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

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

An epidemiological link by human to human transmission

• 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