Abstract
International case definitions recommended by the Centers for Disease Control and Prevention (CDC), the European Centre for Disease Prevention and Control (ECDC), and the World Health Organization (WHO) are commonly used for influenza surveillance. We evaluated clinical factors associated with the laboratory-confirmed diagnosis of influenza and the performance of these influenza case definitions by using a complete dataset of 14,994 patients with acute respiratory infection (ARI) from whom a specimen was collected between August 2009 and April 2014 by the Groupes Régionaux d’Observation de la Grippe (GROG), a French national influenza surveillance network. Cough and fever ≥ 39 °C most accurately predicted an influenza infection in all age groups. Several other symptoms were associated with an increased risk of influenza (headache, weakness, myalgia, coryza) or decreased risk (adenopathy, pharyngitis, shortness of breath, otitis/otalgia, bronchitis/ bronchiolitis), but not throughout all age groups. The WHO case definition for influenza-like illness (ILI) had the highest specificity with 21.4%, while the ECDC ILI case definition had the highest sensitivity with 96.1%. The diagnosis among children younger than 5 years remains challenging. The study compared the performance of clinical influenza definitions based on outpatient surveillance and will contribute to improving the comparability of data shared at international level.
Highlights
According to the 2011 World Health Organization (WHO) guidelines, an influenza surveillance system aims to reliably detect the start and duration of the influenza season in order to monitor changes in the antigenicity of influenza viruses and provide guidance for influenza vaccine policies [1]
A variety of national case definitions are applied in surveillance networks worldwide, in addition to international influenza-like illness (ILI) case definitions used by the United States (US) Centers for Disease Control and Prevention (CDC), the European Centre for Disease Prevention and Control (ECDC), and the WHO, which complicates data aggregation and comparison [2]
Based on the data collected between 2009 and 2014 by the Groupes Régionaux d’Observation de la Grippe (GROG), a French national influenza surveillance network, this study aimed to analyse clinical and non-clinical factors associated with the diagnosis of influenza and to compare the performance of international clinical case definitions
Summary
According to the 2011 World Health Organization (WHO) guidelines, an influenza surveillance system aims to reliably detect the start and duration of the influenza season in order to monitor changes in the antigenicity of influenza viruses and provide guidance for influenza vaccine policies [1]. The system should provide continuous and robust data in order to monitor trends of clinically diagnosed influenza-like illness (ILI) and assess its disease burden in the general and high-risk population. The search for the optimal case definition remains a public health challenge because of the lack of specificity of influenza symptoms, co-circulation of other respiratory viruses and low proportion of laboratory confirmation. In addition to the established ILI case definitions, some surveillance systems use acute respiratory illness (ARI), a more sensitive but in exchange less specific case definition [2]. French influenza surveillance networks each have their own ILI definitions, which differ in the combination of clinical symptoms [2].
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