infectivity

{{Short description|Pathogen's ability to infect hosts}}

{{Distinguish|Injectivity}}In epidemiology, infectivity is the ability of a pathogen to establish an infection. More specifically, infectivity is the extent to which the pathogen can enter, survive, and multiply in a host. It is measured by the ratio of the number of people who become infected to the total number exposed to the pathogen.{{Cite book |title=Oxford textbook of global public health |date=2015 |publisher=Oxford university press |isbn=978-0-19-966175-6 |edition=6th |location=Oxford |pages=1486}}

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.{{cite journal | title=An empirical study of the evolution of virulence under both horizontal and vertical transmission | last1=Stewart | first1=AD | last2=Logsdon | first2=JM | last3=Kelley | first3=SE | journal=Evolution |date=April 2005 | volume=59 | issue=4 | pages=730–739 | doi=10.1554/03-330 | pmid=15926685| s2cid=924610 }}

A pathogen's infectivity is different from its transmissibility, which refers to a pathogen's capacity to pass from one organism to another.