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Symptoms and Signs of Flu in Adults

Doctor's Notes on Flu in Adults

Flu, or influenza, is an upper respiratory infection caused by influenza viruses. There are many different types of influenza viruses, so it is possible to develop the disease multiple times. The viral infection is contagious and people acquire the infection from contact with infected people or objects.

Signs and symptoms of a mild case of the flu may resemble those of a severe cold and can include runny or stuffy nose, cough, sneezing, fatigue, malaise, and headache. With influenza, fever is more likely to occur, and it may be high. Other possible associated symptoms can include weight loss, loss of appetite, weakness, nausea, vomiting, diarrhea, and sore throat. If vomiting or diarrhea are present, symptoms of dehydration may develop.

Medical Author:
Medically Reviewed on 3/11/2019


Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.