Endemic – Pandemic

Endemic, Epidemic, Epizootic, Pandemic. These terms define the frequencies with which diseases occur within a population, in a certain amount of time.

Endemic describes the frequency of a disease where percentage of people infected in a population constantly remains the same. This means that on average, one person infects exactly one other person. The percentage of persons infected within the population doesn’t change. The basic reproduction number of the disease equals one. Examples of endemics are Chickenpox in European or Malaria in African countries.

The word endemic derives from Greek “en” meaning “within” and “demos” meaning “people”.

If the infection rate increases the endemic switches to an epidemic state, for example, with AIDS in African countries. An epidemic defines the outbreak of a disease in proportions that exceed the rates that are normal or expected. An epidemic will at some point either die out, or decrease, at some point it may break out again, or reach an endemic state.

The word epidemic derives from Greek “epi” meaning “upon”. An epidemic becomes a pandemic when a disease spreads over different continents or even worldwide. “Pan” means “all”.

If a disease spreads only among animals it is named “epizootic”.