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Influenza    See images

Overview | Symptoms | Treatment | Prevention

Alternative names:

Flu; Influenza A; Influenza B; rarely Influenza C

Definition:

A contagious viral infection of the nose, throat and lungs which often occurs in the winter.

Causes and Risks

Influenza is a common viral infection.  It is caused by three viruses - Influenza A, B and C. Type A is usually responsible for the large outbreaks and is a constantly changing virus. New strains of Type A virus develop regularly and cause new epidemics every few years. Type B causes smaller outbreaks, and Type C usually causes mild illness.   In the United States,  infection with influenza A and B leads to 20,000 deaths and over 100,000 hospitalizations each year.  Influenza is transmitted person to person via contagious droplets that are formed when someone sneezes or coughs.

Certain individuals are at higher risk from complications of influenza and therefore vaccination is recommended for these high risk groups. This includes people aged 50 or older, people with diabetes, or with medical conditions affecting the heart,  lungs (i.e asthma) or kidneys; health care workers and anyone with a weakened immune system (HIV, etc.). Supplies of vaccine are limited each year, but after high-risk people have been vaccinated, anyone desiring protection can request vaccination. 

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