Infective

Infective is an adjective used in medicine and microbiology to describe something capable of causing infection or relating to the capacity to establish infection. It can refer to an infectious agent, such as bacteria, viruses, fungi, or parasites, or to the stage of an infection during which a person can transmit the pathogen to others. The term is closely related to infectivity, which is the ability of a pathogen to establish infection in a host, and to infectious, which describes diseases that can be transmitted between hosts.

Infective dose refers to the minimum amount of an organism or its particles required to initiate infection in a susceptible host, while the infective period denotes the time during which an infected person can transmit the pathogen to others. These concepts help describe how easily a pathogen can start an infection and spread within a population.

The infectivity of a pathogen depends on multiple factors, including intrinsic properties of the organism (such as adherence to host cells, invasion, and replication), host factors (immune status, age, genetics), and environmental conditions (dose, route of exposure, and co-infections). Measuring infectivity involves laboratory assays and epidemiological studies; in population terms, the basic reproduction number, R0, reflects how infectivity combines with contact patterns and the duration of contagiousness to drive transmission.

Public health measures aim to reduce infectivity by interventions such as vaccination, antimicrobial or antiviral therapy, hygiene practices, and isolation or quarantine when warranted. In clinical and scientific usage, precise distinctions among infective, infectious, and infectivity help describe how diseases emerge, spread, and can be controlled. See also infectious disease, infectivity, and infectious dose.