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Flu: Complications
Many people can fight flu symptoms with lots of rest and fluids, but certain high-risk groups may experience dangerous complications as a resul...

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Flu: Complications

The flu is relatively common—the U.S. Department of Health and Human Services (DHHS) reports that the seasonal flu affects up to 20 percent of Americans each year. While many people can combat symptoms with plenty of rest and fluids, certain high-risk groups may experience dangerous and even life-threatening complications as a result of the flu.

The Centers for Disease Control and Prevention (CDC) estimate that between 3,000 and 49,000 people in the United States die each year from the flu. The World Health Organization (WHO) estimates that each year between a quarter to half a million people worldwide die from flu complications.

According to a CDC study published in the Journal of the American Medical Association, an average of 200,000 Americans required hospital care each year (from 1979 to 2001) for respiratory and heart complications due to the flu virus.

The study also found that flu-related hospital visits increased with each year. One flu season, the number reached 430,960.

Those at High Risk for Flu Complications

The following groups are at higher risk for the flu. According to the CDC, these groups should receive first priority when there is a shortage of flu vaccine.

High-risk individuals include those:

  • between six months and five years of age
  • 65 and older
  • who are pregnant
  • children and teens under 19 who receive aspirin therapy
  • with weakened immune systems due to disease (such as cancer or HIV/AIDS) or long-term steroid medication use
  • whose body mass index is 40 or higher
  • with asthma
  • with heart and lung conditions
  • with other chronic health conditions, including metabolic disorders, kidney disorders, blood disorders (sickle cell anemia), liver disorders, endocrine disorders (diabetes), and those with neurological and neurodevelopmental disorders (epilepsy, stroke, cerebral palsy)

Native Americans and Alaskan Natives are also at greater risk for flu complications.

These groups should monitor their flu symptoms closely. They should also seek immediate medical care at the first sign of complications.

Flu and Those 65 and Over

People 65 and over are at greatest risk for flu-related complications and death. The CDC estimates that more than 60 percent of flu-related hospital stays and 90 percent of flu-related deaths occur in this age group.

This is why it is so important for these individuals to receive a flu shot.

The flu shot’s ability to prevent flu may lessen a bit with age. This is because the immune system’s response declines as we get older.

Still, the flu shot remains the best way to prevent flu and its related complications.

The U.S. Food and Drug Administration (FDA) recently approved a higher-dose vaccine, FluZone High-Dose, for those 65 and over.

This vaccine contains four times the amount of antigens as the normal flu vaccine. Antigens stimulate the immune system’s production of antibodies, which fight the flu virus.

Complications of the Flu

Complications of the flu will often appear just as main flu symptoms are subsiding. The flu can also make already-present health conditions worse.

The following complications may develop from the flu:


Pneumonia is a bacterial infection that causes the lungs to become inflamed. This causes symptoms of cough, fever, shaking, chills, and other side effects.

It is the most common complication of the flu, and can be especially dangerous—sometimes deadly—for people in high-risk groups. These groups include the very young, the elderly, and those with existing medical conditions.

Seek medical treatment immediately if you have any of the following symptoms:

  • severe cough with large amounts of mucus
  • trouble breathing
  • shortness of breath
  • fever higher than 102°F that is not going away—especially if chills or sweating are also present
  • chest pains
  • severe chills or sweating

This condition is typically highly treatable, often with simple home remedies like sleep and plenty of warm fluids.  However, the Mayo Clinic points out that smokers, older adults, and people with heart or lung problems are especially prone to complications associated with this condition. Further complications from pneumonia include fluid buildup in and around the lungs, bacteria in the bloodstream, and acute respiratory distress syndrome.


This complication is caused by irritation of the mucous membranes of the bronchi in the lungs.

Symptoms of bronchitis include cough (often with mucus), chest tightness, fatigue, mild fever, and chills.

Most often, simple remedies such as rest, drinking plenty of fluids, using a humidifier, and taking over-the-counter pain medications are all that’s needed to treat this complication.

However, contact your doctor if you have any of the following symptoms:

  • a cough that lasts longer than three weeks
  • a cough that interrupts your sleep
  • a cough combined with fever over 100.4°F
  • a cough that produces mucus of a strange color
  • a cough that produces blood
  • a cough combined with wheezing or difficulty breathing

More serious conditions such as pneumonia, emphysema, heart failure, and pulmonary hypertension can develop from untreated, chronic bronchitis.


Sinusitis is the swelling of the sinuses. Symptoms include nasal congestion, sore throat, postnasal drip, pain in the sinuses, pain in the upper jaw and teeth, a reduced sense of smell or taste, and cough.

Sinusitis can often be treated with over-the-counter saline spray, decongestants, and pain relievers. Your doctor may also prescribe a nasal corticosteroid like fluticasone (Flonase) or mometasone (Nasonex) to reduce inflammation. 

Symptoms that warrant immediate medical attention include:

  • pain or swelling near the eyes
  • swollen forehead
  • severe headache
  • mental confusion
  • vision changes, such as seeing double
  • difficulty breathing
  • neck stiffness

These may be signs of sinusitis that has worsened or spread.

Otitis Media

Better known as an ear infection, this condition is an infection and swelling of the ear.

Symptoms include chills, fever, hearing loss, ear drainage, vomiting, and mood changes.

According to the Mayo Clinic, an adult with ear pain or discharge should see his or her doctor as soon as possible. A child should be taken to his or her doctor if:

  • symptoms last more than one day
  • ear pain is extreme
  • you notice discharge from the child’s ear
  • your child is not sleeping or is moodier than usual


This rare condition occurs when a flu virus enters the brain tissue and causes swelling of the brain, which can lead to destroyed nerve cells, bleeding in the brain, and brain damage.

Symptoms include severe headache, high fever, vomiting, light sensitivity, drowsiness, and clumsiness.

Though rare, this condition may also cause tremors and difficulty with movement.

Seek medical care immediately if you have any of the following symptoms:

  • severe headache or fever
  • mental confusion
  • hallucinations
  • severe mood changes
  • seizures
  • paralysis
  • double vision
  • speech or hearing problems

Symptoms of this condition in young children include:

  • protrusion in the soft spots on an infant’s skull
  • body stiffness
  • uncontrollable crying
  • crying that gets worse when the child is picked up
  • loss of appetite
  • vomiting and nausea

Worsening of Existing Conditions

The flu can also worsen existing conditions, such as heart, lung, kidney, or liver disease.

Long-Term Outlook for Those Who Develop Flu-Related Complications

A yearly flu vaccine is the best preventative measure for those at high risk of flu-related complications. Practicing good hygiene such as regular hand washing and avoiding or limiting contact with infected people can also help prevent the spread of the flu.

Early treatment is also key to successfully treatment of flu-related complications. Most of the complications mentioned above respond well to treatment. However, many can become more serious without proper treatment. 

Most flu symptoms resolve within one to two weeks. If your flu symptoms worsen or do not subside after two weeks, call your doctor. 

Written by: the Healthline Editorial Team
Edited by:
Medically Reviewed by:
Published: Jul 28, 2014
Published By: Healthline Networks, Inc.
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