What is a Pandemic?

The word pandemic comes to us from the Greeks. Pan- means "all" and demos means "the people," so a pandemic is an infectious disease outbreak with the potential to affect all people over a large geographic region, or even worldwide. In epidemiology, a pandemic is distinguished from an endemic (a stable but communicable disease like chickenpox in North America) and from an epidemic (an infectious disease spreading more than expected, but restricted to a smaller geographic region.)

Classification of a pandemic

The World Health Organization (WHO) uses a 6-phase pandemic classification index. Risk is low in phase 1 (animal infections only) and phase 2 (limited animal-to-human transmission) of an infectious disease outbreak. At phase 3 there may also be limited human-to-human transmission. Phase 4 sees human-to-human transmission in a "community-level outbreak." Phase 5 sees the disease spread to at least two countries within a single WHO administrative region. Only at phase 6, which involves spread to a second geographic region, is a pandemic officially declared.

A misunderstanding of what constitutes a pandemic has led to criticism over how the WHO handled the 2009 H1N1 global pandemic. The American Centers for Disease Control and Prevention (CDC) have developed a 5-category Pandemic Severity Index (PSI) that responds to the public's desire for information on severity of individual cases of a disease. All infectious disease outbreaks measured on the PSI are pandemics, however the scale puts into perspective the destructive potential of a disease. It allows comparison of a new pandemic, like the 2009 swine flu, with past ones such as the much more deadly 1918 Spanish flu.

Historical pandemics

The Plague of Athens of 430 BCE is probably the first recorded human pandemic. Thucydides describes the outbreak, which affected Ethiopia and other parts of the Mediterranean: "people in good health were all of a sudden attacked by violent heats in the head, and redness and inflammation in the eyes, the inward parts, such as the throat or tongue, becoming bloody and emitting an unnatural and fetid breath." Up to one-third of the population died. The pandemic had an immediate effect on law and order in Athens, and the older generation who served as the leaders in Athens were not replaced until some time afterwards.

The Black Death travelled from China to Europe around 1347. Over a period of five years, bubonic plague wiped out some 25 million people. There were labour shortages all over Europe, but landlords refused to pay higher wages for capable workers. Physicians who had been helpless to cure the sick questioned their training. They began to study anatomy, and to develop new approaches to the treatment of illness. The 14th century pandemic of bubonic plague ultimately contributed to revolutions in England, France, Belgium and Italy. It also made the way clear for the coming of the Renaissance.

Smallpox developed as a result of close human contact with a variety of domesticated cattle. Over thousands of years of farming the disease mutated, becoming deadly. Outbreaks in heavily populated areas resulted in numerous deaths, but some people developed immunity and passed it on. Smallpox came to the New World with European colonists in the 16th century. A pandemic devastated native peoples in both North and South America, who had never been exposed to anything like it. Infectious diseases like smallpox, measles and influenza had a greater negative impact on the indigenous peoples of the Americas, than any weapon of the colonists.

Pandemics today

Infectious diseases like smallpox, measles and even bubonic plague still exist today, though they are only rarely seen in the western world. We can prevent many with vaccination, and antibiotics make it possible to treat those who become ill. Global outbreaks of infectious disease do still occur, however. The 2009 H1N1 influenza pandemic and the HIV/AIDS pandemic that has ravaged Africa and affected people on every populated continent, are a reminder that we are vulnerable. Understanding preventative measures goes a long way towards decreasing both fear and transmission rates.

Sources:

"The Black Death: Bubonic plague." MiddleAges.net

"Early discoveries." Science Clarified

"Pandemic Severity Index." CDC

"The Plague in Athens during the Peloponnesian War." The Asclepion (Indiana University)

"The story of . . . Smallpox - and other deadly Eurasian germs." Guns, Gems and Steel (PBS)

Thucydides, "History of the Peloponnesian War," Second Book. Internet Classics Archive

"WHO pandemic phase descriptions and main actions by phase." World Health Organization