Epidemics/Pandemics – Introduction

Visit Flu.gov for Latest Info[4]

When is a disease outbreak a concern? And what is the difference between an epidemic, pandemic, or the plague? Learn the basics about the spread of serious diseases and what you can do to protect yourself, your family, and your community. Occasionally, the amount of disease in a community rises above the expected level.

  • Epidemic refers to an increase, often sudden, in the number of cases of a disease above what is normally expected in that population in that area.
  • Outbreak carries the same definition of epidemic, but is often used for a more limited geographic area.
  • Cluster refers to an aggregation of cases grouped in place and time that are suspected to be greater than the number expected, even though the expected number may not be known.
  • Pandemic refers to an epidemic that has spread over several countries or continents, usually affecting a large number of people.
  • The generic “plague” has entered the language as a descriptor for any deadly epidemic disease.[1]

Epidemics or pandemics have had a remarkable place in history and enormous effects on the development of modern civilization. Some scholars have even suggested that the collapse of the Roman Empire may be linked to the spread of plague by Roman soldiers returning home from battle in the Persian Gulf in 165 AD. Below are some figures of deaths from epidemics or pandemics:

  • Smallpox (1350 BC – 1979) – 500-900 million
  • Spanish Flu (1918 – 1919) – 50-100 million
  • Black Death (1340 – 1771) – 200 million
  • Malaria (1600 – today): 100 million
  • AIDS (1981 – today): 25 million
  • Cholera (1817 – today): 100-500 thousand
  • Typhus (430 BC? – today): 10-30 million

About Pandemics

A pandemic occurs when a novel strain of a virus appears that causes readily transmissible human illness for which most of the population lacks immunity. Influenza pandemics, typically the most common, occur with little warning and hit wide geographic areas in multiple waves, lasting two to three months at a time. Health experts acknowledge that there is no way to determine if a variant strain of influenza or another disease altogether will cause the next pandemic.

The U.S. Federal Government estimates that as much as 40 percent of the nation’s workforce–including personnel supporting our critical communications infrastructure–will be absent during the height of a pandemic.[2]

How is a flu pandemic different from seasonal (regular) flu?

Both types of flu are caused by viruses that infect the nose, throat, and lungs. In the United States, flu season begins each year in the fall and can last as late as May. Every flu season, a vaccine is made to protect against seasonal flu.

A flu pandemic is caused by a new flu virus that spreads easily and makes many people sick around the world. For example, the 2009 H1N1 virus caused a flu pandemic. Unlike the seasonal flu, a flu pandemic is rare. Likewise, not all pandemics are the same. Pandemics can range from mild (similar to a regular flu season) to severe (with a lot of sickness and deaths).[3]



  1. CDC – Principles of Epidemiology in Public Health Practice – Lesson 1: Introduction to Epidemiology: http://www.cdc.gov/osels/scientific_edu/ss1978/lesson1/section11.html
  2. Federal Communications Commission (FCC) – Pandemics: http://transition.fcc.gov/pshs/emergency-information/pandemics.html
  3. Healthfinder.gov – Prepare for a Flu Pandemic: http://healthfinder.gov/HealthTopics/Category/everyday-healthy-living/safety/prepare-for-a-flu-pandemic
  4. Image Source: http://www.flu.gov/ [Accessed: February 22, 2014]