What does infectiousness mean?
Infectiousness is the quality of being capable of spreading an infection from one person or organism to another. It is especially important in epidemiology, where researchers assess how readily a pathogen can be transmitted and how that transmission may be controlled. The degree of infectiousness can vary within a disease, among individual cases, and between strains of the same organism, so medical guidance may change as evidence accumulates. Although related to terms such as infectivity and transmissibility, infectiousness is also used more generally for qualities that spread readily, including laughter, enthusiasm, or excitement. It should not be confused with virulence, which describes how severe or damaging a disease is, or pathogenicity, which denotes an organism's ability to cause disease. Understanding infectiousness is crucial for estimating exposure risk, designing preventive measures, and understanding the social behavior of outbreaks.
nounThe quality or degree of being infectious, especially the capacity of a disease, pathogen, or person to transmit infection to others.
- The quality or degree of being infectious, especially the capacity to transmit an infection.
"Public-health officials studied the infectiousness of the virus before introducing the new control measures."
"The infectiousness of the disease varies considerably among patients."
"Researchers used laboratory data to estimate the infectiousness of the new strain."
The plural is grammatically correct but rarely needed in ordinary usage.
"The study compared the infectiousnesses of several viral strains."
Two infections can be equally harmful yet very different: one spreads easily, while the other is exceptionally difficult to pass on.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does infectiousness come from?
Infectiousness derives from the adjective infectious, which comes from infection. Infection ultimately derives from Latin inficere, meaning "to put into" or "to taint." The same Latin root also underlies infective, which describes something that can produce infection.
How infectiousness is actually used
This is primarily a formal or scientific term used in medicine, epidemiology, and public health. In everyday discussion, terms such as "contagiousness" may sound more natural.
Easily confused with infectiousness
Infectiousness concerns how readily an infection is transmitted, whereas virulence concerns the severity of the disease or harm it causes.
Infectiousness measures transmissibility, while pathogenicity refers to an organism's ability to cause disease in a host.