What Is A Pandemic? What Is An Epidemic?

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Main Category: Infectious Diseases / Bacteria / Viruses
Also Included In: Swine Flu;  Public Health;  Flu / Cold / SARS
Article Date: 05 May 2009 - 10:00 PDT

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The word pandemic comes from the Greek pandemos meaning "pertaining to all people". The Greek word pan means "all" and the Greek word demos means "people". According to the Medilexicon´s medical dictionary a pandemic is "Denoting a disease affecting or attacking the population of an extensive region, country, continent, global; extensively epidemic."

A pandemic is an outbreak of global proportions. It happens when a novel virus emerges among humans - it causes serious illness and is easily human transmissible (spreads easily from person-to-person).

What is the difference between a pandemic and an epidemic?

A pandemic is different from an epidemic or seasonal outbreak.

• Put simply, a pandemic covers a much wider geographical area, often worldwide. A pandemic also infects many more people than an epidemic. An epidemic is specific to one city, region or country, while a pandemic goes much further than national borders.


• An epidemic is when the number of people who become infected rises well beyond what is expected within a country or a part of a country. When the infection takes place in several countries at the same time it then starts turning into a pandemic.


• A pandemic is usually caused by a new virus strain or subtype - a virus humans either have no immunity against, or very little immunity. If immunity is low or non-existent the virus is much more likely to spread around the world if it becomes easily human transmissible.


• In the case of influenza, seasonal outbreaks (epidemics) are generally caused by subtypes of a virus that is already circulating among people. Pandemics, on the other hand, are generally caused by novel subtypes - these subtypes have not circulated among people before. Pandemics can also be caused by viruses, in the case of influenza, that perhaps have not circulated among people for a very long time.


• Pandemics generally cause much higher numbers of deaths than epidemics. The social disruption, economic loss, and general hardship caused by a pandemic are much higher than what an epidemic can cause.

How do influenza pandemics emerge?

A pandemic can emerge when the influenza A virus changes suddenly - what experts call an antigenic shift. The HA and/or NA proteins, which are on the surface of the virus, have new combinations; resulting in a new influenza A virus subtype.

This new influenza subtype needs one characteristic to cause a pandemic - it must be easily human transmissible (it can easily spread from one person to another).

After the pandemic has emerged and spread, the virus subtype circulates among humans for several years, causing occasional flu epidemics. These will not usually become more than epidemics because humans have developed some immunity over time. Various bodies around the world, such as the Health Protection Agency (UK), the World Health Organization (WHO), and the Centers for Disease Control and Prevention (USA) monitor the behavior and movements of the virus.

Examples of pandemics throughout history

Below you can see the dates of the most famous pandemics throughout history. Some may have been epidemics which crossed borders but did not go right round the world:

• Antonine Plague (possibly smallpox) 165-180 A.D.
• Plague of Cyprian 251-266 A.D.
• Plague of Justinian 541 A.D.
• Black Death 1300s A.D.
• Typhus 1501-1587 A.D.
• Influenza 1732-1733 A.D.
• Influenza 1775-1776 A.D.
• Cholera 1816-1826 A.D.
• Cholera 1829-1851 A.D.
• Influenza 1847-1848 A.D.
• Cholera 1852-1860 A.D.
• Bubonic Plague 1855 A.D.
• Influenza 1857-1859 A.D.
• Cholera 1863-1875 A.D.
• Influenza 1889-1892 A.D.
• Cholera 1899-1923 A.D.
• Spanish Flu (avian flu) 1918-1920 A.D.
• El Tor (Vibrio cholerae - cholera) 1960s A.D.
• HIV/AIDS 1980s-to date
• Swine Influenza - 2009 (experts say not likely to cause many deaths)

What are the Six Stages of a pandemic?

The World Health Organization has a Six Stage influenza program, plus two Periods:

• Stage 1
  No animal influenza virus circulating among animals have been reported to cause infection in humans.


• Stage 2
  An animal influenza virus circulating in domesticated or wild animals is known to have caused infection in humans and is therefore considered a specific potential pandemic threat.


• Stage 3
  An animal or human-animal influenza reassortant virus has caused sporadic cases or small clusters of disease in people, but has not resulted in human-to-human transmission sufficient to sustain community-level outbreaks.


• Stage 4
  Human-to-human transmission of an animal or human-animal influenza reassortant virus able to sustain community-level outbreaks has been verified.


• Stage 5
  The same identified virus has caused sustained community level outbreaks in two or more countries in one WHO region.


• Phase 6
  In addition to the criteria defined in Phase 5, the same virus has caused sustained community level outbreaks in at least one other country in another WHO region.


• LOST PEAK PERIOD
  Levels of pandemic influenza in most countries with adequate surveillance have dropped below peak levels.


• POST PANDEMIC PERIOD
  Levels of influenza activity have returned to the levels seen for seasonal influenza in most countries with adequate surveillance.

According to the WHO, if an influenza pandemic were to emerge today, we could expect:

• As people today are highly internationally mobile, the pandemic virus would spread rapidly around the world.


• Vaccines, antiviral agents, and antibiotics to treat secondary infections would rapidly be in short supply


• Several months would be needed before any vaccine became available. This is because pandemic viruses are new ones.


• Medical facilities would be overwhelmed


• There would be sudden and potentially considerable shortages of personnel to provide vital community services as the illness became widespread.

Interesting links

• See our Map Of H1N1 Outbreaks
• See our Mexico Swine Flu Blog

Written by Christian Nordqvist
Copyright: Medical News Today
Not to be reproduced without permission of Medical News Today

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