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.
[1] 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.
This infectious disease article is a stub.