A Pandemic is is an epidemic of infectious disease that spreads through populations across a large region; for instance a continent, or even worldwide.
It is used as a technical term, and so should not cause panic when health orgnaisations and officials refer to swine flu as a potential pandemic.
Practical definitions of a pandemic vary. "Pan" suggests everywhere, but the World Health Organization (WHO) Level 6 requirement for a pandemic indicates that there are serious outbreaks in communities two or more different WHO regions.
According to the WHO, a pandemic can start when three conditions have been met:
- Emergence of a disease new to a population.
- Agents infect humans, causing serious illness.
- Agents spread 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 instance, cancer is responsible for many deaths but is not considered a pandemic, because the disease is not infectious or contagious.