Influenza is a viral infection of the respiratory tract that causes coughing, breathing difficulty, fever, headache, muscle aches and weakness. The virus is spread from person to person by inhaling infected droplets from the air.
Review Date: 8/14/2015
Reviewed By: Linda J. Vorvick, MD, Medical Director and Director of Didactic Curriculum, MEDEX Northwest Division of Physician Assistant Studies, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.