Content Map Terms

Influenza (Flu) Complications

British Columbia Specific Information

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. 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.

The symptoms of flu are similar to other respiratory illnesses including the common cold and COVID-19. Use the BC COVID-19 Self-Assessment Tool to find out if you or your family members need further assessment or testing for COVID-19. To learn more about the coronavirus, symptoms, how it spreads and prevention visit the Coronavirus (COVID-19) health feature.

Topic Overview

Although most cases of influenza (flu) get better without causing other problems, complications sometimes develop.

Possible complications of flu include:

  • Pneumonia, which is an inflammation of the lungs.
    • Primary influenza viral pneumonia develops soon (24 to 36 hours) after flu symptoms start and does not get better with antibiotics. It rarely causes death in young, healthy people, but it can often be life-threatening in older adults, people who have other diseases, and pregnant women.
    • Secondary bacterial pneumonia most often develops after a period of improvement following the flu. People with this type of pneumonia usually get better with antibiotics.
  • Bronchiolitis, which is an inflammation of the small air passages (bronchioles). Bronchiolitis affects infants and is the leading cause of serious lower respiratory illness.
  • Sinusitis, which is an infection or inflammation of the mucous membranes that line the inside of the nose and facial sinuses. Facial sinuses are hollow spaces, or cavities, located around the eyes, cheeks, and nose.
  • Croup, which is a swelling or obstruction in the windpipe (trachea). It causes a distinctive hoarseness and a barking cough, a high-pitched sound (stridor) heard when breathing in, and trouble breathing.
  • Worsening of chronic obstructive pulmonary disease (COPD).
  • Reye syndrome, which is a very rare but serious disease that most often occurs in children 6 to 12 years old. The exact cause is not known. But it is associated with children who have recently had chickenpox (varicella) or flu (influenza) and have taken aspirin. The disease primarily targets the brain and liver and can cause drowsiness, confusion, seizures, coma, and in severe cases, death.
  • Inflammation of the heart muscle (myocarditis), inflammation of muscles (myositis), or inflammation of the sac around the heart (pericarditis).
  • Fatigue and a lack of energy that persist after flu symptoms are gone. People may take several weeks to fully recover, although no cause for the symptoms has been identified.

Credits

Current as of:
July 6, 2021

Author: Healthwise Staff
Medical Review:
E. Gregory Thompson MD - Internal Medicine
Brian D. O'Brien MD - Internal Medicine
Adam Husney MD - Family Medicine
Christine Hahn MD - Epidemiology