Guide for considering influenza testing when influenza viruses are circulating in the community (regardless of influenza vaccination history). ¹Confirmation of influenza virus infection by diagnostic testing is not required for decisions to prescribe antiviral medication. Decision making should be based upon signs and symptoms consistent with influenza illness and epidemiologic factors. Initiation of empiric antiviral treatment should not be delayed while influenza testing results are pending. Antiviral treatment is clinically most beneficial when started as close to illness onset as possible. ²Signs and symptoms of uncomplicated influenza. ³Clinical manifestations and complications associated with influenza and persons who are at high risk of complications from influenza. ⁴All hospitalized patients with suspected influenza should be tested, as detection of influenza virus infection and prompt initiation of antiviral therapy are most clinically beneficial, and implementation of infection prevention and control measures is essential for prevention of nosocomial influenza outbreaks. ⁵Influenza testing may be used to inform decisions on use of antibiotics or continuation of antiviral medication, on need for further diagnostic tests, on consideration for home care, or on recommendations for ill persons living with others who are at high risk for influenza complications. ⁶Influenza testing may be required to inform decisions on infection control practices. ⁷Antiviral treatment is recommended for outpatients with suspected influenza who are at high risk for complications from influenza, or those with progressive disease not requiring hospital admission. Antiviral treatment of outpatients who are not at high risk for influenza complications can be considered based upon clinical judgment if presenting within 2 days of illness onset. Abbreviations: HF, heart failure; COPD, chronic obstructive pulmonary disease.