Six jurisdictions provided 4 years of baseline ED data using a common ILI definition comprising 3 subsyndrome components defined by a formal code-set (Fig. 1) . Distribute sites were invited to participate in the assessment based on geography, jurisdiction size and ED coverage. Invited sites were asked to provide historical data consisting of total and ILI-related daily visit counts by age group ( B2, 2Á4, 5Á17, 18Á44, 45Á64 and 65' years). The common ILI syndrome and subsyndrome case definitions for the pilot were defined from coded or free text ED patient electronic chief complaint data as 'fever and cough', 'fever and sore throat', and 'flu'. Evaluation included comparison of syndrome time-series, subsyndrome and age-specific distribution of visits and signal-to-noise measures.