Information from the CDC:
Testing is not needed for all patients with signs and symptoms of influenza to make antiviral treatment decisions. Once influenza activity has been documented in the community or geographic area, a clinical diagnosis of influenza can be made for outpatients with signs and symptoms consistent with suspected influenza, especially during periods of peak influenza activity in the community.
CDC information about Diagnosing Flu:
https://www.cdc.gov/flu/about/qa/testing.htm
Learn more about Rapid Influenza Diagnostic Tests :
https://www.cdc.gov/flu/professionals/diagnosis/clinician_guidance_ridt.htm
