Epidemic

An epidemic is the occurrence of a disease or health condition in a population at a level higher than expected in a particular place and period.

Basic reproduction number: The average number of secondary infections caused by one infected person in a fully susceptible population. It estimates whether an epidemic can grow when a pathogen enters a susceptible population.
Endemic: The usual, sustained presence of a disease within a population or geographic area. An epidemic exceeds the expected level; endemic disease persists at its customary level.
Epidemic curve: A graph of new disease cases over time during an outbreak or epidemic. Its shape can reveal an epidemic’s timing, pace, and possible transmission pattern.
Black Death: The devastating pandemic of plague that spread through Europe, Asia, and North Africa in the fourteenth century. Its immense mortality shows how epidemic spread can reshape societies.
Incubation period: The time between infection and the onset of symptoms. It shapes how long infected people may transmit disease before recognizing illness.
Outbreak: A localized increase in disease cases above what is normally expected. The term often describes a limited epidemic, especially in a defined setting.
Case fatality rate: The proportion of diagnosed cases of a disease that result in death. It helps characterize severity, though changing case detection can distort comparisons.
1918 influenza pandemic: A global influenza pandemic caused by an H1N1 virus that killed tens of millions of people. Its rapid worldwide spread illustrates epidemic dynamics before modern vaccines and antiviral drugs.
Generation time: The interval between infection in a primary case and infection in a secondary case. It helps determine how quickly successive waves of transmission unfold.
Pandemic: An epidemic that spreads across multiple countries or continents and affects many people. A pandemic is an epidemic with exceptionally broad geographic spread.

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