index case

[in-deks keys]

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.

index case

noun

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

Word History and Origins

Origin of index case¹

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.

Read more on Los Angeles Times

Our investigations have not yet been able to identify the index case.

Read more on Scientific American

“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.

Read more on Seattle Times

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

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“Do you see transmission increasing in other parts of the world around presumed index cases?”

Read more on Science Magazine