Influenza

WHO surveillance case definitions for ILI and SARI

Case definitions for influenza surveillance

As of January 2014

The WHO global influenza surveillance standards define the surveillance case definitions for influenza-like illness (ILI) and severe acute respiratory infections (SARI).

Key messages when using the case definitions:

  • Influenza infection causes a clinical syndrome not easily distinguished from other respiratory infections.
  • The case definitions for ILI and SARI are not necessarily intended to capture all cases but to describe trends over time.
  • Using one common case definition globally will allow national health authorities to interpret their data in an international context.

ILI case definition

An acute respiratory infection with:

  • measured fever of ≥ 38 C°
  • and cough;
  • with onset within the last 10 days.

SARI case definition

An acute respiratory infection with:

  • history of fever or measured fever of ≥ 38 C°;
  • and cough;
  • with onset within the last 10 days;
  • and requires hospitalization.
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