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What're the complications of influenza?

In general, the flu is usually self-limited and not serious. Influenza is responsible, however, for 15% to 30% of the excess number of hospitalizations that occur in winter. About 1% of people who contract the flu end up in the hospital and, on average, 20,000 Americans die every year from complications of influenza. Influenza complications usually arise from

bacterial infections of the lower respiratory tract.

Influenza may increase the risk for death in people with existing heart, lung, or circulation disorders. In fact, the higher than average number of winter deaths in people with heart disease may be due only to the occurrence of influenza during those months. Influenza can be dangerous to the elderly, especially those who live in residential homes where there is more risk of contracting the virus through contact with others. People with lung and heart diseases are also more likely to develop complications due to an attack of flu. Those at risk are advised to get a yearly vaccination.

Pneumonia is the major serious complication of influenza. It can develop about five days after viral influenza. It is an uncommon event, however, and nearly always occurs in susceptible individuals about five days after onset. This can be viral pneumonia, in which the influenza virus itself spreads into the lungs, or bacterial pneumonia, in which unrelated bacteria (such as pneumococci) attack the person's weakened defenses. In both cases, the person may have a worsened cough, difficulty breathing, persistent or recurring fever, and sometimes bloody sputum. Pneumonia is more common in older people and in people with heart or lung disease. As many as 7% of older people in long-term care facilities who develop influenza have to be hospitalized, and 1 to 4% die. Younger people with chronic illnesses are also at risk of developing severe complications.

Children under 1 years old have a very high risk, not only for pneumonia but also for other complications, including meningitis and encephalitis (inflammations in central nervous system). The risk declines after age one but is still elevated in children aged three to five. It is often difficult to tell whether pneumonia in small children is related to influenza or caused by respiratory syncytial virus (RSV), the major viral cause of infant pneumonia. Experts estimate that about 25% of severe lung infections are due to influenza.

Every year, influenza strikes millions of people worldwide. Influenza epidemics are most serious when they involve a new strain against which most people are not immune. Such so-called pandemics can infect more than one fourth of the world's population within a three-month period.

More information on influenza (flu)

What is influenza (flu)? - Influenza (flu) is a respiratory infection caused by one of the influenza viruses that typically is spread by air or by direct contact.
How is influenza transmitted? - Influenza is spread through contact with droplets from the nose and throat of an infected person during coughing and sneezing.
What causes influenza? - The flu is caused by three types (strains) of viruses - influenza A, B and C. Influenza A is responsible for the deadly influenza pandemics.
What's the influenza virus? - The influenza virus is in a class of viruses known as orthomyoxoviruses, with myxo referring to the fact that they infect mucus membranes.
What're the risk factors for influenza? - All people 50 years of age and older are at increased risk for serious illness with the flu, or in contact with those at high risk, and should receive vaccine.
What're the complications of influenza? - Influenza complications usually arise from bacterial infections of the lower respiratory tract. Pneumonia is the major serious complication of influenza.
What are the symptoms of influenza? - Influenza can cause a variety of symptoms. Typical flu symptoms include headache, fever, chills, cough and body aches. Intestinal symptoms are uncommon.
How is influenza diagnosed? - Diagnosis of influenza (flu) is based on typical symptoms of fever, chills, headaches, cough and body aches. There are a variety of tests to detect influenza.
What is the treatment for influenza? - The main treatment for influenza (flu) is to rest adequately, drink plenty of fluids, and avoid exertion. Amantadine and rimantadine are effective against influenza A.
How to control or prevent influenza? - The preferred treatment for influenza, and most viral infections is prevention. The prevention can be achieved through vaccinations.
What's the influenza vaccine (flu vaccine)? - Vaccination is the principal measure for preventing influenza. Influenza vaccinations are given to millions annually.
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