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Public Health & Epidemiology vocabulary · Outbreaks and Transmission

Index case

Meaning in public health & epidemiology, with examples

nounCommon term

In public health & epidemiology, index case means: The first case of a disease that comes to the attention of health authorities in an outbreak or a family, leading investigators to look for others.

In Turkish: indeks olgu, ilk saptanan olgu

How it is used

Investigators interview the index case to find contacts and the likely source. The index case is not always the first person infected; that person is called the primary case. The media often use the phrase 'patient zero'.

Example sentences

  1. The index case was a nurse who had returned from a conference abroad.

  2. All household contacts of the index case were tested.

Common collocations

  • identify the index case
  • primary case
  • patient zero
  • contacts of the index case
  • caseA person in a population or study who has the disease, infection or condition being investigated, usually decided by agreed criteria.
  • contact tracingFinding and contacting people who have been near an infected person, so they can be informed, tested, watched for symptoms or asked to stay at home.
  • outbreakA sudden rise in the number of cases of a disease above what is normally expected, usually limited to one place, group or event.
  • clusterA group of cases that occur closer together in time or place than would be expected, which may or may not turn out to share a common cause.

More terms: Outbreaks and Transmission

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This page explains English vocabulary for learners. It is not medical advice.