infectivity

noun

in·​fec·​tiv·​i·​ty (ˌ)in-ˌfek-ˈti-və-tē 

plural infectivities

: the ability to produce or transmit infection : the quality or state of being infective

The onset of cough on the second day of illness in this patient, followed by clinical evidence of pneumonia four days later, raised the question of his infectivity during the four days before hospitalization.

—B. Johnson et al.

Even when there are apparently high levels of the virus in the blood, there may be much less infectivity. … a thousand or more of these particles are needed to produce infection.

—Charles Marwick

specifically : the capacity to spread from host to host

The swine flu's infectivity is rated at about 2.5, meaning that every infected person can spread the infection to 2.5 people and it doesn't take a math major to understand that implication.

—Dennis Bloomfield

Examples of infectivity in a Sentence

Recent Examples on the Web

Two mutations in particular gave the virus a slight edge in infectivity and antibody evasion. —Sarah Zhang, The Atlantic, 24 Feb. 2025

Furthermore, when the infectivity of these viruses was evaluated in cultured cells, KP.3 needed a lower amount of virus to cause an infection compared to LB.1 and KP.2.3, which both required roughly the same amount of virus as JN.1. —Ritsuko Kawai, WIRED, 24 July 2024

Key Takeaways Infectious disease experts say that COVID-19’s peak infectivity is during symptom onset. —Nick Blackmer, Verywell Health, 11 Dec. 2023

However, the infectivity of BA.2.86 may be much lower than XBB.1.5 and EG.5. —Byerin Prater, Fortune Well, 1 Sep. 2023

Word History

Etymology

infective + -ity

First Known Use

1871, in the meaning defined above

Rhymes for infectivity

• absorptivity
• affectivity
• collectivity
• conductivity
• connectivity
• corrosivity
• creativity
• diffusivity
• directivity
• effectivity
• emissivity
• exclusivity

Medical Definition

infectivity

noun

in·​fec·​tiv·​i·​ty ˌin-ˌfek-ˈtiv-ət-ē 

plural infectivities

: the quality of being infective : the ability to produce or transmit infection

When sporozoites are incubated with serum from the protected animals, their infectivity is neutralized and prominent deposits of antibody appear over the surface of the parasite …

—Louis H. Miller et al., Science

The onset of cough on the second day of illness in this patient, followed by clinical evidence of pneumonia four days later, raised the question of his infectivity during the four days before hospitalization.

—B. Johnson et al., The Journal of the American Medical Association

specifically : the capacity to spread from host to host

The swine flu's infectivity is rated at about 2.5, meaning that every infected person can spread the infection to 2.5 people and it doesn't take a math major to understand that implication.

—Dennis Bloomfield, Staten Island (New York) Advance