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
  • Chronic obstructive pulmonary disease (COPD) getting worse.
  • 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

Related Information


ByHealthwise Staff
Primary Medical Reviewer E. Gregory Thompson, MD – Internal Medicine
Specialist Medical Reviewer Christine Hahn, MD – Epidemiology

Current as ofMarch 25, 2017