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Flu (Influenza) Overview

What is influenza?
Influenza (also called flu) is a viral infection of the nose, throat, trachea, and bronchi (air passages). Outbreaks of flu occur almost every year, usually in late fall and winter.

Flu viruses cause more severe symptoms and can cause more severe medical problems than cold viruses. Older adults, people whose immune systems are impaired, and people with chronic medical problems are particularly at risk for more severe flu symptoms or complications.

How does it occur?
The flu virus is almost always spread from person to person by droplets that are coughed or sneezed into the air. It can also be spread by the hands of an infected person who has touched their mouth or nose.

What are the symptoms?
Influenza tends to start suddenly. You may feel fine one hour and have a high fever the next.

The usual first symptoms are:

  • chills and fever (often 101 to 103°F, or 38 to 40°C)
  • sweating
  • muscle aches
  • headache.

Symptoms soon to follow may include:

  • runny nose and nasal congestion
  • cough
  • sore throat
  • eyes sensitive to light.

How is it diagnosed?
Influenza can usually be diagnosed from your symptoms. Your healthcare provider may examine you to rule out other types of infection, such as strep throat and sinusitis.

How is it treated?
Usually you will recognize the symptoms and can manage them at home. Call your healthcare provider if you have symptoms of the flu and:

  • You have heart disease, asthma, chronic bronchitis, kidney disease, diabetes, or another chronic medical problem.
  • Your immune system does not work normally (for example, because you are taking steroids for another medical problem).
  • Your symptoms become more severe, you have a painful cough, you are coughing up phlegm, or you are having trouble breathing. These symptoms can be signs of pneumonia or bronchitis.

To take care of yourself at home:

  • Get plenty of rest.
  • Drink a lot of liquids. Water, juice, and noncaffeinated drinks are best. Especially when you have a high fever, your body needs much more liquid than when you are healthy. Having enough fluids also helps the mucus in your sinuses and lungs to stay thin and easy to clear from the body. When the mucus is thin, it is less likely to cause a sinus infection or bronchitis.
  • Consider taking acetaminophen or ibuprofen to relieve headaches and muscle aches and to lower a fever. Some healthcare providers feel that because fever is part of the immune system's reaction to infection, it is better to let a fever run its course than to try to lower it. Letting the fever run its course, however, can be dangerous in children and older adults. Also, most healthy adults feel much better if the fever is decreased even just 1 or 2 degrees.

    Children under 18 years of age should not take aspirin or products containing salicylate (such as Pepto-Bismol) because of the risk of Reye's syndrome unless recommended by a healthcare provider.
  • If your nose or sinuses become congested, a decongestant medicine may help you feel better and may possibly help prevent ear or sinus infections.
  • Take cough medicine to help control your cough.
  • Antihistamine medicine can be helpful if a runny nose is making it hard for you to sleep. However, antihistamine has a very drying effect and may cause the mucus in your nose, throat, and lungs to become thick and dry.

There are medicines your healthcare provider can prescribe that can make flu symptoms less severe. They may also help the symptoms not last as long. Examples of these drugs are zanamivir (Relenza) and oseltamivir (Tamiflu). These flu medicines are available as tablets or nasal sprays. They must be started within the first 48 hours of illness to be effective. Usually they need to be taken only a few days. A common side effect of the tablets is lightheadedness or dizziness.

How long will the effects last?
Flu symptoms usually last 3 to 7 days. They often start improving gradually after the first 2 days or so.

Infection with the flu virus often leads to other infections, such as ear, sinus, and bronchial infections. Pneumonia can also occur as a result of the flu. It can be caused by the flu virus itself or by bacteria invading lung tissues that have been damaged by the virus. Pneumonia is a common cause of death in people over the age of 65 and often occurs during and after flu outbreaks.

An unusual complication of flu is Reye's syndrome, which usually occurs in children and adolescents and rarely occurs in adults. Reye's syndrome is not well understood but it involves failure of the liver and brain swelling, which together can lead to coma and sometimes death. A link has been shown between the use of aspirin during influenza illness and the development of Reye's syndrome. For this reason it is best to avoid taking aspirin and other salicylates when you have the flu.

What can I do to prevent influenza?
Flu shots help prevent the flu. Because the flu virus strain varies from year to year, you need to get a new flu shot each year. October is the best time to get vaccinated, but you can still get vaccinated in November and later. Flu season can begin as early as October and last as late as May. Flu seasons can vary from region to region. If you are at high risk for infection and plan to travel to an area where you might be exposed to the flu, make sure you have an up-to-date flu shot before you go on your trip.

If you do get the flu even though you had your annual shot, the vaccine helps protect against severe and possibly life-threatening infection.

A new alternative to flu shots is FluMist. It is a nasal spray form of the vaccine for healthy adults under age 50. It costs more than the shot. As with flu shots, you will need a new dose of FluMist every year. Pregnant women cannot take the nasal spray. Also, people with certain other medical conditions should not take FluMist. If you are considering using FluMist, ask your provider if it is recommended for you.

If a flu outbreak has begun and you have not had the flu vaccine and need some protection, your healthcare provider may prescribe medicine that can decrease your chances of getting the flu during the outbreak. You will need to take these medicines for at least 2 weeks after you are vaccinated. If you don't get the vaccine, you need to take the medicine until the flu outbreak has left your community, which may be several weeks. If you do get the flu, the medicines can make your symptoms less severe.

The simplest, oldest method of avoiding spread of infection is frequent hand washing, preferably with soap from a sanitary dispenser. It is also a good practice not to eat in or near your workplace. Your hands or food might be contaminated with the virus particles from co-workers, customers, or schoolchildren, depending on your place of work.