Pandemic: Epidemic of infectious disease that has spread across a large region with global health impact

According to the World Health Organization, a pandemic exists when three conditions have been met:

• A disease emerges that is new to a population.
• The agent that causes the disease infects humans, causing serious illness.
• The agent spreads easily and sustainably among humans.

A disease or condition is not a pandemic merely because it is widespread or kills many people. It must also be infectious. For example, cancer causes many deaths, but it is not a pandemic because it is usually not infectious.

The World Health Organization (WHO) has developed a plan to prepare the global fight against influenza. It defines the stages of a pandemic and makes recommendations about what countries should do before and during a pandemic. The phases are:

Interpandemic period:

• Phase 1: No new influenza virus subtypes have been detected in humans.
• Phase 2: No new influenza virus subtypes have been detected in humans. However, a variant of the virus causes disease in animals. This means there is a threat of human disease.

Pandemic alert period:

• Phase 3: Humans get infected with a new subtype of the flu virus. However, the virus is not spreading from person to person.
• Phase 4: There are small cluster(s) of flu infection. Person-to-person spread is limited and localized.
• Phase 5: There are larger cluster(s) of flu infection. Person-to-person spread is still localized.

Pandemic period:

• Phase 6: Pandemic: The flu has spread throughout the general population. Person-to-person spread is increased and sustained..

• Epidemic
• List of epidemics

• Steward's "The Next Global Threat: Pandemic Influenza".

• WHO - Authoritative source of information about global health issues
• Past pandemics that ravaged Europe
• CDC: Influenza Pandemic Phases
• U.S. government's pandemic flu and avian flu information site