Table 1. Case definitions, three international ILI definitions and one national ARI definition (used as inclusion criterion), GROG study, France, 2009–2014.

Definition	Type	Sudden onset	General symptoms	Respiratory symptoms
ECDC	ILI	Yes	At least one among: fever, feverishness, headache, malaise, myalgia	At least one among: cough, sore throata, shortness of breath
WHO	ILI	No	Fever ≥ 38 °C with onset within the last 10 days	Cough
CDC	ILI	Yes	Fever ≥ 100° F (37.8 °C)b Absence of a known cause other than influenza	At least one among: cough, sore throata
GROG	ARI	Yes	At least one among: fever ≥ 38 °C, headache, weakness, myalgia, chills	At least one among: cough, coryza, bronchitis, pharyngitis, shortness of breath, expectoration

ARI: Acute respiratory illness; CDC: Centers for Disease Control and Prevention; ECDC: European Centre for Disease Prevention and Control; GROG: Groupes Régionaux d’Observation de la Grippe; ILI: influenza-like illness; WHO: World Health Organization.

^a The sore throat symptom is not collected in the GROG network. For the purpose of this work, the variable was replaced by pharyngitis diagnosis.

^b Fever is defined in the GROG network as a temperature fever ≥ 100.4°F (38.0 °C). For the purpose of this work, fever ≥ 100° F (37.8 °C) was replaced by fever ≥ 100.4°F (38.0 °C).