Complications of Flu

The flu itself can be a serious illness with severe symptoms. Some people require hospitalization and fatality is possible from flu, especially in young children, the elderly, or people with other chronic diseases. The list of at-risk patients includes:

Simple Infectious Complications: Some of the possible complications of flu include the same types of complications that often occur with the common cold (or any other URTI), such as:

Severe Flu Complications: There are also very severe possible complications from flu:

Pre-Existing Chronic Illness: Exacerbation of other medical diseases by a flu infection can also be a serious complication. Take extra care if the patient has a pre-existing chronic condition, such as:

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Complications of Flu

Bronchitis, pneumonia; can be life-threatening

Source: NIH News in Health (NIH)1

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Each year, seasonal influenza sickens millions and causes thousands of hospitalizations and flu-related deaths. Even healthy people can get very sick from the flu and spread it to others. Flu infection can present particularly serious problems for young children, the elderly, pregnant women and people with certain medical conditions, such as asthma and heart disease.

Source: NIAID (NIH)2

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Some people are at greater risk for flu complications, like young children and adults 65 years and older.

Grandfather with granddaughter on shoulders

Some people are at greater risk for flu complications, like young children and adults 65 years and older.

Who Is at Risk?

Everyone is at risk for getting the flu. For millions of people each year, the flu can cause a fever, cough, sore throat, runny or stuffy nose, muscle aches, headache, chills and fatigue. But for some people, the flu can be more severe. CDC estimates that since 2010, flu-related hospitalizations in the United States ranged from 140,000 to 710,000 people and flu-related deaths have ranged from 12,000 to 56,000 people.

Some people are at greater risk for serious flu-related complications like pneumonia or worsening of existing chronic health conditions. For those at greater risk for complications, it's especially important to get vaccinated every season. It's also important for those people to check with a doctor promptly about taking antivirals if flu symptoms develop.

Source: CDC Features3

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Vaccination against the flu is especially important for American Indians and Alaska Natives, who have been found to be at high risk for developing complications from the flu.

Additionally, within the community there are certain people that have a greater chance of becoming severely ill from influenza infection and complications, either because of their age or certain health conditions. This includes:

Source: CDC Features4

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Complications of influenza virus infection include primary influenza viral pneumonia, secondary bacterial pneumonia, exacerbation of underlying medical conditions (such as pulmonary and cardiac disease), encephalopathy, myocarditis, myositis, and coinfections with other viral or bacterial pathogens.

Source: CDC Yellow Book 20165

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What should cancer patients and survivors do if they think they may have the flu?

If you have received cancer treatment such as chemotherapy and/or radiation therapy within the last month, or have a blood or lymphatic form of cancer, call your doctor immediately if you get flu symptoms. Learn how to prevent infections while you’re receiving chemotherapy.

All cancer patients and survivors should follow the steps below.

  1. Contact your health care provider and follow his or her instructions.
  2. Stay home and away from others as much as possible to keep from making them sick. This means you should avoid public activities, including work, school, travel, shopping, social events, and public gatherings. You should stay home for at least 24 hours after your fever is gone (without the use of fever-reducing medicine), except to get medical care or other necessities.
  3. If you need to go to the doctor’s office, emergency room, or any other health care facility, cover your mouth and nose with a facemask, if available and tolerable, or cover your mouth and nose with a tissue when coughing or sneezing. Let the facility’s staff know you are there because you think you may have the flu.

Source: CDC Cancer6

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Flu Complications

Most people who get influenza will recover in a few days to less than two weeks, but some people will develop complications (such as pneumonia) as a result of the flu, some of which can be life-threatening and result in death.

Pneumonia, bronchitis, sinus and ear infections are examples of complications from flu. The flu can make chronic health problems worse. For example, people with asthma may experience asthma attacks while they have the flu, and people with chronic congestive heart failure may experience worsening of this condition that is triggered by the flu.

Source: CDC7

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People at High Risk from Flu

Anyone can get the flu (even healthy people), and serious problems related to the flu can happen at any age, but some people are at high risk of developing serious flu-related complications if they get sick. This includes people 65 years and older, people of any age with certain chronic medical conditions (such as asthma, diabetes, or heart disease), pregnant women, and young children.

Source: CDC8

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It can cause mild to severe illness. Serious outcomes of flu infection can result in hospitalization or death. Some people, such as older people, young children, and people with certain health conditions, are at high risk for serious flu complications.

Source: CDC9

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Flu Complications

Most people who get influenza will recover in several days to less than two weeks, but some people will develop complications as a result of the flu. A wide range of complications can be caused by influenza virus infection of the upper respiratory tract (nasal passages, throat) and lower respiratory tract (lungs). While anyone can get sick with flu and become severely ill, some people are more likely to experience severe flu illness. Young children, adults aged 65 years and older, pregnant women, and people with certain chronic medical conditions are among those groups of people who are at high risk of serious flu complications, possibly requiring hospitalization and sometimes resulting in death. For example, people with chronic lung disease are at higher risk of developing severe pneumonia.

Sinus and ear infections are examples of moderate complications from flu, while pneumonia is a serious flu complication that can result from either influenza virus infection alone or from co-infection of flu virus and bacteria.

Other possible serious complications triggered by flu can include inflammation of the heart (myocarditis), brain (encephalitis) or muscle (myositis, rhabdomyolysis) tissues, and multi-organ failure (for example, respiratory and kidney failure).

Flu virus infection of the respiratory tract can trigger an extreme inflammatory response in the body and can lead to sepsis, the body’s life-threatening response to infection.

Flu also can make chronic medical problems worse. For example, people with asthma may experience asthma attacks while they have the flu, and people with chronic heart disease may experience a worsening of this condition triggered by flu.

Source: CDC10

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For some people, such as the elderly and those with underlying medical conditions, the flu can cause serious complications which require hospitalisation. It can sometimes lead to death.

Source: Queensland Health11

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Health outcome

Most people recover from the flu within a week, although a cough and tiredness may persist.

Serious complications of flu occur in a small proportion of people who are infected and include pneumonia, inflammation of the heart muscle and neurologic complications, which can lead to hospitalisation and death. People at highest risk of complications from flu include those with pre-existing medical conditions. However, previously healthy people can also have severe complications.

For young children and the elderly, flu is one of the most common vaccine preventable causes of hospitalisation.

Source: Queensland Health12

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How serious is the flu?

Certain people are at greater risk for serious complications if they get the flu. This includes older people, young children, pregnant women, and people with certain health conditions (such as asthma, diabetes, or heart disease), and persons who live in facilities like nursing homes.

Flu seasons are unpredictable and can be severe. Over a period of 30 years, between 1976 and 2006, estimates of flu-associated deaths in the United States range from a low of about 3,000 to a high of about 49,000 people.

Source: MedLinePlus Magazine (NIH)13

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Older people, young children, pregnant women, and people with certain medical conditions are at a higher risk of developing serious complications from influenza, such as pneumonia. If you’re at higher risk, it is important to see your doctor early, to find out if you need treatment.

It is also important to seek medical advice early if you are concerned, and especially if there are any danger signs, even if you have been seen before.

Source: New Zealand Health14

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Call 999 or go to A&E if you:

Source: NHS Choices UK15

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Complications include bacterial pneumonia, and can be life threatening especially in:

  • older people
  • those with certain underlying health conditions

Source: GOV.UK16

Complications for Flu

Congenital heart disease: Women who get flu during the first trimester (three months) of pregnancy are twice as likely to give birth to a baby with congenital heart disease than the general population. The reasons for this are unclear.

The flu vaccine is recommended for all pregnant women.

Source: NHS Choices UK17

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Labyrinthitis: Labyrinthitis usually follows a viral infection, such as a cold or the flu. The infection can spread from the chest, nose, mouth and airways to the inner ear.

Source: NHS Choices UK18

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Reye's syndrome: You should contact your GP if, after having a cold, flu or chickenpox, your child is:

Although it's unlikely these symptoms will be caused by Reye's syndrome, they still need to be checked by a doctor.

Tell your GP if your child has taken aspirin, because the use of aspirin in children has been linked to Reye's syndrome (see below).

But even if your child hasn't taken aspirin, Reye's syndrome shouldn't be ruled out.

Source: NHS Choices UK19

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Stillbirth: Other infections that can cause stillbirths include:

  • flu - it's recommended that all pregnant women have the seasonal flu vaccine, regardless of stage of pregnancy

Source: NHS Choices UK20

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De Quervain's thyroiditis: De Quervain's (subacute) thyroiditis is a painful swelling of the thyroid gland thought to be triggered by a viral infection, such as mumps or the flu.

Source: NHS Choices UK21

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  1. Source: NIH News in Health (NIH): issue/ oct2014/ feature2
  2. Source: NIAID (NIH): diseases-conditions/ influenza
  3. Source: CDC Features: Features/ FluPrevention/ index.html
  4. Source: CDC Features: features/ AIANFlu/ index.html
  5. Source: CDC Yellow Book 2016: travel/ yellowbook/ 2016/ infectious-diseases-related-to-travel/ influenza
  6. Source: CDC Cancer: cancer/ flu/ symptoms.htm
  7. Source: CDC: flu/ consumer/ symptoms.htm
  8. ibid.
  9. Source: CDC: flu/ about/ disease/ index.htm
  10. Source: CDC: flu/ about/ disease/ complications.htm
  11. Source: Queensland Health: HealthCondition/ condition/ 8/ 118/ 82/ influenza-the-flu
  12. ibid.
  13. Source: MedLinePlus Magazine (NIH): magazine/ issues/ fall14/ articles/ fall14pg10-11.html
  14. Source: New Zealand Health: your-health/ conditions-and-treatments/ diseases-and-illnesses/ influenza
  15. Source: NHS Choices UK: conditions/ Flu/ 
  16. Source: GOV.UK: government/ collections/ seasonal-influenza-guidance-data-and-analysis
  17. Source: NHS Choices UK: conditions/ congenital-heart-disease/ causes/ 
  18. Source: NHS Choices UK: conditions/ Labyrinthitis/ 
  19. Source: NHS Choices UK: conditions/ Reyes-syndrome/ 
  20. Source: NHS Choices UK: conditions/ stillbirth/ causes/ 
  21. Source: NHS Choices UK: conditions/ thyroiditis/ 

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Note: This site is for informational purposes only and is not medical advice. See your doctor or other qualified medical professional for all your medical needs.