The Chief Public Health Officer of Canada, Dr. Theresa Tam, has indicated that there is cautious optimism that the COVID-19 epidemic is slowing down. From Dr. Tam’s pan-Canadian view of the progression of the epidemic, Canada is on the right track.
Below is a chart describing the progression of the COVID-19 crisis across Canada.
The blue and red lines show the total number of confirmed cases as well as the daily increase in cases respectively and are plotted on a logarithmic scale (right). The green lines show the rate of growth in the number of cases with the thin green line shows the ratio of growth as a function of new cases that day vs. the number of cases the day before; a number less than 1.0 means that the number of new confirmed cases that day was less than the day before. The thick green line shows a weighted average of the daily growth ratio in order to better derive the trend.
Since the 5th of April, the trend across the whole of Canada has been one of a stabilized number of new cases being confirmed each day; an average of 1,259 cases a day. This is consistent with what the growth ratio demonstrates as it approaches the all important 1 line representing one new case confirmed based on the previous day. This, however, does not mean that the country can return to normal.
Comparison to South Korea
To understand the conditions that may need to be present before Canadians start to see an easing of physical distancing restrictions we can look to South Korea which, because of a combination of institutional and cultural differences, has been able to more quickly manage their COVID-19 outbreak.
On the 18th of February South Korea saw a surge in confirmed COVID-19 cases as a result of a well documented Super-Spreader event that saw their daily newly confirmed case numbers rise from an average of just over 1 per day prior to that date to an average of more than 388 per day during the week of the 23rd of February. Because of the low numbers involved initially, both the daily growth ratio and the averaged growth ratio spiked – literally off the chart – but by the 29th of February South Korea was experiencing an averaged growth ratio of 1.368. Continuing efforts saw the averaged growth ratio continue to decline until the 7th of March when it decisively dipped below the 1.0 mark marking the levelling off and subsequent decline of their outbreak.
As a side note, it is important to understand the way that the logarithmic scales used with some in the charts tend to skew the way the data is presented. The chart below compares the total number of confirmed cases for Canada and South Korea using a logarithmic scale (red) and a linear scale (blue).
While the scale of the outbreaks in Canada and South Korea differ greatly, the shape of the resultant charts will closely align and follows a logistic curve. The process of tracking the ratio of growth allows us to understand where on the curve we reside and whether the outbreak is waxing or waning.
In terms of the overall shape and position of the outbreak, Canada is now approximately where South Korea was on March 3rd; at a point of inflection, possibly at the crest of the wave with the decline in sight or possibly still at a point of stabilized growth. About 3 to 5 more days of data is required to conclusively say whether the country has crested the wave or not.
British Columbia was the early epicentre of the COVID-19 outbreak in Canada, likely due to its proximity to Washington State which was the site of the first documented cases of community spread in North America. It has been seeing an overall decline in the growth of its newly diagnosed cases, even seeing the averaged growth ratio dip beneath the all important 1.0 mark for two days at the beginning of April. That decline in growth is indicative of a 3 week trend in properly managing COVID-19 within in the province and may demonstrates a suitability for a relaxation of physical distancing measures if and when a fast and reliable testing method comes online. However the return of the averaged growth to the greater than 1.0 area on the 6th of April is a sign that the stability seen in the chart is tenuous and susceptibility to a Super-Spreader type event as witnessed in South Korea remains high.
The Prairies provinces saw a slow and steady rate of growth through the month of March with a peak of growth within the first week of April. That first week also saw a false decline on the 4th of April, and may demonstrate why before consideration of a reduction in physical distancing is considered there should be a demonstration of multiple days of the averaged growth ratio staying beneath the 1.0 mark. Of concern is a recent resurgence of growth, primarily driven by cases identified in Alberta, driving the averaged growth ratio well above the 1.0 mark. Saskatchewan may be in a position, with a fast and reliable testing method coupled with a concerted contract tracing regime, to move away from strict physical distancing measure.
Ontario has yet to bring its averaged growth ratio beneath the 1.0 mark for a single day since March 5th, a time when the province had reported only 22 confirmed cases. In recent days the averaged ratio of growth has seen a sustained downward trajectory but at least a week of data is required to properly ascertain whether it will be in a position to begin to realistically begin to implement measures to relax physical distancing.
The averaged growth ratio in Quebec has only touched the less than 1.0 mark on a single occasion – April 9th – since the outbreak exploded there. While recent trends has seen a slow and sustained decline in the averaged growth ratio, as with Ontario at least an additional week of data is required to properly ascertain whether this is a sustained trend that could eventually lead to relaxing of physical distancing.
The four Atlantic provinces collectively have the lowest number of confirmed COVID-19 cases of all of the regions outlined here and because of that have the noisiest signal from which to ascertain a trend. There have been multiple occasions when the averaged growth ratio has dipped below the 1.0 mark, but a small number of newly identified cases has caused a hard lurch back into the greater than 1.0 territory. Nova Scotia is the primary driver of the recent surge in cases, causing the averaged growth ratio to be decidedly positive for the last week. As with British Columbia and Saskatchewan, assuming a fast and reliable testing method soon comes online, the remainder of the Atlantic provinces could begin to relax physical distancing measures.
There is reason for cautious optimism in select parts of Canada. The data indicates that fully half the provinces across the country – British Columbia, Saskatchewan, New Brunswick, Prince Edward Island, and Newfoundland – may be in a position to soon relax some physical distancing measures and move to a containment approach over the mitigation approach currently employed should a fast and reliable testing method become available.
Data used in this post can be accessed here.
Feature Image by Felipe Esquivel Reed; Image obtained from Wikimedia.