From the source paper that is being referenced (from Nature): > During seasonal influenza epidemics, diagnosis on the basis of clinical presentation has reason

From the source paper that is being referenced (from Nature): > During seasonal influenza epidemics, diagnosis on the basis of clinical presentation has reasonable accuracy in previously healthy young and middle-aged adults, in whom the presence of fever with either cough or sore throat is associated with influenza virus infection in ~80% of patients. So Wikipedia doesn’t add that this statement is about the accuracy of diagnosis by a clinician, and completely ignores the important symptom of a fever. Just prior to the statement referring to 80%, Wikipedia also states the following, with references: > In a typical year, influenza viruses infect 5–15% of the global population