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Infectious disease outbreaks: from The Plague to COVID-19

A century ago, after the 1918-1919 “Spanish” influenza pandemic, few Canadians had to be reminded about how deadly a respiratory viral infection could be.

A century ago, after the 1918-1919 “Spanish” influenza pandemic, few Canadians had to be reminded about how deadly a respiratory viral infection could be. Estimates vary, but 50 million to 100 million people worldwide perished in the most devastating pandemic in history – an event that, strangely, has largely receded from memory.



Older people will also remember the polio epidemics. “The Crippler” left in its wake close to 50,000 children, as well as adults, with varying degrees of muscle weakness and paralysis, and over 4,100 dead. These worsened across Canada from the late 1920s through the late 1950s during the years before polio vaccines were widely available.


During the 1980s and 1990s, HIV spread rapidly around the world. Acquired Immune Deficiency Syndrome (AIDS) was lethal until the development of treatment regimes, public education campaigns and other prevention measures.


 In 2003, thousands of people fell ill, and many died, during an especially severe outbreak in Toronto that seemed to target hospitals and health care workers. This was “SARS” (Severe Acute Respiratory Syndrome), a pneumonia-like infection caused by a novel coronavirus (similar to COVID-19) that began in China and was imported into Canada.[3]


But until the COVID-19 pandemic contemporary urbanized societies were no longer especially preoccupied with the threat of widespread infectious disease outbreaks. While this prevailing sense of security is rooted in genuine confidence in public health protections and medical science, it also reveals a kind of social complacency and amnesia about the damage that infectious diseases are capable of inflicting.




Among all of these earlier examples, the “Spanish” influenza pandemic was unique in its intensity and extent. Its story also offers powerful insights into the impact and aftermath of the COVID-19 pandemic. We understand much more today, but our well-being still depends not just on science, but also on a broad and deep understanding of the stories of past tragedies.


During the Middle Ages and through the 19th century, urban populations in much of Europe and Asia were regularly decimated by pandemics. Bubonic plague was one of the most deadly diseases, transmitted by fleas and parasites. According to the World Health Organization, the bubonic plague – also known as “The Black Death” – killed about 50 million people in 14th century Europe and continued to circulate for centuries.


Later on, the conditions of urban life as well as mass migration became key factors driving the rapid spread of highly infectious and deadly diseases such as smallpox, typhus and cholera. Successive epidemics of cholera swept through Europe and spread to North America on ships filled with migrants from Britain. In Canada, cholera arrived in the 1830s and triggered health emergencies in cities like Montreal and Toronto, prompting unprepared authorities to establish the earliest public health boards.


At the time no one knew how most infectious diseases spread from one individual to another. Scientists hadn’t yet discovered bacteria or viruses (“germs”), the microscope hadn’t been invented and the concept of vaccination was in its infancy. Colonial governments enacted draconian quarantine laws, but these often failed to be enforced by local officials.



A turning point in the containment of infectious disease outbreaks occurred during a cholera epidemic in London, England, in 1854. Tens of thousands of Londoners had died of cholera epidemics in 1849 and 1853. During an 1854 cholera outbreak, a young physician named John Snow came up with the idea of mapping the addresses of victims in a west-end neighbourhood centred on Broad Street. When he analyzed his famous “ghost map,” he realized that many of the sick and dead lived close to an outdoor water pump that drew on a well contaminated by a nearby privy. Snow’s empirical observations, considered to be among the first breakthroughs of modern epidemiology, prompted local officials to remove the handle on the Broad Street water pump, a turning point in public health policy.


During the late 19th and early 20th centuries, many public health advocates and governments pushed to implement prevention-oriented improvements geared at limiting the spread of diseases. The mass production of vaccines and the advent of large-scale inoculation campaigns shifted the fight against infectious disease and epidemics into the realm of preventative medicine.


Routine vaccinations have become one of the principal prevention measures against a range of infectious diseases. Smallpox was declared eradicated from the globe in 1979, and polio is close to the same goal.


What are the connections between today’s national and global public health practices and the pandemic that ravaged so much of the world in 1918? Epidemiologists today understand more about the vectors of infection because they’ve examined how pandemic influenza spread from troops traveling to and from European battlefields. We drew on some of these lessons during and after the SARS pandemic, in 2003, although dramatic evidence that’s surfaced during the COVID-19 pandemic — about critical shortages of medical supplies and equipment — reveal what can happen when shocking events recede from memory.



The Defining Moments Canada website provides a wealth of information about the way Canadians were affected by this pandemic.


Our goal is inoculate ourselves from the lethal consequences of collective amnesia. We seek to remember not just for its own sake, but to ward off the complacency that can leave our communities vulnerable to, and ravaged by, future epidemics.


John Lorinc is Senior Editor, Defining Moments Canada

Excerpted from Defining Moments Canada, published March 30, 2020.