What are the signs and symptoms of influenza?

Updated: Apr 23, 2019
  • Author: Hien H Nguyen, MD, MS; Chief Editor: Michael Stuart Bronze, MD  more...
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Answer

The presentation of influenza virus infection varies; however, it usually includes many of the symptoms described below. Patients with influenza who have preexisting immunity or who have received vaccine may have milder symptoms.

Onset of illness can occur suddenly over the course of a day, or it can progress more slowly over the course of several days. Typical signs and symptoms include the following (not necessarily in order of prevalence):

  • Cough and other respiratory symptoms

  • Fever

  • Sore throat

  • Myalgias

  • Headache

  • Nasal discharge

  • Weakness and severe fatigue

  • Tachycardia

  • Red, watery eyes

Cough and other respiratory symptoms may be initially minimal but frequently progress as the infection evolves. Patients may report nonproductive cough, cough-related pleuritic chest pain, and dyspnea. In children, diarrhea may be a feature.

Fever may vary widely among patients, with some having low fevers (in the 100°F range) and others developing fevers as high as 104°F. Some patients report feeling feverish and feeling chills.

Sore throat may be severe and may last 3-5 days. The sore throat may be a significant reason why patients seek medical attention.

Myalgias are common and range from mild to severe. Frontal or retro-orbital headache is common and is usually severe. Ocular symptoms develop in some patients with influenza and include photophobia, burning sensations, or pain upon motion. Some patients with influenza develop rhinitis of varying severity, but it is generally not the chief symptom.


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