we can look at those tests, then we've gained about a week or so in terms of how much more quickly we're going to detect when there's an uptick in the number of infections," he said.

This information could also pinpoint neighbourhoods at risk or certain socio-economic factors that could make people more susceptible to the virus.

"The more we can get a sense, epidemiologically, who is more likely to be infected, in what kind of neighbourhoods, what are those characteristics, the more we can be prepared to be a bit more proactive about how we manage that in the future."

Asymptomatic people not being tested

Earlier this week, Montreal's public health authority announced it is rolling out mobile testing clinics, using city buses.

The clinics will test people with symptoms in so-called hot spots like Montréal-Nord, which has the highest rate of infection on the island.

Once a positive case is identified, public health investigators track down everyone that the infected person might have been in contact with at work, at home or in their neighbourhood. That's what's known as contact tracing.

Dr. Paul Le Guerrier, an infectious disease physician with Montreal public health, said depending on the complexity of the case, teams are able to investigate about 350 to 400 cases a day.

Each and every person that may have come into contact with a positive case is called.

But if the contact is asymptomatic, they probably won't be tested for COVID-19, said Le Guerrier.

"If we put them in isolation and they have no other contacts, then it might not be worth testing them. So we can take that test and try to test someone else where we might be able to identify other contacts and place these other contacts in isolation," said Le Guerrier.

But that's a missed opportunity, said Dr. Cecile Tremblay, an infectious disease specialist at the Centre hospitalier de l'Université de Montréal.

Even if someone has no symptoms, that person might be a carrier and can infect others, she said.

"This approach isn't totally random," said Tremblay. "So you have an indexed case and you test all of their contacts, even if they aren't symptomatic."

Having a good understanding of how that one indexed case contaminated other people is useful, she said.

A spokesperson for the Ministry of Health, Marie-Claude Lacasse, said increased screening will identify outbreaks at the local level more quickly.

She said detection capacity will be increased in the coming weeks.

Random screening of asymptomatic people will not be done in the short term, she said in an email, but it is being considered "precisely for this purpose in outbreak contexts or for the follow-up of close contexts in a more systematic way."