Epidemic and pandemic: what's the difference

A. An epidemic - from the Greek epidemos, 'to the people' - refers in its strictest sense to an infectious disease affecting a disproportionately large number of individuals within a population or region at the same time. In recent decades the definition of an epidemic has been extended to include outbreaks of any chronic disease influenced by the environment, such as heart disease and cancer. A pandemic - from pandemos, 'all of the people' - is an outbreak of a disease over a wide geographical area and affecting an exceptionally high proportion of the population, so it can be said to be 'widely epidemic'. No figure has been set at which an illness officially become an epidemic in terms of percentage of the population.

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Q. So, is the foot and mouth outbreak currently raging throughout the UK an epidemic or a pandemic
A. Technically neither: pedants would suggest that it is epizootic, that is 'to animals'. However, not to make light of a dire situation, it is really an epidemic, as the pockets of infection are dotted around the country and do not comprise significantly large numbers of animals.

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Q. What examples are there of pandemics
A. HIV/AIDS can be said to be pandemic as it is infectious and affects populations throughout the world in very large numbers. Malaria is another, although a distinction can be made here in that malaria is endemic, that is prevalent over long periods of time in fixed geographical area. Endemic diseases can become classed as epidemic during periods of high prevalence. A number of pandemics struck human populations in the last millennium:

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The Black Death - probably a combination of bubonic and pneumonic plagues - which ravaged Europe between 1347 and 1351 is estimated to have killed one-third of the population of Europe, some 25 million, and numbers did not reach mid 14th-century levels again for 200 years. Some countries suffered more than others. In England, for example, a truer mortality rate may have been as much as 50%. A pandemic even more dramatic in terms of the proportion of a population killed took place in Mexico throughout the 16th century, when 90 per cent of the native population died through successive waves of smallpox and measles brought in by Europeans. Most recently, in 1918-19, the Spanish flu, a particularly virulent strain, killed an estimated 30 million people worldwide, 12.5 million in India alone.

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Q. What else does epidemic mean
A. It can be used in an extended sense to refer to the spread or prevalence of anything from nose-rings to TV makeover programmes. It also can be applied to the sudden growth of a population, particularly of vermin.

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By Simon Smith