Overview

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

Possible problems from the flu include:

• Pneumonia, which is an infection of the lungs. 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.
• Bronchiolitis. This is an inflammation of the small air passages. It affects infants and is the leading cause of serious lower respiratory illness.
• Sinusitis. This means the mucous membranes that line the inside of the nose and facial sinuses become infected and inflamed.
• Croup. Croup is a swelling or blockage in the windpipe. It causes hoarseness, a barking cough, a high-pitched sound when breathing in, and trouble breathing.
• Chronic obstructive pulmonary disease (COPD) symptoms may get worse.
• Inflammation of the heart muscle, the sac around the heart, or other muscles.