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In epidemiology, infectivity is the ability of a pathogen to establish an infection. More specifically, infectivity is a pathogen's capacity for horizontal transmission — that is, how frequently it spreads among hosts that are not in a parent–child relationship. The measure of infectivity in a population is called incidence.[citation needed]

Infectivity has been shown to positively correlate with virulence, in plants. This means that as a pathogen's ability to infect a greater number of hosts increases, so does the level of harm it brings to the host.[1]

A pathogen's infectivity is subtly but importantly different from its transmissibility, which refers to a pathogen's capacity to pass from one organism to another.[citation needed]

See also[edit]


  1. ^ Stewart, AD; Logsdon, JM; Kelley, SE (April 2005). "An empirical study of the evolution of virulence under both horizontal and vertical transmission". Evolution. 59 (4): 730–739. doi:10.1554/03-330. PMID 15926685.