Influenza, also called the flu, is an infection of the upper airway caused by an influenza virus. Symptoms can include fever, headache, runny nose, sore throat, or cough. Every year there is a period of time where there are more outbreaks of the flu, this is called flu season. Flu season generally occurs during the fall, winter and early spring. The influenza vaccines protect against the viruses that cause influenza. To learn more about the flu and the flu vaccines, and to access flu-related information from your health authority, visit our Influenza (Flu) Season health feature.
A bacterial infection may develop following infection with viral influenza. Signs of a bacterial infection include:
Ear pain that lasts more than 24 hours or severe ear pain that lasts longer than 1 hour.
A sore throat that lasts longer than 2 to 3 days despite home treatment and does not "act" like a cold.
Sinus pain that persists despite 2 to 4 days of home treatment, especially if nasal drainage is coloured rather than clear and fever is also present.
Nasal drainage that changes from clear to coloured after 5 to 7 days of flu, while other symptoms (such as sinus pain or fever) are getting worse.
A cough that lingers more than 7 to 10 days after other symptoms have cleared, especially if it is bringing up mucus (productive).
Yellow, green, rust-coloured, or bloody mucus that is coughed up from the lungs, especially while other symptoms are getting worse. Mucus coughed up from the lungs is a more serious symptom than mucus that has drained down the back of the throat (post-nasal drip).
These infections may sometimes need treatment with antibiotics.
ByHealthwise Staff Primary Medical ReviewerE. Gregory Thompson, MD - Internal Medicine Brian O'Brien, MD, FRCPC - Internal Medicine Adam Husney, MD - Family Medicine Specialist Medical ReviewerChristine Hahn, MD - Infectious Disease, Epidemiology