Influenza, commonly known as the flu, is a viral infection caused by the influenza virus. It is also commonly referred to as the seasonal flu because it is more likely to occur during certain periods in the year. The infection usually spreads through aerosol drops expelled by coughing and sneezing. The virus is inactivated by sunlight, disinfectants hence frequent hand washing reduces the chance of infection.

Commonly occurring symptoms are chill, fever, sore throat and generalized weakness. The most common and serious complication of influenza is viral and bacterial pneumonia. These complications can be fatal in extremes of ages, both in the elderly and young children, in pregnancy and in people with poor immunity. Bed rest and plenty of fluid are usually sufficient to manage influenza in most instances. Antivirals like oseltamivir are prescribed in cases likely to develop complications. Vaccines are available against attacks of specific strains of influenza virus but are not always 100% effective as the virus mutates rapidly.


Symptoms of influenza are similar to that of the common cold, another acute viral infection. The difference in symptoms is that symptoms of the common cold develops gradually whereas symptoms of influenza develop rapidly. Symptoms of influenza include :

  • High fever usually above 100°F associated with chill and sweating
  • Muscle pain
  • Headache
  • Dry cough
  • Nasal congestion, runny nose and sneezing
  • Flushing of the face
  • Poor appetite
  • Red watery eyes
  • Skin rash
  • Diarrhea, abdominal pain and nausea may occur in children.
  • Attack of influenza worsens symptoms of asthma and other breathing problems.

Complications of influenza infection includes :

  • Secondary bacterial pneumonia
  • Bronchitis
  • Sinus infection
  • Ear infection


A person remains infective to others usually from the day before appearance of the symptoms to 5 to 7 days after symptoms resolve although the duration may vary. Infectivity (shedding of the virus) of a person varies with the degree of temperature. Children are more infectious and shed more virus in comparison to adults.

There three main ways of transmission of influenza virus, namely :

  • Airborne (via aerosol drops).
  • Direct transmission of secretions.
  • Contact with contaminated surfaces like bank notes, door knobs, computer key boards, phones, household objects and personal contact like hand shake.

Influenza virus produces seasonal epidemics around the world killing millions of people. Newer strain of influenza virus appears when the existing virus picks up new genes from virus infecting species other than humans, such as birds and pigs. Viruses previously infecting only animals of other species may then start infecting humans. One of the recent outbreaks of influenza is by H1N1 virus (swine flu). H1N1 virus has picked up genetic material from three species humans, pigs and birds.

Risk factors

Chance of infection increases in :

  • Elderly patients over 65 years, although attack of swine flu was more common in teenagers and children.
  • Day care center workers and health personnel.
  • Residents of hostels, military establishment where large number of people reside at a time.
  • Poor functioning of immune system: HIV/AIDS patients, cancer, organ transplant, long term steroid intake, anti cancer drug treatment.
  • Co-existent chronic illness like asthma and diabetes.
  • Pregnancy.


In absence of complications and in healthy young adult subjects plenty of fluid and bed rest is adequate. Patients with increased risk of development of complications are treated with :

  • Antivirals such as oseltamivir.
  • Antibacterial in the event of secondary bacterial infections.

Vaccines against specific strains of influenza are available, although as the virus changes rapidly its genetic make-up vaccine effective one year may not be so next year.

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