What is the capacity of an infectious agent to cause disease known as?

The capacity of an infectious agent to cause disease is referred to as virulence. Virulence is a measure of the severity of the disease that can be caused by an infectious organism. It encompasses factors such as the agent's ability to invade host tissues, evade the immune response, and produce toxins.

Understanding virulence is essential in the field of infection control because it helps healthcare providers assess the potential risk associated with different pathogens. For instance, highly virulent organisms can lead to more severe disease outcomes even in a small number of invading organisms, while those with lower virulence may require a larger number of organisms to produce disease.

Infectivity pertains to an organism's ability to enter, survive, and multiply in a host, but it does not specifically relate to disease severity. Pathogenicity refers to an organism’s ability to cause disease in general but does not capture the degree of severity involved. Inoculum potential refers to the quantity of an infectious agent required to initiate an infection, which is also distinct from virulence. Thus, virulence uniquely identifies the potential impact of the infectious agent on the host when disease occurs.