Health information exchange; influenza; surveillance (3), a resource developed by a working group of 18 researchers representing 10 syndromic surveillance systems in North America. ESSO encodes almost three times as many clinical concepts as the Syndromic Surveillance Ontology and incorporates eight syndrome categories, in contrast to the Syndromic Surveillance Ontology's four (influenza-like illness, constitutional, respiratory and gastrointestinal). The new clinical concepts and syndrome groupings in ESSO were developed by a board-certified infectious disease physician (author JD) in conjunction with an informaticist (author MC). In order to evaluate and audit these new syndrome definitions, we initiated a survey of syndromic surveillance practitioners.