A epidemic indicates the appearance, the development or the fast propagation of a Infectious illness with the significant effects, generally by Contagion, increasing the incidence disease within a population compared to the normal.
A Endémie, which is the usual presence of a disease in an geographical area (positive Prévalence, stable incidence) can develop in epidemic if the environmental conditions allow it. Thereafter an epidemic always evolves/moves in Pandémie or regresses (the incidence becoming very low, zero or negative) in endémie, the disease possibly being able to disappear at the end.
An epidemic can also emerge without there being preliminary endémie, for example following an accident causing the dissemination of the pathogenic vector in an environment where it was hitherto non-existent (Prévalence and initially null incidence). In such circumstances, only some cases are enough to cause a very significant increase in incidence in the disease and to give him the character of epidemic.
Etymology, and extension of the initial directionAlthough by its Greek etymology ( Demonstrations meaning people), this word initially applies to the diseases concerning the human , it is frequently used in the current language to speak about the diseases touching of the groups of animals (Zoonose S).
Indeed, the adapted term, epizooty, are less known, and it is frequent that identical medical phenomena in the animal and the human one are indicated by the same words in the current language.
The use of the term in the current language also tends to be unaware of or confuse the incidence and the Prévalence of the disease. Thus for example the qualifier of epidemic is often restricted wrongly with the only circumstances where the prevalence is important, when there is many sick individuals without taking account of their initial number, and thus being unaware of the normal incidence.
BehaviorThe epidemics are often cyclic; the Grippe is a perfect example of cyclic epidemic, with a cycle known as annual or " seasonal ".
The epidemics can occur in one or more waves, as it was the case with the Spanish Grippe in 1918-1919.
The term is also used, for example by the the World Health Organization (WHO) for other phenomena that infectious illness, for example for the fast development of the Obésité on planet.
The follow-up of the epidemicsThe epidemic can remain localized in space and become endemic with certain areas (current case of the Polio), or extend and become a Pandémie (case of HIV).
Currently, a epidemiologic Veille is maintained by networks general doctors or hospital, pharmacists and/or cities known as sentinel , on the basis of standardized protocol, with the local scales, regional, national and continental, even world in the case of diseases such as the influenza.
The experts estimate that the emergent diseases, in particular of animal origin, will take an increasing importance, with the population growth, urban promiscuity, the climatic modifications, the increase in displacements of goods and people the increase in the mutagen factors, and the contact with new microbes.
Epidemiologic thresholdA epidemiologic Seuil, corresponding to a minimal number of patient at the moment T is defined for the great diseases, in order to be able to compare the epidemiologic evolutions between cities, areas, country or continents, at various times.
Under this threshold, one does not speak about epidemic. With the top, preventive measures and precaution can be decided or solicited by the health authorities. The number of the patients in time generally describes a bell-shaped curve.
The epidemic corresponds to the increase or of an endemic disease or to the appearance of a great number of patients where the disease was absent. It can also translate the description of the change of pathogenic which makes visible by the gravity of the symptoms a disease which was asymptomatic before.
ModelingOne seeks to anticipate the epidemics for better countering them. For that the researchers try to develop and validate mathematical models.
This work is made difficult by the capacity of certain pathogenic with quickly transferring (Virus with ARN, of which the Grippe for example) by quickly changing their characteristic (of which contagiousness, virulence…).
It seems that conurbations and their promiscuity modify the ecology of unquestionable pathogenic while enabling them to be active all the year, although in a discrete way (one speaks then sometimes about “ background noise ”).
- DGS-urgent, mailing list of the Head office of health (ministry for Health, France)
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