Table 1. Case definitions tested for accuracy of respiratory syncytial virus detection through the sentinel influenza surveillance system, Portugal, 2010–2018 .

Case definition	Sudden onset of symptoms	Respiratory symptoms	Systemic symptoms
ILI (EU, 2012)	Yes	At least one among: cough, sore throat or shortness of breath	At least one among: fever or feverishness, malaise, headache, myalgia
ARI-likea (EU, 2012)	Yes	At least one among: cough, sore throat or shortness of breath	No
One respiratory symptom	No	At least one among: cough, sore throat or shortness of breath	No

ARI: acute respiratory infection; EU: European Union; ILI: influenza-like illness.

^a The EU case definition for ARI includes coryza in the group of respiratory symptoms, as well as the clinician’s judgement that the illness is due to an infection. In this study, coryza and the clinician’s judgement were not included in the ARI-like case definition because they were not collected in the Portuguese Influenza Surveillance System.