index patient

American  

[in-deks pey-shuhnt] / ˈɪn dɛks ˌpeɪ ʃənt /

noun

Pathology.

1. the first person known to have a particular disease or other medical condition in a population, especially the first patient in an epidemic known to have contracted the infection.

   The index patient did not immediately test positive, and consequently spread the virus for several days.

---

Etymology

Origin of index patient

First recorded in 1950–55

Example Sentences

The Portuguese researchers sequenced the virus from a sample collected on 4 May, which means the infected person likely had no connection to the index patient in the United Kingdom.

From Science Magazine • May 20, 2022

Investigators suspected cases were driven in part by the apartment’s sanitary system, because the outbreak seemed to begin after an index patient suffering from diarrhea used a toilet in the apartment complex.

From Washington Post • Jun. 16, 2020

That man became Nigeria's first Ebola case—the index patient.

From Scientific American • Oct. 18, 2014

The virus spread from that one index patient to 318 people, resulting in 280 deaths.

From Nature • Oct. 8, 2014

Without knowing the index patient, investigators can’t know how the fateful spillover happened.

From New York Times • Apr. 9, 2014