index case

American  

[in-deks keys] / ˈɪn dɛks ˌkeɪs /

noun

Pathology.

1. the first documented instance of a disease or other medical condition in a population, especially the first infection in an epidemic.

2. (loosely) index patient.

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index case British  

noun

1. med the first case of a disease, or the primary case referred to in a report

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Etymology

Origin of index case

First recorded in 1935–40

Example Sentences

They include the likelihood that Ebola was spreading weeks before the index case was identified and that patients initially sought care at healthcare facilities with sub-optimal infection-control practices.

From Los Angeles Times • Oct. 17, 2022

“There is some evidence that passengers within two rows of an index case are at higher risk,” said Patricia Schlagenhauf, a professor of travel medicine at the University of Zurich.

From Seattle Times • Mar. 22, 2022

At least twice, those infections could have spread from an index case to other people, he says.

From Scientific American • Feb. 28, 2022

However guidance published by the WHO online appears to suggest that its goal is for 80% of the close contacts of each index case to be in quarantine within three days of them developing symptoms.

From BBC • Jul. 1, 2021

G. was the first identified case, the index case, in an outbreak of an unknown virus.

From "The Hot Zone" by Richard Preston