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Every winter we can expect influenza outbreaks. About 100 million people will be infected this season in the Northern Hemisphere. That translates into one in three children and one in 10 adults.

Most people are surprised to hear that influenza is the fifth leading cause of death in Canada after cardiovascular disease, cancer, chronic obstructive pulmonary disorder and unintentional traumatic injury.

Deaths range from 500 to 1,500 annually from influenza and pneumonia, but as many as 4,000 to 8,000 from complications relating to influenza.

Individuals with underlying chronic disease or those who are elderly are more at risk of dying from flu complications. Even so, about 20 per cent of such deaths still occur in patients who were otherwise well and healthy prior to infection.

The common use of the word flu to describe any cold or virus that we get has led to confusion about what is influenza. Patients will often come into my office and say they have the flu, when what they mean is that they have a constellation of symptoms that are flu like, but not necessarily caused by an influenza virus.

Influenza is very contagious. When an infected person coughs or sneezes, the virus spreads in water droplets and small particles in an aerosol spray. That virus then enters another's body through the nose, mouth and eyes.

We see influenza in all age groups. Children, however, have higher rates of infection than adults and usually are the cause of spreading influenza within a family. When we have an influenza outbreak, as many as 40 per cent of preschool children can be involved. About 12 per cent of children under the age of 2 get the flu and as many as 43 per cent of people between 15 and 64.

Aside from feeling awful, influenza is responsible for absenteeism from school and work, disruption of family and social life, increased visits to doctors and as many as 70,000 to 75,000 hospitalizations in Canada. More than 60 per cent of complications can occur in otherwise healthy people. Those complications can include bronchitis, pneumonia, sinusitis and worsening of any pre-existing disease.

Often there is the inappropriate use of antibiotics for individuals with the flu, and that contributes to the risk of antibiotic resistance. It is estimated that 30 to 45 per cent of patients who go to a doctor with influenza or influenza like-illness will get an antibiotic prescription. For those with complications attributed to influenza, that number of antibiotic prescriptions can be anywhere from 60 to 80 per cent.

Primary prevention of the flu starts with flu vaccine that is offered every fall. The World Health Organization keeps track of new and emerging strains of the flu. The vaccine provides protection against the three strains thought most likely to cause a problem in the coming flu season.

Influenza can be differentiated from a cold by its symptoms. Unlike a cold, which is usually gradual in onset, influenza is sudden. Cough is often present and a severe headache accompanies the flu. Influenza usually has severe muscle aches and pains and the accompanying fatigue and weakness can last up to two or even three weeks.

So, what can you do to reduce the likelihood of getting the flu? Hopefully, you were vaccinated Make sure you wash your hands frequently and thoroughly. Cover your mouth and nose with a tissue when you cough or sneeze and if that is not possible then use the "sneeze sleeve" by coughing or sneezing into your upper sleeve.

If you think you have influenza, you have the option of treatment with an antiviral medication. Present antiviral medications include oseltamivir (Tamiflu), zanamivir ( Relenza) and amantadine. High levels of virus resistance to amantadine often limit its use, meaning that amantadine isn't very effective against many strains of the flu.

For either oseltamivir or zanamivir to be effective, they must be begun within a 48-hour window of starting symptoms of influenza.

Oseltamivir is a pill and is given for both prevention and treatment to adults and children over one year of age. Zanamivir is also used for both prevention and treatment in adults and children over seven years old. Treatment can reduce the duration and severity of illness by 30 to 40 per cent and can reduce the secondary complications by about 50 per cent.

Antiviral drugs for influenza will only work on the influenza virus. These medications are also used to control outbreaks in institutions such as nursing homes.

Many people are concerned about bird flu and wonder whether the present vaccine can protect them. There is no vaccine at present for the bird flu. That's because the virus that could pose a widespread threat to humans has not yet emerged. Some people in close contact with infected birds have become sick. But, for now at least, the "bird flu" isn't very effective at being transmitted from one person to another.

Remember to talk to your doctor about any concerns you might have. You can also visit the Health Canada web site, http://www.phac-aspc.gc.ca/influenza/fam_e.html.

Dr. Marla Shapiro can be seen Tuesdays on CTV's Canada AM.