Definition

Noun: 1. The initial documented case in an outbreak: The first known or identified case of a disease in a specific outbreak or epidemiological study. This case serves as a reference point for investigating the origin and spread of the disease.

Usage

The term "index case" is used in epidemiology and public health to identify the starting point of an investigation. It is a formal, technical term. * It is often used with verbs like identify, locate, trace, or investigate. * It is typically followed by of to specify the disease (e.g., index case of measles).

Examples

• Health officials worked tirelessly to identify the index case in the recent salmonella outbreak.
• The index case was a traveler who returned from the affected region two weeks ago.
• All subsequent infections were traced back to the index case.

Advanced Usage

• Synonyms: , (Note: "patient zero" is a more popular, sometimes sensationalized term, while "index case" is the standard scientific term).
• The identification of the index case is crucial for understanding transmission chains and implementing effective containment measures.

Variants and Related Words

• Index patient: A synonymous term, emphasizing the person rather than the abstract "case."
• Primary case: Often used interchangeably with "index case," though some definitions distinguish it as the first case that brings the outbreak to the attention of authorities.

Synonyms

• Primary case
• Patient zero (colloquial/media term)

Notes

• The index case is not necessarily the person who first contracted the disease, but the first case in the study or investigation.
• It is a key concept for contact tracing, where health workers identify and monitor people who may have been exposed to the disease starting from the index case.

Noun

1. the earliest documented case of a disease that is included in an epidemiological study