Every day, Dr. Deena Hinshaw updates Albertans on the number of COVID-19 cases in the province, the number of fatalities, hospitalizations and recoveries.
Alberta’s chief medical officer of health provides these daily statistics with a calm, level demeanour, and then answers questions about the province’s situation and its public health response.
Sometimes, she’s asked things like, “How is Alberta doing?” or “How does Alberta’s response compare to other regions?”
The numbers can be overwhelming, but questions like those are even harder to answer. Provinces are responsible for the delivery of health care, and have taken different approaches to their COVID-19 response and testing.
Their populations, rates of testing and methods of reporting confirmed cases also make it difficult to even try to compare and contrast.
Factors to consider
Dean Eurich, a clinical epidemiologist with the University of Alberta’s School of Public Health, says there are many factors behind the number of cases observed in each province, including population size, testing rates, sub-groups within each province that are being targeted for testing, each province’s definition of a COVID-19 case, and its reporting structure.
“Cross-provincial comparisons are very difficult to make because of all these factors,” Eurich said.
Context is everything
While Hinshaw does include hard numbers in her daily updates — like confirmed cases, fatalities, hospitalizations, lab tests completed and recoveries in the last 24 hours — she also provides background and answers questions.
She’s able to put into perspective how Alberta’s higher rate of testing results in a higher number of confirmed cases, for instance.
“I know seeing this increase in numbers may be a concern to some,” Hinshaw said during her update on April 13. “But, it’s important to remember that the number of daily confirmed cases as a percentage of the tests done every day has remained approximately similar through the past several weeks … approximately two per cent.”
“Another thing we look at is the rate of hospitalization, which is currently a more accurate indicator of the trend than our total case numbers.”
“This is because our total case numbers are determined by our testing eligibility, which has changed over the last 10 days.”
Alberta Health spokesperson Tom McMillan added that the figures reported at Alberta’s daily updates are just one part of the information provided.
“Dr. Hinshaw is providing daily updates, discussing the situation in Alberta and explaining what this means for our province and how Albertans can protect themselves and those around them.”
How we define a COVID-19
Reporting structures and case definitions have changed even within the same province over time.
“In the early days, many provinces reported cases as only those which were laboratory-confirmed,” Eurich said. “Now … most, if not all, are reporting both laboratory-confirmed as well as presumptive cases in their totals.”
When a province starts including presumptive cases in its total, the number of cases increases.
If a province changes its reporting structure, Eurich said, that can also lead to a big jump.
“On April 1, a large spike in cases in Ontario was observed,” he said. “There was a change in the data collection methods whereby Ontario data is now collecting from individual public health units to improve the accuracy and timeliness of updates.”
Alberta Health always included both probable and confirmed cases in the total number each day, McMillan said. But, to be as transparent as possible, it started breaking the two down in early April.
Alberta Health believes reporting the daily confirmed cases is still incredibly valuable.
“In any illness, there will always be cases that aren’t detected within the province. However, that does not change the importance of the information being reported,” McMillan said.
Another factor to consider is each province’s rate of testing, lab capacity and speed. Eurich said those vary quite a bit between provinces.
“In all provinces, the cases reported are rarely in real-time and reflect cases that occurred several days prior,” he said, adding Alberta’s turnaround rate is higher than other provinces, like Ontario, which is seeing more delayed results.
“So, if one were to look at a snapshot of cases today across each province, the time period that is actually reflected in these numbers is unlikely to be the same, making comparison more difficult.”
Alberta has been turning around lab test results between 22 and 24 hours, the province said.
Alberta has been completing about 2,000 tests per day for the last few weeks. Hinshaw said Alberta has the lab capacity to complete an average of about 7,400 tests daily and is aiming to have up to 9,000 tests completed a day by the end of the month. By mid- to late May, the goal would be 20,000 tests a day, using a combination of blood tests and swabs, McMillan said.
“Alberta is doing the most testing per capita of any jurisdiction in North America.”
“That means we are capturing and reporting as many cases as possible. We are giving Albertans the most accurate picture available of COVID-19 in the province, and every confirmed case is another opportunity for us to limit the spread in Alberta and save lives, McMillan said.
“Our goal is to protect Albertans from COVID-19. The information also reflects the work that is being done.”
The data allows Alberta Health to diagnose and treat those individuals at greatest risk of severe outcomes, trace the spread of the virus, and identify what steps are needed to help limit the spread, he added.
“It also provides accurate information about the effects our public health measures are having and help us determine if we need to take further steps.”
Eurich echoes that the main purpose of Alberta’s testing isn’t to track case numbers and follow the spread in all communities. Instead, he says the priority is having enough information to plan a health response — identifying the really sick people, providing them care, improving the response to protect health-care workers and making sure the system as a whole can respond.
“This is why testing criteria have changed so much on an almost day-to-day basis in the provinces: to ensure that our testing is appropriately deployed so that governments can mount the best response possible to the pandemic.
“When one understands that testing is really about this key concept to ensure the highest level of response, one can better understand why criteria for testing have changed and also how this obviously impacts the cases observed on any given day.”
Who can even get a COVID-19 test in the first place varies from province to province.
On April 13, Alberta expanded eligibility to include anyone in the province with COVID-19 symptoms, but this broad testing is rare. Other provinces are only testing people who meet certain criteria, like recent travellers, or who exhibit several of the listed symptoms, or who belong to a specific demographic.
Eurich said it’s more helpful to hear the total number of tests processed and the cumulative per cent of positive tests over time.
Hinshaw said April 13 that Alberta’s rate of positive tests has remained fairly consistent at about two per cent for the last number of weeks.
“This indicates that the rate of infection has remained relatively stable over the last while,” she said.
Eurich points out that Alberta changed its testing eligibility, and recording and noting when exactly those changes took place will help better interpret the data.
Hinshaw acknowledged Monday that expanding testing capacity would naturally lead to more confirmed cases.
“We will see a further increase in the number of cases confirmed each day as a result of this testing. We have already seen this increase over the past few days with the expansion we’ve already done.”
She said Albertans shouldn’t focus on the case number, but rather the percentage of positive cases out of all people tested and the rate of hospitalization.
Tracking COVID-19 deaths
Some experts feel tracking the number of fatalities due to the virus — and the trend of that statistic — provides a more accurate picture.
“One of the best ways of estimating the true case rate is to use the confirmed COVID fatalities for a given jurisdiction (province, country, state, etc.) and to use the incident or case fatality rate (IFR or ICR),” said David Wishart, professor in the University of Alberta’s Department of Biological Sciences, Department of Computing Science, and Department of Laboratory Medicine and Pathology.
“This corrects for the under-testing, asymptomatic cases or differential testing problem between jurisdictions.”
Wishart was also part of the U of A team that created the COVIDmapper webserver. The online tool uses several algorithms to pull and process information from different resources, including the World Health Organization, governments and post-secondary institutions across the world, to better assess the impact of the pandemic.
“The likely number of COVID cases is typically five to 10 times the number of COVID cases reported,” Wishart added.
Potential asymptomatic cases
Health officials across Canada acknowledge that asymptomatic spread may be more common than initially believed. So far, provinces have not begun testing asymptomatic individuals for COVID-19. Therefore, the true number of cases in a population may never be accurately represented.
Eurich said that’s why public health authorities have stressed the importance of physical distancing and staying home as much as possible, even if you feel well, to reduce the possible transmission by everyone, including asymptomatic people.
“It will be many months, or even years, before we know the true extent of the COVID-19 infection rate in Alberta and Canada.”
“We are deploying all of our resources in what is termed ‘the high-risk’ approach, whereby we are trying to identify those that are symptomatic (to prevent spread and break this transmission of known cases) or at high risk of poor outcomes … or at high risk of crippling our ability to manage cases (i.e. healthcare workers).”
Hinshaw said Tuesday that while some countries have tested people who don’t have symptoms, Alberta’s strategy has been to focus on those who are the highest risk of transmitting.
“We were able to expand our testing eligibility to anyone across the province who is experiencing any symptoms related to COVID-19,” Hinshaw said. “If we do have capacity in our lab leftover after we’re able to do all of that testing for all symptomatic Albertans, then we can consider testing those who do not have symptoms.”
Still, she pointed out that testing people without symptoms provides only a short snapshot in time.
“A negative test in someone who’s asymptomatic does not mean for sure that they haven’t been exposed to the virus.”
“So, again, testing asymptomatic people would be an additional layer that we would put on top of our current testing protocol should we have the capacity to do so. And we’re currently discussing where strategically might be the best place to utilize that capacity.”
Hinshaw also said other countries have found that people who are at one point asymptomatic and test positive for COVID-19 usually do exhibit symptoms at some point.
The numbers are still valuable
The data is still informative, Eurich said, especially if you can take a step back and look at overall trends for each province without trying to compare the numbers too much.
“We can get a sense of the trajectory of the cases and where each province may be heading in terms of COVID-19 cases and potential resource requirements,” he said.
Eurich said he’s less focused on the total number of cases on a given day and more interested in the change in the trajectory of cases.
“It is critical we flatten the curve to ensure our health-care system and workers can manage the COVID-19 cases.”
“So, although the total cases may not be a complete picture of the true underlying caseload within a province, the change in cases and the trajectory of future cases does provide important insight on the resources that are going to be required to manage the pandemic.”
In the future, when more resources are available, he expects Canadian provinces to use a multi-pronged approach to survey the population that will include testing the blood of people who had mild symptoms to see if they have antibodies for COVID-19.View link »