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Influenza case definitions

Clinical Criteria

Any person with at least one of the following clinical forms:

Influenza-like illness (ILI)

  • Sudden onset of symptoms


And at least one of the following four systemic symptoms:

  • Fever or feverishness
  • Malaise
  • Headache
  • Myalgia


And at least one of the following three respiratory symptoms:

  • Cough
  • Sore throat
  • Shortness of breath

 

Acute respiratory infection (ARI)

  • Sudden onset of symptoms


And at least one of the following four respiratory symptoms:

  • Cough
  • Sore throat
  • Shortness of breath
  • Coryza

And a clinician’s judgement that the illness is due to an infection

Laboratory Criteria

At least one the following four:

  • Isolation of influenza virus from a clinical specimen
  • Detection of influenza virus nucleic acid in a clinical specimen
  • Identification of influenza virus antigen by DFA test in a clinical specimen
  • Influenza specific antibody response

Sub-typing of the influenza isolate should be performed, if possible.

Epidemiological Criteria


An epidemiological link by human-to-human transmission.

Case Classification


Possible case:

Any person meeting the clinical criteria (ILI or ARI)

Probable case:

Any person meeting the clinical criteria (ILI or ARI) and with an epidemiological link

Confirmed case:

Any person meeting the clinical (ILI or ARI) and the laboratory criteria

 

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© European Centre for Disease Prevention and Control (ECDC) 2005 - 2014