Is 'index case' the same as 'patient zero'?

Not exactly. 'Index case' is the technical term for the first case identified by health authorities. 'Patient zero' is a more informal, often media-driven term that can imply the absolute origin of an outbreak, which is harder to prove.

Can 'index case' be used outside of medicine?

It is highly specialised. While it can be used metaphorically (e.g., 'the index case of a social trend'), this is rare and likely to be understood only by analogy to its medical meaning.

What is the verb form related to 'index case'?

To 'index' (a case/disease). It means to record, catalog, or designate something systematically, often as part of an investigation.

How do you find the index case?

Through epidemiological detective work: interviewing patients, tracing their contacts, and using laboratory data (like genetic sequencing of the pathogen) to build a transmission chain back to the earliest known case.

index case

Low

UK/ˈɪndɛks keɪs/US/ˈɪndɛks keɪs/

Technical/Academic

My Flashcards

Definition

Meaning

The first documented case of a disease in a population or outbreak, which serves as the point of origin for epidemiological investigation.

By extension, the first identified instance of any phenomenon in a series, serving as a reference point for further study or comparison.

Linguistics

Semantic Notes

Used almost exclusively in epidemiology, public health, and related scientific fields. It is a technical term, not a general medical term for 'first patient'. It specifically refers to the case that leads to the identification and investigation of an outbreak.

Dialectal Variation

British vs American Usage

Differences

No significant differences in meaning or usage. Spelling follows local conventions ('-ise' vs '-ize' in related verbs like 'indexing').

Connotations

Identical technical and neutral connotations in both varieties.

Frequency

Equal frequency in medical and public health discourse in both regions.

Vocabulary

Collocations

strong

identify the index casetrace back to the index casethe original index caseconfirmed index casesuspected index case

medium

locate the index caseinterview the index casetreat the index caseisolate the index caseoutbreak's index case

weak

investigate the index casecluster's index casefamily index casecommunity index caseprimary index case

Grammar

Valency Patterns

The index case of [disease/outbreak]identified [someone] as the index caseserve as the index case for

Vocabulary

Synonyms

Strong

patient zeroproband (in genetics)

Neutral

primary caseinitial casefirst identified case

Weak

source casestarter case

Vocabulary

Antonyms

secondary casetertiary caselast casefinal case

Phrases

Idioms & Phrases

“[none specific to this term]”

Usage

Context Usage

Business

Extremely rare. Might be used metaphorically in business analysis to mean the first instance of a trend or problem.

Academic

Core term in epidemiology, public health, and medical research papers.

Everyday

Very rare. Might appear in news reports during major disease outbreaks.

Technical

Essential term in disease surveillance, outbreak investigation, and contact tracing protocols.

Examples

By Part of Speech

verb

British English

Health officials worked to index all cases related to the outbreak.

American English

The team needs to index the cases chronologically to find the source.

adverb

British English

[No standard adverbial use]

American English

[No standard adverbial use]

adjective

British English

The index-case patient has been isolated.

American English

The index-case identification is our top priority.

Examples

By CEFR Level

The doctor found the first sick person. This person is called the index case.

Scientists identified the index case as a traveller who returned from abroad.

Contact tracing began immediately after the index case was confirmed, in an effort to contain the spread.

Genomic sequencing revealed that the index case was part of a larger, previously undetected transmission cluster.

Learning

Memory Aids

Mnemonic

Think of the index at the back of a book: it's the starting point to find information. The 'index case' is the starting point to find the source of an outbreak.

Conceptual Metaphor

ORIGIN AS SOURCE/PATH: The index case is conceptualised as the source from which a path of infection flows.

Watch out

Common Pitfalls

Translation Traps (for Russian speakers)

Avoid direct calque 'индексный случай' as it is not standard. Use 'первичный случай' or 'случай-источник'.
Do not confuse with 'patient zero' (нулевой пациент), which is a more media-driven term; 'index case' is more technical.

Common Mistakes

Using 'index case' to mean any important or severe case.
Confusing it with 'case study' in non-epidemiological contexts.
Incorrectly pluralising as 'indexes case' instead of 'index cases'.

Practice

Quiz

Fill in the gap

Epidemiologists worked backwards from the latest infections to try and identify the .

Multiple Choice

In an epidemiological context, what is an 'index case'?

FAQ

Frequently Asked Questions

: Not exactly. 'Index case' is the technical term for the first case identified by health authorities. 'Patient zero' is a more informal, often media-driven term that can imply the absolute origin of an outbreak, which is harder to prove.
: It is highly specialised. While it can be used metaphorically (e.g., 'the index case of a social trend'), this is rare and likely to be understood only by analogy to its medical meaning.
: To 'index' (a case/disease). It means to record, catalog, or designate something systematically, often as part of an investigation.
: Through epidemiological detective work: interviewing patients, tracing their contacts, and using laboratory data (like genetic sequencing of the pathogen) to build a transmission chain back to the earliest known case.