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Article on "Influenza (Flu)"  

Influenza (Flu)


Influenza, commonly referred to as “flu”, is a contagious disease caused by Influenza virus. Influenza virus is transmitted through breathing air that contains the infective virus. The viruses are present in the air in form of aerosols, which are fine solid particles or liquid droplets suspended in the air. The aerosols that contain Influenza virus are released into the air whenever a person coughs or sneezes. 

Influenza is common in winters and it can infect any age group.

The affected person may develop fever, cough, sore throat, headache, bodyache, and weakness. The infection usually resolves by itself within a week or two and even without treatment. It is a self-limiting condition. But in some cases, severe symptoms such as shortness of breath or high fever may occur due to associated conditions such as Pneumonia.

Quick Points About the Disease/Condition

Contagious, acute (short term disease), non-genetic, non-fatal.

Your Body Part or System That it Affects

Throat, Lungs.

Causes of Influenza (Flu)

People with Influenza release aerosols containing Influenza virus into the air when they cough or sneeze. These aerosols may be inhaled by others, which is called air borne transmission.

These aerosols may also deposit on the surface of blankets, clothes, doorknobs, light switches, or other objects. Touching these surfaces transmits the virus on to the hands. This can happen by personal contact with an infected person, such as shaking hands. Putting an infected hand into the mouth while eating transmits the virus to the throat resulting in the infection. Touching the eyes with the infected hands may also result in Influenza.

After entering the body, the Influenza virus attaches itself to the cells of the throat and then enters the cells. It divides inside and destroys the cells. After that the virus exits and enters the adjacent cells destroying them as well. The process continues resulting in damage to a large part of the tissue. Various chemicals, such as cytokines, interleukins, will be released because of the infection, which cause fever, headache or weakness.

In severe cases, the virus may spread to the lungs and damage them leading to Pneumonia.

Symptoms of Influenza (Flu)

Symptoms of Influenza usually start abruptly one to two days after contacting the virus.

There may be chills or chilly sensations (shaking or shivering of the body), fever, sore throat, dry cough, headache, body aches (especially of joints) and weakness. In some people, the eyes may become red due to irritation, and they may water excessively. There may also be pain on moving the eyes.

Nausea, vomiting, pain in abdomen or loose stools (Diarrhea) may also occur, especially in children. In some people, the body aches and joint pain may be very severe.

In most cases, the symptoms resolve within a week or two after the infection.

In severe cases, infection may spread to the lungs resulting in shortness of breath, increased breathing rate, persistent high fever, and cough with yellow greenish discharge or pain in the chest region.

Tests and Diagnosis of Influenza (Flu)

Diagnosis of Influenza infection is mainly based on symptoms.

The usual diagnostic tests done in Influenza infection may be:

  • Blood tests may be done to detect total number of white blood cells (total leukocyte count) and their different types (differential leukocyte count).

  • Chest x ray may be done in severe cases to detect any abnormality in the lungs.

In some cases, blood tests may be done to detect antigens or the antibodies produced against the Influenza virus.

In some cases, samples are taken either from the throat by rubbing a clean cotton piece, or from the discharge in the sputum. They are used for virus culturing test.

Treatments for Influenza (Flu)

The primary aim of the treatment is to relieve the symptoms till the infection subsides.

General Measures

Bed rest may be advised for a few days. One should take a lot of fluids and avoid alcohol and smoking. An infected person should isolate himself or herself from others for few days till the symptoms subside.


  • Paracetamol may be advised to relieve fever, headache and body aches associated with flu. Cough syrups may be given to ease cough, if it excessive.

  • In case a person has Pneumonia, any previous heart or lung disease, or has weak immune system such as in cases of HIV infection, antiviral drugs such as Tamiflu, amantadine and rimantadine may be given. They act by decreasing the action of the virus and reducing their spreading in the body. These medications are more effective when taken within forty-eight hours after the infection.

  • Sometimes, antiviral drugs such as chemoprophylaxis may be given to the family members of an infected person to prevent them from catching the infection. 

  • Antibiotics may be given when there is a bacterial infection such as in cases of Pneumonia.

  • If symptoms suggestive of pneumonia appear, immediate hospitalization should be done and adequate oxygen is given.

Side-effects and Complications

  • Influenza may recur. This is because the virus goes through frequent genetic mutations every year. A person may not have immunity to a new strain of virus. This makes Influenza a serious contagious disease.

  • Aspirin or other salicylate drugs taken by children who have Influenza may result in Reye’s Syndrome. There may be severe damage to organs such as the brain and the liver, and may even lead to death.

  • In some cases, Influenza infection may result in Pneumonia (infection of the lungs). Pneumonia is caused by Influenza virus or by bacteria. In some other cases, there may be infection of the sinuses (a condition known as Sinusitis) or of the ear. Such complications are more common in very old and very young, in pregnant women, and in people with any previous long term diseases or in people who have a weak immune system as cases of HIV infection.

  • In people who have any existing heart condition such as Coronary Heart Disease, or any lung disease such as Chronic Bronchitis or Asthma, or a kidney disease such as Chronic Kidney Failure, Influenza may worsen the existing disease which may even lead to death.

  • In some cases, Guillain-Barre syndrome may develop because of an autoimmune response to the Influenza virus or to the Influenza vaccination.

Self-care and Important Considerations

  • One should wash hands regularly with soap and water or with alcohol-based hand rubs after coming from outside.
  • One should regularly clean doorknobs, light switches, blankets, food utensils and other household items especially if a family member is infected. At home, this can be done effectively with diluted chlorine bleach. Clothing and bed sheets of the infected person should be handled with care and washed regularly. Face mask should be used by the person who is providing care to the infected person. One should know what kind of masks to be used and how to wear them.

  • One should be able to recognize the symptoms such as fever with cough, sore throat and/or nasal congestion and contact a doctor if such symptoms appear. Flu can be identified by a sudden onset of high fever and extreme weakness that usually does not occur in common cold.

  • An infected person should wash hands regularly, avoid spitting, and cover nose and mouth when sneezing or coughing. One should avoid close contact with others, especially with young children, pregnant women or old people.

  • Aspirin or other salicylate drugs should not be given to children who have flu.

  • Vaccinations against Influenza may be given during epidemics to prevent the virus from spreading. They may also be given to children or very old people or to those who have any heart or lung disease or to persons with a weak immune system. The vaccine takes about two weeks to turn effective. Vaccination is safe but has to be repeated every year. It is possible to get vaccinated and still catch flu because the vaccine is not effective against all strains of Influenza virus. One should contact the doctor if a vaccination causes any allergic reaction such as redness over the skin or breathing difficulty.

  • People should be extra vigilant during epidemics of flu and should follow all hygienic measures stringently.

This article is developed by our team of Doctors/Experts. Last updated in 20th December,2010. Please see our Editorial board for details.
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