An oft-cited phrase in pandemic disease planning is that it's not a question of "if," but "when."
There are countless epidemics around the world and some of these can become pandemics, a somewhat loosely defined term for an outbreak that is present in several regions around the globe at the same time.
There was the H1N1 pandemic in 2009, and the world is still battling HIV/AIDS. In 2011, 34 million people were infected with HIV/AIDS and 1.7 million people died, according to UN statistics.
However, health experts say worrying about a future pandemic just isn't worth it.
"Allowing it to have some substantial degree of control over your life, if you're not in public health care, really doesn't make any sense," said Dr. Allison McGeer, director of infection control at Mount Sinai Hospital in Toronto.
"On the scale of things you're likely to die from, it's really not up there."
McGeer herself contracted Severe Acute Respiratory Syndrome (SARS) in 2003, as did dozens of the thousands of health-care workers who worked to halt the outbreak.
Although it never reached pandemic proportions, SARS still clogged Toronto hospitals and strained the province's health-care system.
Many consider SARS to have been a global wake-up call for disease planning. A number of government commissions in Canada highlighted weaknesses in the public health system while also lauding the hard work of medical staff.
In the wake of SARS, the federal government created the Public Health Agency of Canada to mount a coordinated, effective response to infectious disease outbreaks. It also appointed Canada’s first-ever public health officer.
'Host of ways' for diseases to spread
Health officials often cite influenza as a likely source of future pandemics. Seasonal outbreaks kill between 250,000 and 500,000 people worldwide every year, according to the U.S. Centers for Disease Control.
There have been four influenza outbreaks in the last 100 years — including the 1918 Spanish flu, which killed at least 40 million people — and they are usually spread through coughing and sneezing.
Other potentially deadly diseases can also be spread through waterborne-transmission or by animals, said Michael Gardam, director of infection prevention and control at the University Health Network in Toronto.
"There is a whole host of ways that these things can spread around," said Gardam, who served as director of infectious diseases at Public Health Ontario during the H1N1 pandemic in 2009.
How deadly a disease is, along with human crowding and a population's previous exposure to it, are key factors that determine the impact of a particular outbreak, Gardam said.
"There are multiple things that come into play and [that's] one of the reasons that it is so hard for epidemiologists to actually predict what's going to happen with something," he said.
How easily it can be spread from person to person will also affect outcomes, because that will determine whether a coughing person infects one person or 10.
"Some viruses are very, very good at that," Gardam said. "It takes a very low infectious dose to [infect people] and other viruses, like SARS, by and large, it just takes a lot more of that to do that."
Another crucial factor is how long a person remains infectious. The actual route of transmission — for example, fluid transmission during sexual contact or a blood transfusion — can also affect the spread of a disease.
"A sneeze is much more likely to infect 10 people than HIV," said Eleanor Fish, a professor at University of Toronto's immunology department.
Much of the battle against future pandemics involves monitoring outbreaks around the globe, a task that largely falls to the UN's World Health Organization. The WHO then updates public health officials in individual countries.
Currently, it has been monitoring a new, SARS-like corona virus with a total of 16 confirmed cases and nine deaths, mostly in Saudi Arabia.
There have also been a cluster of cases in the U.K., but the WHO's update on March 23 says that it appears that it is not easily transmitted between humans.
Part of the WHO's job is to monitor influenza viruses that are primarily being passed from animals to humans, which is a fairly low risk in terms of the spread of a disease.
SARS, for instance, originated in bats, but made the jump to humans through civet cats, which were available at markets in China, before it started passing between people.
"With flu-like viruses, as soon as there is human-to-human transmission, that is something we need to be worried about," Fish said.
Shouldn’t lose sleep over pandemic fears
Although the timing and severity are hard to predict, previous evidence suggests that a flu outbreak somewhere in the world would likely reach Canada within three months, according to the Canadian Pandemic Influenza Plan, which was also created in the wake of the SARS crisis.
This would likely create several waves of infection, each lasting between six and eight weeks, over the course of a 12- to 18-month period.
One of the best tools for stopping a pandemic would come in the form of a vaccine, if it were available or could be created quickly, McGeer said.
"You protect people so they are not susceptible," she said, adding that this is the method for controlling measles in large parts of the world.
Public health officials can also rely on education plans to encourage people to wash their hands or even recommend people avoid crowded areas in the event of a serious viral outbreak.
Public health officials can also attempt to prevent the spread of a disease by isolating those who have been infected and quarantining people who may have been exposed to see if they become ill.
One of the biggest stumbling blocks to disease prevention, McGeer said, is that human brains just don't seem to be wired to think ahead.
"It always looks like something in the future — there are always more important things to invest in," she said.
McGeer said investing, and maintaining investments, in pandemic disease planning is like buying insurance.
"At an individual level, nobody should be losing sleep over [the fear of a pandemic], but it shouldn’t stop you from a really clear understanding that we need a strong public health system precisely because it will protect when the next pandemic comes."
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