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The Plague of Athens (c. 1652 –1654) by Michiel Sweerts, illustrating the devastating epidemic that struck Athens in 430 BC, as described by the historian Thucydides. The United States Centers for Disease Control and Prevention defines epidemic broadly: "Epidemic refers to an increase, often sudden, in the number of cases of a disease above what is normally expected in that population in ...
The concept of waves in epidemics has implications especially for communicable diseases. A working definition for the term "epidemic wave" is based on two key features: 1) it comprises periods of upward or downward trends, and 2) these increases or decreases must be substantial and sustained over a period of time, in order to distinguish them ...
For a given epidemic or pandemic, the average of its estimated death toll range is used for ranking. If the death toll averages of two or more epidemics or pandemics are equal, then the smaller the range, the higher the rank. For the historical records of major changes in the world population, see world population. [3]
Epidemic A new disease that is spreading or a previously endemic disease whose infection rate is increasing significantly. [8] [11] Seasonal flu frequently appears as an epidemic. [8] Pandemic An epidemic affecting a very large part of the world, generally multiple countries or multiple continents. [8] Seasonal flu is sometimes a global ...
is the average number of people infected from one other person. For example, Ebola has an of two, so on average, a person who has Ebola will pass it on to two other people.. In epidemiology, the basic reproduction number, or basic reproductive number (sometimes called basic reproduction ratio or basic reproductive rate), denoted (pronounced R nought or R zero), [1] of an infection is the ...
An infectious disease is said to be endemic when it can be sustained in a population without the need for external inputs. This means that, on average, each infected person is infecting exactly one other person (any more and the number of people infected will grow sub-exponentially and there will be an epidemic, any less and the disease will ...
The number of cases varies according to the disease-causing agent, and the size and type of previous and existing exposure to the agent. Outbreaks include many epidemics, which term is normally only for infectious diseases, as well as diseases with an environmental origin, such as a water or foodborne disease. They may affect a region in a ...
[note 1] In the discussion of non-infectious diseases, a sporadic disease is a non-communicable disease (such as cancer) which occurs in people without any family history of that disease or without any inherited genetic predisposition for the disease (change in DNA which increases the risk of having that disease). [5]