What is the Difference Between an Epidemic and a Pandemic?

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As new cases of the 2019 Novel Coronavirus (the disease this virus causes is known as COVID-19) are confirmed in an ever increasing number of countries, the words epidemic and pandemic being mentioned. The two words might seem interchangeable to some but they have two different meanings in terms of geography.

Difference Between Sporadic, Endemic, and Holoendmic Diseases

Diseases that occur infrequently or irregularly in a geographic area are called sporadic. When a disease is endemic, it means that it occurs persistently in a community. For example, malaria is an endemic disease to parts of Africa south of the Sahara, parts of India, and parts of Brazil. Holoendemic diseases are found in nearly everyone in a given population. Researchers found during their observations of a village in Senegal found that 98.6% of villagers contained trophozoites of P. falciparum at least once during a four-month study period (Trape et al., 1994).

This map shows an approximation of the parts of the world where malaria transmission occurs. Map: CDC

What is an Epidemic?

The word epidemic is formed from two Greek words, epi “upon or above” and demos “people”. Epidemics occur when a large number of people within a local population become infected over a short period of time. For an outbreak of a disease to be considered an epidemic, it has to surge above levels considered normal for the population at that time. The 2014–2016 outbreak in West Africa of the Ebola virus was an epidemic that was the largest occurrence of the disease since it was discovered in 1976. After starting Guinea it also affected neighboring Sierra Leone and Liberia.

Graph showing the progression of the Ebola epidemic in West Africa. Graph: Delphi234, CC0. Data source: WHO situation reports.

What is a Pandemic?

Pandemic stems from the Greek words pan “all” and  demos “people”. A pandemic is declared when a disease has spread and infected people across multiple continents or reached worldwide proportions. The most deadly pandemic was the 1918 influenza pandemic. 500 million people around the world were infected and at least 50 million people died. More recently, the 2009 H1N1 pandemic occurred. The novel coronavirus was first detected in 2009 in the United States, quickly spreading worldwide. It’s estimated that 151,700-575,400 people worldwide died from H1N1 during the first year.

References

Principles of Epidemiology: Home|Self-Study Course SS1978|CDC. (2019, March 7). https://www.cdc.gov/csels/dsepd/ss1978/index.html

Trape, J. F., Rogier, C., Konate, L., Diagne, N., Bouganali, H., Canque, B., … & Brahimi, K. (1994). The Dielmo project: a longitudinal study of natural malaria infection and the mechanisms of protective immunity in a community living in a holoendemic area of Senegal. The American journal of tropical medicine and hygiene51(2), 123-137.

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