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Transmission of infection by direct contact. In common usage and in public health, “contagious” implies a condition that is highly infectious and usually severe, although one of the most contagious diseases, the common cold, is seldom severe. “Contagion” can be stigmatizing when it is emotionally associated with a distasteful disease, such as leprosy, or with what used to be called venereal diseases, so “contagion” can imply a condition that is unclean or immoral. In De Contagione (1546) Girolamo Fracastorius (1484–1553) identified three modes of contagion: direct contact, droplet spread, and via contaminated clothing, domestic utensils, etc. Other modes of spread are by common vehicle spread in infected or contaminated water, food, or air, and vector-borne transmission, but the etymology of contagion, from the Latin con (together) tangere (to touch) implies intimate contact, so purists prefer to restrict use of the word to communicable diseases transmitted by direct person-to-person contact.

Subjects: Public Health and Epidemiology.

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