Flu (Influenza) Symptoms
Symptom Checker: Symptoms & Signs Index
Medical Author: Melissa Conrad Stöppler, MD
Influenza viruses cause the flu (influenza), a viral disease of the respiratory tract. Characteristic symptoms are fever, cough, malaise, and headache. Other symptoms can occur, like nausea and vomiting, muscle aches, sore throat, and diarrhea. Symptoms of the flu usually last for one to two weeks.
Other conditions can sometimes cause similar symptoms, leading people to wonder if they really have the flu or a different condition. Haemophilus influenzae is a bacterium that was incorrectly considered to cause the flu until a virus was demonstrated to be the correct cause in 1933. This bacterium can cause lung infections in infants and children and can sometimes cause sinus or other infections. Other bacterial or viral infections, including the common cold, may cause symptoms similar to the flu. Sometimes, allergies produce severe respiratory symptoms as well. Symptoms of certain complications of the flu, such as pneumonia, produce similar symptoms.
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