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See also:

  • Avian Flu
  • Pandemic (H1N1) 2009 Flu


The flu (also called influenza) is a viral infection that affects the respiratory system. It can cause mild-to-severe illness, and sometimes it can lead to death.

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The influenza virus causes the flu. In temperate climates each winter, the virus spreads around the world. The strains are usually different from one year to the next. While less likely, it is possible to get the flu when it is not flu season (especially in tropical climates).

The two main kinds of influenza virus are Type A and Type B. There is also a Type C, but it is less common and not as virulent.

Someone infected with the virus may sneeze or cough. This releases droplets into the air. If you breathe in infected droplets, you can become infected. You can also become infected by touching a contaminated surface. The virus is transferred from your hand when you touch your mouth or nose.

Risk Factors

Factors that increase your chance of getting the flu include:

  • Living or working in crowded conditions, such as nursing homes, schools, military forces, and daycare centers
  • Being physically or mentally disabled—people with disabilities may not be able to easily communicate their symptoms or may have trouble practicing preventive measures against the flu, putting them more at risk.

Certain groups of people are at a higher risk of developing complications from the flu. Risk factors for complications include:

  • Children younger than 5 years old
  • Adults aged 65 years and older
  • Being American Indian/Alaska Native
  • Certain health conditions, such as asthma, diabetes, or heart disease
  • A suppressed immune system
  • Pregnancy during the flu season
  • Age younger than 18 years old and receiving long-term aspirin therapy—may be at risk for Reyes syndrome
  • Living in nursing homes or other long-term care facilities
  • Obesity


If you have the flu, you might infect others one day before symptoms start and up to 5 days (sometimes more) after you become sick. This means you may be infecting others even before you know you are sick.

Symptoms usually start abruptly. They may include:

  • High fever and chills
  • Severe muscle aches
  • Severe fatigue
  • Headache
  • Decreased appetite or other gastrointestinal symptoms like nausea, vomiting, and diarrhea (more common in children than adults)
  • Runny nose, nasal congestion
  • Sneezing
  • Watery eyes or conjunctivitis
  • Sore throat
  • Cough
  • Swollen lymph nodes in the neck


You will be asked about your symptoms and medical history. Diagnosis of the flu is usually based on symptoms.

In some cases, your doctor may take samples from your nose or throat to confirm the diagnosis.


During recovery, it is important to rest as much as possible and drink plenty of fluids, including water, juice, or caffeine-free tea. The flu generally lasts 7-10 days. A cough or fatigue may last longer.

Other treatment may include:



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