The emergence of the novel coronavirus pandemic in 2020 has renewed global awareness of how rapidly infectious diseases can spread and impact life. However, the distinction between epidemics, pandemics and endemics is often blurred, even by medical experts, with each term used interchangeably for outbreaks of infectious disease that resemble one another. This article reveals what makes a disease an epidemic, how a pandemic differs from an epidemic and when a disease becomes endemic.
Epidemics are surges in cases of a particular disease that occur in a population above what would be expected on the basis of the disease’s natural history. In the early modern period, severe premodern pandemics such as smallpox and plague brought about significant social upheaval and weakened native peoples’ institutions and military capacity to the point of making them vulnerable to European conquest (Diamond 2009). The 3rd edition of the Oxford Companion to Medicine defines an epidemic as “the occurrence in a community or region of numbers of cases of disease clearly above normal expectations.” The definition does not include duration or infection but emphasizes the “above normal” rate of disease onset and spread.
The emergence of a pandemic requires rapid recognition by health care professionals and quick application of control measures. However, a lack of diagnostic capability at the local level increases the risk of an epidemic due to the delay in the ability to identify the pathogen and begin treatment. Local absorptive capacity—the ability to channel and effectively use external assistance during an outbreak—is also a factor that can limit the effectiveness of responses.