The term epidemic (from the Greek epi [on] plus demos [people]), first used by Homer, took its medical meaning when Hippocrates used it as the title of one of his famous treatises. At that time, epidemic was the name given to a collection of clinical syndromes, such as coughs or diarrheas, occurring and propagating in a given period at a given location. Over centuries, the form and meaning of the term have changed. Successive epidemics of plague in the Middle Ages contributed to the definition of an epidemic as the propagation of a single, well-defined disease. The meaning of the term continued to evolve in the 19th-century era of microbiology. Its most recent semantic evolution dates from the last quarter of the 20th century, and this evolution is likely to continue in the future.

At the start of the 21st century, epidemics of infectious diseases continue to be a threat to humanity. Severe acute respiratory syndrome, avian influenza, and HIV/AIDS have, in recent years, supported the reality of this threat. Civil wars and natural catastrophes are sometimes followed by epidemics. Climate change, tourism, the concentration of populations in refugee camps, the emergence of new human pathogens, and ecologic changes, which often accompany economic development, contribute to the emergence of infectious diseases and epidemics (1). Epidemics, however, have occurred throughout human history and have influenced that history. The term epidemic is [approximately equal to] 2,500 years old, but where does it come from?

Before Hippocrates

When works that put forward new ideas are translated, determining the original terminology (in Ancient Greek in this case) is not easy. In 430 BC, when Hippocrates was collecting the clinical observations he would publish in Epidemics, his treatise that forms the foundation of modern medicine, at least 3 terms were used in Ancient Greece to describe situations that resembled those described by Hippocrates: nosos, phtoros, and loimos (2).

Nosos, meaning disease, was used by Plato in the 4th century BC and clearly had the same meaning 2 centuries earlier in the works of Homer and Aeschylus. Nosos encompasses disease of the mind, body, and soul: physical, including epilepsy, and moral (i.e., psychological and psychiatric). Phtoros or phthoros means ruin, destruction, deterioration, damage, unhappiness, and loss, after war for example. The word was frequently used by Aeschylus and Aristophanes, was known in the 8th century BC, and was later used by Plato and Thucydides. Its meaning has remained general. Bailly translates loimos as plague or contagious scourge. Used by Esiodus in the 7th century BC and later by Sophocles and Herodotus, this term is ancient. Its translation as plague should be interpreted in the sense of a scourge rather than as the disease plague. In the Septuagint, a translation of the Old Testament into Greek by 70 Greek Jews from Alexandria, this word is used in the book of Kings to describe the 10 plagues of Egypt.

But the term epidemic already existed in 430 BC. The Greek word epidemios is constructed by combining the preposition epi (on) with the noun demos (people), but demos originally meant “the country” (inhabited by its people) before taking the connotation “the people” in classical Greek. Indeed, the word epidemios was used by Homer, 2 centuries before Hippocrates, in the Odyssey (canto I, verses 194 and 230), where it was used to mean “who is back home” and “who is in his country” in contrast to a voyager who is not: [TEXT NOT REPRODUCIBLE IN ASCII.], “because someone said that your father was back (home)” (canto I, verse 194). In this context, epidemios means indigenous or endemic. In the Iliad, Homer confirmed this meaning (canto XXIV, verse 262), by using also polemos epidemios to mean civil war:, “this one who [TEXT NOT REPRODUCIBLE IN ASCII.] liked passionately the frightening civil war” (canto IX, verse 64). Later, Plato and Xenophon (400 BC) used the word to describe a stay in a country or the arrival of a person: [TEXT NOT REPRODUCIBLE IN ASCII.], “a Parian who, I learned, was in town” (Plato, Apology, chapter I, paragraph 38). The verb epidemeo was used by Thucydides (460 BC-395 BC) to mean “to stay in one’s own country,” in contrast to apodemeo, “to be absent from one’s country, to travel.” For Plato, epidemeo meant “to return home after a voyage, to be in town.” Later, the orators Demosthenes (384 BC-322 BC) and Eschines (390 BC-314 BC) used this word to refer to a stranger who came to a town with the intention of living there, and the verb epidemeo was used to mean “to reside.” Typical of Greek semantics, epidemeo takes its meaning from the result of the action, rather than from the action itself. It relates to something that has already happened, with the implication that it had previously happened elsewhere. Authors before Hippocrates used epidemios for almost everything (persons, rain, rumors, war), except diseases. Hippocrates was the first to adapt this word as a medical term.