The Difference Between Epidemics And Pandemics

By Debra Kelly on Thursday, January 9, 2014
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“Now here’s an interesting person. Apart from being a full-time stapling machine, he can also give a cat influenza.” —Monty Python’s Flying Circus, “Interesting People”

In A Nutshell

Both epidemics and pandemics are widespread illnesses, but which is cause for more alarm? When a disease is epidemic, it spreads quickly through the population of a specific area. When a disease goes pandemic, that means it’s spread globally.

The Whole Bushel

It seems as though a new virus or disease rears its ugly head every year. Avian flu, swine flu, and seasonal flu . . . no matter how many vaccines we develop, it seems as though the germs are one step ahead of us. We often hear terms like “epidemic” and “pandemic” when health officials start talking about precautions we need to take and how widespread an outbreak will be, but what do they really mean?

What designates an epidemic depends on what disease or illness is being talked about. The threshold of an illness being elevated to epidemic status is dependent on what’s normal for the illness, the area, and the time of year. For example, an outbreak of influenza becomes epidemic when the number of people who get sick rises above what it was in previous years and spreads quickly through people. Epidemics usually occur within a certain geographic range, whether it’s an entire country or region.

The outbreak becomes a pandemic when the number of ill people begins to skyrocket. When the disease spreads outside of its original zone of influence, it’s said to be turning pandemic. A pandemic illness will often spread across the entire planet.

Generally, epidemics and pandemics are caused by a different type of germ or virus strain. Most epidemics are caused by a strain that regularly circulates through a population. Because many people have at least some type of immunity to it already, the illness will not be as severe or spread rampantly through entire populations. Pandemics often occur with the appearance of a completely new strain of virus or bacteria. Without previous exposure to the illness, there is little to no natural immunity to the disease and people are more vulnerable to its effects and spread. New strains often occur when a virus makes the jump from animals to humans, or when it undergoes an antigenic shift. This shift changes the protein makeup of the flu virus, and renders existing vaccines and immunities useless.

Traditionally, influenza pandemics have happened about three times in every century since the 1500s. In the most extreme cases, these worldwide outbreaks can be responsible for the deaths of millions; in the winter of 1918–1919, the Spanish flu killed between 40 and 50 million people. More recent pandemics have also been extremely devastating. A pandemic of Asian influenza killed two million people in 1957.

While epidemics can still be quite severe, they’re generally on a smaller scale. In 2003, one of the worst epidemics in a long time, the severe acute respiratory syndrome (SARS), was determined to be the cause of the death of around 800 people.

The World Health Organization has several charts with which to map the progression of disease outbreaks. The influenza pandemic alert system has six phases, outlining stages starting with the presence of a new flu virus present in animals to confirmed outbreaks in more than one country. The Centers for Disease Control and Prevention also has a Pandemic Severity Index for tracking the estimated death tolls in a pandemic situation. Ranging from Category 1 to 5, a Category 5 outbreak means that more than 2 percent of those who fall ill will die.

Show Me The Proof

Centers for Disease Control: An Introduction to Epidemiology
Medical News Today: What is a pandemic? What is an epidemic?
CDC: Resources for Pandemic Flu