Asymptomatic infection

An infection in which the infected person develops no noticeable signs or symptoms. The infection may still be detectable and transmissible.

Pathogen: A biological agent that causes disease in a host. Pathogen traits influence whether an infection causes noticeable illness.
Symptomatic infection: An infection that produces noticeable signs or symptoms. It is the direct clinical opposite of asymptomatic infection.
Transmission: The spread of an infectious agent between hosts or through the environment. Asymptomatic infection matters because spread can occur without obvious illness.
Presymptomatic transmission: Transmission of an infectious agent by a person before that person develops symptoms. It separates transmission before illness from transmission during an entirely symptom-free infection.
Asymptomatic fraction: The proportion of infections that produce no noticeable symptoms throughout their course. Estimating this fraction requires distinguishing lasting silence from symptoms that appear later.
Host–pathogen interaction: The dynamic relationship between an infectious agent and the organism it infects. The balance between pathogen activity and host response shapes symptoms.
Presymptomatic infection: An infection detected before symptoms begin in someone who later develops them. It is temporary silence before illness, not absence of symptoms throughout infection.
Contact tracing: The process of identifying and notifying people exposed to an infectious case. Tracing can find infections that symptom-based case detection misses.
Infection fatality rate: The proportion of all infected people who die from an infection, including undiagnosed cases. Uncounted asymptomatic infections can enlarge the denominator and alter risk estimates.
Symptom ascertainment: The process of determining whether and when symptoms occur in a person or study population. Mild or unreported symptoms can cause infections to be misclassified as asymptomatic.

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