Supporting Ontario’s Health System with Epidemiology and COVID-19 Data Resources


5 March 2021

Epidemiology is a cornerstone of public health practice and essential to the COVID-19 pandemic response. We have been constantly learning about COVID-19 since it first emerged at the end of 2019. As the situation progresses, we continue to gather data to inform decisions about containing the disease and helping to keep people healthy and safe. Epidemiology is key to the response, as it involves studying the data to help us understand:

  • Who is most affected
  • Where they are in the province
  • When were they exposed

"Having information about those factors is essential for both local and provincial decision-making and for the public to understand the situation."

— Karin Hohenadel, Manager, Communicable Diseases

Public Health Ontario (PHO) has a longstanding history of transforming data into interactive tools and resources to help provide an overall picture of what’s happening in the province. As the pandemic has evolved, so too have our health system partners’ data needs. PHO’s COVID-19 epidemiological products include:

  • the daily epidemiological summary – provides an epidemiological summary of recent COVID-19 activity in Ontario and shows trends compared to the previous day 
  • the weekly epidemiological summary – highlights cases over time, characteristics of cases, deaths, exposure, and sub-populations of interest
  • the interactive Ontario COVID-19 Data Tool – provides cumulative COVID-19 information at the provincial level and allows users to explore and get more information about their local health unit
  • enhanced epidemiological summaries – provide focused analysis on topics of interest

Digging deeper into the data

The interactive Ontario COVID-19 Data Tool allows users to look at provincial level information as context and drill down to the local level to see what’s happening. 

"One of the main reasons for developing the tool was to offer users with more information that a static PDF doesn’t easily provide. In our online PDF almost everything is aggregated up to the provincial level. The tool allows users to slice, or focus or extract data on a specific region. If users need to pull something out quickly, they can take an image or copy of the data from the tool itself"

— Brenda Lee, Epidemiologist Lead, Knowledge Services

The tool can potentially be used for hypothesis generating and a starting point for doing more in-depth analysis. “We often take a broad look first that inspires us at the provincial level, as well as at the local level to take a deeper dive and understand what we’re seeing in the tool with more depth. We’ll often go and look for age variations, geographic variations and other types of interesting information,” said Hohenadel.

"Everybody is so busy responding and getting out the daily information that decision-makers need, however it’s always important to step back and think of some key areas where we want to explore the data further. We decided that it would be helpful to look more in depth at some specific aspects of the pandemic, which is why we decided to do some enhanced summaries."

— Dr. Shelley Deeks, Chief Health Protection Officer

For example, PHO’s analysis on severity looks at outcomes by age as well as comorbidity. The data show the proportion of hospitalizations, cases treated in ICU, and deaths was higher among cases reporting at least one medical comorbidity (23.5%, 6.1% and 11.7% respectively) compared to those not reporting any comorbidities (8.9%, 1.7% and 7.1% respectively).

Another example is in the COVID-19 in Long-Term Care Home Residents report, which shows that LTC home residents had a higher overall and age-specific case fatality, but a lower risk of hospitalization or admittance to ICU than persons of the same age not residing in LTC.

How this disease impacts children is another area we are continually learning about, which is why PHO chose to focus an epidemiological summary on children. Table 1 in the summary shows that among cases in children, rates of illness were highest among those 15-19 years of age. “That’s not necessarily typical that 15-19 year olds have higher risk of the disease than 10-14 year olds,” said Deeks. “One importance of an epidemiological report based on the data is it can lead to hypothesis generation and you can look to other forms of study to learn more about an issue.”

“When we don’t take the time to look at the data in critical ways, I think we actually miss opportunities to learn from this pandemic,” said Deeks. “Everybody’s so busy responding, we’re getting so much data in and the response is critical, but it’s really helpful to be able to look at the data and look to see what it’s telling us and if we’re looking at it in a way to maximize its utility.”

Addressing evolving data needs

PHO’s general epidemiology strategy continues to adapt to meet the need for different types of data analysis as the pandemic unfolds. For example, at the start of the pandemic the focus was primarily on travel-related cases and contacts before changing focus to long-term care homes and other congregate settings. Recently, PHO began a COVID-19 serosurveillance initiative, which uses antibody testing to better understand what proportion of the Ontario population has COVID-19 antibodies and to identify regions and age groups within the province with higher antibodies. The COVID-19 Serosurveillance Summary will enable the public health system and the government to evaluate the effectiveness of the pandemic response so far, and take targeted steps to prevent further spread of COVID-19. 

“What’s really interesting is seeing the way the pandemic has evolved and the way our data needs have evolved with it,” said Hohenadel. “We’re always trying to both catch up with and anticipate what the next data and information need will be for those in the health system.”

Visit PHO’s COVID-19 Data and Surveillance page for the latest COVID-19 enhanced epidemiology summaries and surveillance reports. 


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Updated 5 March 2021