Contagious Period and Duration of Seasonal, Swine and Bird Flu

Incubation Period vs Contagious Period

Incubation (Lat. incubationem = a lying upon eggs) period is the time from exposure to a microbe (like influenza virus) to the appearance of the first symptoms. It is important to note that even though a person may be exposed to a microbe, they may not be infected with it and therefore there will be illness.

Contagious (Lat. contingere = touch closely) period is the time during which an infected person is able to spread an infection to others. This may be through physical contact (touch), sexual transmission, droplet spread (cough/sneeze) or even sharing of personal items.

A person who has a contagious illness should be isolated (not necessarily quarantined) in order to prevent further spread. Other people who are at risk of contracting the infection, like young children, the elderly, pregnant women or those with chronic conditions, should limit contact with the person who is ill. Care and assistance from family members is necessary for recovery and this should be undertaken by those who are not at risk and healthy.

Table 1: Incubation and contagious period of seasonal, swine and bird flu

SEASONAL INFLUENZA About 2 days (1) From 1 day before symptoms appearance to 7 days (or more in children), or 24 hours after cessation of fever (2)
SWINE FLU – 2009 PANDEMIC INFLUENZA H1N1 1 – 7 days (3) From 1 day before symptoms appearance to 7 days (or as long as symptoms last) (3)
BIRD FLU – AVIAN INFLUENZA H5N1 2 – 17 days (4)* 7 days (up to 21 days in children) after symptoms appearance (5)*

*In bird flu, incubation and contagious period are not yet exactly determined.

All types of influenza, when there are no complications, usually last up to seven days. If you have symptoms of influenza, you should stay at home, avoid physical effort (preferably stay in bed) for at least 24 hours after cessation of fever.

Proper hygiene is also important in stemming the spread of infection.

  • Throw away used tissue paper.
  • Wash your hands regularly.
  • Block your mouth and nose when sneezing or coughing.
  • Do not share foods or drinks with any other person.

How Long Do Seasonal, Swine and Bird Flu Last For?


Main symptoms of all types of influenza (seasonal flu, swine flu – 2009 pandemic influenza H1N1, and bird flu – avian influenza H5N1), like fever, severe tiredness, runny nose and sore throat, usually last for 5-10 days.

  • The first symptom, fever, usually lasts for 1-2 days, sometimes up to 5 days (1). Note: Fever may be absent.
  • Severe tiredness may be present in the first 3-4 days.
  • When fever starts to drop, sore throat, dry cough, runny nose and headache appear or worsen and may last until 5th to 10th day of the disease.

If above symptoms do not cease in 7-10 days, you should visit your doctor to get an exact diagnosis and to check if eventual complications, like sinusitis or pneumonia have developed.

Other relatively mild symptoms, like dry cough and fatigue, may last for up to 2 weeks or more.

You can go back to school or work 24 hours after you no longer have fever after your last dose of a fewer-lowering drug (2).

Duration of flu depends on:

  • Strength (virulence) of viruses that attack you. Viruses in one epidemic can be strong, in an other one week. Even viruses within one epidemic can vary in strength.
  • Age. In general, in children symptoms of flu tend to be worse and last longer than in adults.
  • Your overall health. In people with low immunity, malnutrition, in chronic patients or alcoholics, symptoms tend to last longer, and complications are more likely.
  • Treatment. Anti-flu medications can shorten the duration of flu for a day or so and may prevent complications (2), like pneumonia. Fever-lowering drugs, like Tylenol or Advil, usually shorten the duration of fever.

Other infections with flu-like symptoms lasting for about a week:

  • Common cold
  • Croup
  • Viral pharyngitis
  • Viral laryngitis
  • Strep throat
  • Stomach flu – gastrointestinal infection caused by Rotavirus
  • Measles, chicken pox and other childhood infections with rash
  • Bacterial pneumonia (if treated)

Symptoms lasting for more than two weeks speak either for complications of flu (sinusitis, pneumonia, myositis, pericarditis, myocarditis, meningitis, encephalitis, and so on) or for infections, caused by other microbes, like:

  • Infectious mononucleosis, caused by Epstein-Barr virus (EBV)
  • Acute viral or bacterial sinusitis
  • Whooping cough
  • Viral pneumonia
  • Atypical pneumonia
  • Tuberculosis
  • Lyme disease, caused by bacterium Borrelia burgdorferi
  • Q fever
  • Psittacosis


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