Snapshot A 26-year-old woman presents to the emergency room for 3 days of high fever, chills, muscle aches, a severe headache, and sore throat. She works in a nursing home but has not had her flu shot yet this year. She has a past medical history of systemic lupus erythematosus and hypothyroidism. A rapid strep test is negative, and a rapid antigen detection test for flu is positive. She is started on oseltamivir for this infection. Introduction Classification login to view 4 more bullets Epidemiology login to view 10 more bullets Etiology login to view 4 more bullets Pathogenesis login to view 4 more bullets Genetics login to view 5 more bullets Prevention login to view 5 more bullets Prognosis login to view 3 more bullets Presentation Symptoms login to view 6 more bullets Physical exam login to view 1 more bullet Imaging Chest radiography login to view 5 more bullets Studies Labs login to view 3 more bullets Making the diagnosis login to view 1 more bullet Differential Upper respiratory infection login to view 2 more bullets Treatment Management approach login to view 3 more bullets Conservative login to view 6 more bullets Medical login to view 3 more bullets Complications Secondary bacterial infection Myositis or myocarditis Central nervous system involvement