As Canada enters its second month of the COVID-19 crisis, a critical epidemiological and policy question concerns the incidence of this infection in the general population. Estimates of the case fatality rate associated with this virus depend on an accurate count of the number of Canadians who have been or are still infected. Furthermore, determining the number of residents who have already been infected and are now virus-free provides a glimpse into a post-lockdown world, where many Canadians can return to their daily lives in their communities without fear of contracting the virus or spreading it further.
The current published estimate of the number of coronavirus cases in Canada only counts those who have been tested. This represents a small, non-random fraction of the total population.
The World Health Organization estimates indicate that as many as 85 per cent of those infected with COVID-19 experience symptoms that are mild or moderate - not requiring clinical intervention. In addition, new studies suggest that between 25 and 50 per cent of all those infected may be completely asymptomatic.
Given this, how can we know the true number of Canadians outside the hospital system who have been infected with this novel coronavirus? Ideally the answer to this question would be addressed via a large-scale sample survey involving a combination of blood and nasal swab tests. Unfortunately, the technology required to mount such a survey is several months away.
Survey research methods can, however, help to clear some of the fog of uncertainty around the rate of cases in the population by addressing questions regarding COVID-19 symptoms. Put simply - how many households have recently experienced those symptoms most commonly associated with COVID infections? This method is being used with increasing frequency around the world.
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